PHYSICO-CHEMICAL BEHAVIOUR OF AQUEOUS AND NON - AQUEOUS SOLUTIONS OF AMPHIPHILIC

MOLECULES IN PRESENCE OF ADDITIVES

81IMAIARY

THESIS SUBMITTED FOR THE AWARD OF THE DEGREE OF

JBottor of $I)tlogopt)p IN

CHEMISTRY

SY

Mrs. KIRTI

DEPARTMENT OF CHEMISTRY ALIGARH MUSLIM UNIVERSITY

ALIGARH (INDIA)

1996

SUMMARY

There is a class of compounds called surfactants

that decreases strikingly the surface tension or

surface free energy of interfaces. This thesis is

concerned exclusively with certain properties of the

surfactants.

Surfactants generally consist of two distinct

parts, a hydrocarbon portion and a polar or ionic

portion in the same molecule. The hydrocarbon portion,

which can be linear or branched, interacts only very

weakly with water molecules in an aqueous environment.

Moreover, the strong interactions between the water

molecules arising from dispersion forces and hydrogen

bonding act cooperatively to squeeze the hydrocarbon

portion out of the water, hence the chain is usually

called hydrophobic. The polar or ionic portion of the

molecule, usually termed the head group, however,

interacts strongly with the water via dipole - dipole

or ion - dipole interactions and is solvated.

Consequently, the head group is said to be hydrophilic.

Depending on the chemical structure of the

hydrophilic moiety bound to the hydrophobic potion, the

surfactants may be classed as cationic, anionic,

nonionic, or ampholytic (zwitterionic). Both the

interfacial properties and bulk properties of solutions

of surface active agents are consistent with the fact

that at a certain concentration the surface active

molecules associate to form longer units. These

associated units are called micelles. The concentration

at which this association phenomenon occurs is known as

the critical micelle concentration (cmc). The value of

cmc is dependent upon a large number of parameters like

total carbon chain-length, additional polar groups, C=C

bonds, chain branching of surfactants, various types

of additives (polar and non-polar), electrolytes,

temperature, and pressure.

While stupendous work on surfactants is reported

in literature and today thousands of surfactants are

available, studies are still underway to examine

various factors responsible for their micellization and

micellar growth and adsorption behaviour under

different conditions. Several micellar systems have

recently attracted considerable interest because of

their potential uses in diverse fields. An interesting

aspect of micellar solutions is that they show a large

change in viscosity on adding inorganic salts or

organic cosurfactants. From a practical point of view,

alcohols (as cosurfactants) have been used in tertiary

oil recovery because they bring about a large decrease

of viscosity, strongly accelerate the rate at which

these systems reach equilibrium in the polyphasic

range, and appear to decrease the adsorption of the

surfactants in rock pores in the oil field, thereby

increasing efficiency and decreasing cost. The viscous

surfactant solutions are also of industrial importance

because they enhance customer appeal and economy of

various formulations. Usually, inorganic salts are used

as thickening agents for concentrated surfactant

solutions; the role of organic molecules as thickening

agent is, however, not well studied.

The simplest possible aggregate of surfactant

molecules is the micelle. At the molecular level, a

balance of interfacial forces controls the curvature of

the surfactant film which, in turn, determines the

shape of the aggregates. It is now accepted that

micelles are spherical near cmc. Transition of

spherical to larger micelles for ionic surfactants

occurs upon a reduction of inter head group repulsion.

It may be caused by salt or surfactant additions or

solute solubilization. It is not clear if, at

surfactant concentrations, micellar growth by

increasing salt concentration is because of enhanced

screening of the eletrostatic interactions or due to

change in "electrical charge per head group".

The solution viscosity responds to changes in both

the structure of aggregates and their mutual

interactions. In dilute solutions (where these

interactions are minimized) the technique is sensitive

to the shapes of particles in the solution. Transition

from small to large micelles is accompanied by a

significant increase in viscosity and appearance of

anisotropic susceptibilities.

Due to solubilization properties, the micellar

systems have several applications; thus a careful

investigation of such properties is of paramount

interest. The site of solubilization of different

compounds within the micellar systems can be correlated

with the structural organization of aggregates. A large

body of work is available on solubilization of organic

compounds by surfactant micelles but structural changes

produced by such additives have not been studied in

much detail. Solubilization results of polar organic

molecules are consistent with other physical evidences

indicating that these molecules have their head group

anchored in the polar/ionic outer region of typical

ionic surfactants. Such molecules tend to solubilizC

atleast partly within the hydrocarbon core of the

micelle, although steric and substituent group effects

may play important roles in modifying the structure and

thermodynamic properties of"intermicellar solutions" of

the organic solute in the micelles.

There has been considerable discussion in the

literature about the location of organic solutes in

ionic surfactant micelles. The aromatic hydrocarbons

are intermediate in behaviour between moderately polar

solutes (e.g. , hydroxy substituted benzoates, organic

acids, amines, medium chain alcohols, etc.) which are

clearly intercalated in the micelle surface region and

aliphatic hydrocarbons which preferentially solubilize

in the mi cellar core region. These facts explain why

the effect of organic additives on the properties of

micellar systems is a topic of importance.

In the thesis the first Chapter is "General

Introduction". It is entirely based on up -to- date

literature survey relating to the work described in

preceding chapters.

Viscometric studies of the effect of added n-

alcohols (C3 - CsOH) and n-amines (C4, Cg - C8NH2) on

the micellar growth of cetylpyridinium chloride (CPC)

in the presence and absence of potassium chloride (KCl)

at four temperatures between 25 - 40° C are described

in Chapter II. The presence of KCl or organic additive

of lower chain-length (C3OH, C4OH or C4NH2) singly or

jointly has little effect on the viscosity of the

micellar solutions. With higher chain - length (C5OH

CeOH, Cg - C8NH2) additives the viscosity increases as

the additive concentration increases; magnitude being

substantial in presence of KCl. Moreover, for equal

chain-length additives the effect was greater for n-

alcohols. An interesting observation was that in

presence of KCl and with the additives C5OH, CgOH or

C7NH2, the viscosity of CPC micellar solution increases

with increase in the additive concentration (similar to

the case without KCl), reaches a maximum, and then

decreases. In all probability, the other alcohols and

amines, viz. C7OH, CgOH and C8NH2, would show the same

phenomenon at higher additive concentrations, but

studies were - hampered as turbidity appeared at

concentrations before such maxima could occur.

These two effects show that a special phenomenon exists

when O.IM KCl and additives are present in the same

system. The manifold increase in viscosity is the

result of variation of different forces favorable for

micellar growth. Addition of KCl to the CPC solution

weakens the Coulombic repulsion between the micelles,

and intercalation of higher chain- length additives

decreases intramicellar Coulombic repulsive forces and

increases hydrophobic forces among the monomers of the

CPC micelle. As mentioned earlier, the decrease of

Coulombic repulsion and / or increase in hydrophobic

interactions are favorable conditions for micellar

growth (either one of which exists if O.IM KCl or

organic additive is present singly).

The observed viscosity decrease at higher

concentrations with the aforementioned additives is

possibly due to the fact that they may be salted - out

by the added 0.IM KCl and start dissolving in the

micellar core rather than remaining in the vicinity of

interfacial region; therefore the requirement of the

surfactant chains to reach the centre of the micelle

become relaxed. It is, thus, possible that at high

additive contents the larger micelles disintegrate to

smaller ones and form the basis of the viscosity

decrease. The solubility and packing constraints do

not allow C7OH, CgOH or CBNH2 to do so as there is not

a sufficient amount of these additives available to

form the core of the micelle (solubilized system).

Thus, it was concluded that the presence of a salt

and an organic additive in the system produce favorable

conditions for micellar growth. The electrostatic

effect produced by additives at the micellar surface is

the governing factor in addition to the hydrophobic

part of the additives. In case of additives of equal

chain-length, its efficacy of decreasing effective

head group area at micellar surface (AQ; decides the

potential of the additive for structural growth.

Temperature dependence of the viscosity was used to

compute the free energy of activation,^G*, for the

viscous flow.

In Chapter III, the effects of the addition of

aliphatic n-amines ( C4, Cg, C7 and C8NH2) and

temperature on the shape of cetyltrimethylammonium

bromide (CTAB) in 0.IM KBr, studied by viscosity

measurements, are described. The data show that

transition of rod-shaped micelles to larger aggregates

is induced by addition of higher amines (Cg - C8NH2)

upto a certain concentration, a further increase in

concentration produced the opposite effect. With C4NH2,

the viscosity decreased gradually right from the

beginning. Activation free energies ( A G * , computed

from the temperature dependence of the viscosity) were

higher for larger aggregates than for smaller ones. The

data were interpreted in terms of solubilization /

incorporation (decrease of micellar surface charge

density) of amines at various sites of micelles.

The shear viscosities of CTAB micellar solutions

in presence of aromatic compounds (sodium salicylate,

NaSal, sodium benzoate, NaBen, salicylic acid, SA, and

anthranilic acid, AA) at different temperatures were

measured which are given in Chapter IV. A Brookfield

viscometer (model DV - 1+) with cone / plate geometry

was used to obtain the viscosities at different shear

rates. The data were collected for fixed CTAB

concentrations (0.05, 0.10 and 0.20 M) with varying

concentrations of the additives. For all the systems,

the viscosities were highly dependent on the rate of

shear ( non-Newtonian flow) and exhibit viscoelastic

character. The zero shear viscosity (HGSO) VS• [NaSal]

plots showed a two - peak structure. Similar behaviour

was obtained with NaBen. It was also seen that the I^G=0

slightly decreased with temperature but positions of

the maxima and minimum remained unaltered. With SA and

AAjonly a single peak (though broad) was observed which

broadened and shifted to higher [additive] as the

[CTAB] was increased.

With the addition of NaSal in 0.IM CTAB, while

intermicellar correlation diminishes (owing to the

electric shielding), the micellar size or rod length

increases and these long micelles entangle with each

other. This is the reason for initial steep rise in

^G=o values as we increase the amount of NaSal.

Penetration of Sal" into micelles increases the Rp

(Sal" binds strongly to CTA+ cation which could reduce

A Q ) - Also, the phenyl moeity of the salicylate might be

embedded into the micellar hydrophobic region. The

result then is the trend short rod-shaped micelles i*

large wormlike micelles and hence a steep rise in the

viscosity was observed. Beyond first maximum, further

addition of NaSal .destroys intermicellar correlation

(entanglement to disentanglement) owing to the electric

shielding effect. As a result, the rheological

character diminishes in opposition to micellar growth,

and the nQ=,o ^^ decreased. With the addition of excess

NaSal {>[CTAB]}, the specific adsorption and

penetration are promoted which accelerate the growth of

rodlike micelles and the viscosity rises upto the

second maximum due to entanglement. As the

concentration is . increased further, the excess

adsorption and penetration of Sal" allow the micelles

to charge negatively and to diminish destructively to

smaller sizes because of the electrostatic repulsion

(the micelles are now negatively charged). Similar

behaviour was observed with NaBen.

Interestingly, only a single peak was observed

with both the AA and SA and thus the behaviour of these

acids was different than the NaSal or NaBen. This may

be due to the fact that with these acids electrostatic

interactions are not that strong as the case with

NaSal or NaBen.

These acids interact, in the first approximation,

due to a combined effect of eletrostatic and

hydrophobic forces with the micelle and, after

saturating the palisade layer, they can get adsorbed

at the surface of the micelle. This is responsible for

the fall of viscosity. It was further observed that, at

equal concentrations of SA and AA, the viscosities

were higher with the former. It may be due to the

fact that -NH2 group (of AA) is less effective in

transferring electron cloud to the charged acidic

group. It is,therefore, concluded that the chemical

structure of the additive has an important role to

play for such micellar growth processes.

* • • *

PHYSICO-CHEMICAL BEHAVIOUR OF AQUEOUS AND NON - AQUEOUS SOLUTIONS OF AMPHIPHILIC

MOLECULES IN PRESENCE OF ADDITIVES

THESIS SUBMITTED FOR THE AWARD OF THE DEGREE OF

Bottor of $IiiIo£iopIip IN

CHEMISTRY it

sv Mrs. KIRTI

DEPARTMENT OF CHEMISTRY ALIGARH MUSLIM UNIVERSITY

ALIGARH (INDIA)

1996

. . •^f; ' ;N^.*^^"L/E^^;.

" -^t

5 SEP 1997-

T4801

^0eclccafed to-

and

PROF. KABIR -UD-DIN Pnnhjps J ^^^ ' '^^'^^^ ^ DEPARTMENT OF CHEMISTRY I inter. 317, 318 ALIGARH MUSLIM UNIVERSITY A L I G A R H —202 002

Dnled . \ ,f-o3-,Wt

This is to certify that the thesis entitled

"PHYSICO - CHEMICAL BEHAVIOUR OF AQUEOUS AND

NON-AQUEOUS SOLUTIONS OF AMPHIPHILIC MOLECULES IN

PRESENCE OF ADDITIVES" is the original work carried

out by Mrs. KIRTI under my supervision and is

suitable for submission for the award of Ph.D.

degree in Chemistry.

(KABIR-UD-DIN)

ACKNOWLEDGMENTS

Special thanks are due to my supervisor. Prof.

Kabir-ud-Din, who offered encouragement, and

constructive criticism with a lot of patience

throughout the tenure of ray work in this laboratory. I

must express my deep sense of gratitude to my senior

Dr. Sanjeev Kiaaiar, Research Associate, for his helpful

comments, invaluable guidance, cooperation and

encouragement at every stage of this work,

I am grateful to Prof. Nuzrul Islam, Chairmcui,

Department of Chemistry, for providing the necessary

research facilities.

I also acknowledge the help offered to me by m/

friends. Dr. M.Z.A. Safiquee, Miss Sara Liz David, Miss

Deepa Bansal, Miss Uzma Naseer, Mr. S.M. Nair, Mr.

Rayees Ahmad Shah, Mr. V.P.M. Ashnif and Mr. Md. Akram,

and many others.

I am extremely beholden to my parents, in-laws and

all other family members for their affectionate

encouragement euid interest in my academic pursuits.

Words are insufficient to express my sincere

gratitude to my husband Mr. Dinesh Kumar, for his

loving care, devotion and support at all the crucial

hours of my need.

;-(>

(Eirti)

CONTENTS

Page List of rublicatioa• I

List of P^Ders Presented/Accepted

in Coii.''i iuc&a II

ClLapter - I

General Introduction .1

References 50

Chapter- II

Effect of Aliphatic Alcohols/Amines and Teoiperature on the Micellar Growth of Cetylpyridiniura Chloride Micelles in the Presence and Absence of Potassium Chloride 66 Experimental 70

Results 72

Discussion 72

References 112

f^ ipter - III

Effect of Aliphatic amines and Temperature on the Structural transition of Cetyltrimethylammonium Bromide Micelles in Aqueous Potassium Bromide Solution 116

Experiment 119

Results 119

Discussion 133

References 139

Chapter - IV

Non-Newtonian Viscosity Measurements on Cetyltrimethylammonium Bromide-Miceliar Solution in Presence of Few A.romatic Salts and Acids 141

Experiment 147

Results 3 43

Discussion 1 3

References 172

LIST QF POBLICATIOWS:

1. Effect of Solubilized Amines on the Structural

Transition of Cetyltrimethylanmonium Bromide

Micelles in Aqueous Potassiiim Bromide.

J. American Oil C3iem. Soc, 71, 763-766 (1994).

2. The Role of Alkemols in Micellar Growth: A

Viscometric Study.

J. American Oil Oiem. Soc, 72, 817-821 (1995).

3. Micellar Growth in Presence of Alcohols and Amines:

A Viscometric Study.

Langnuir, 12 (1996) (in press).

i i

LIST QF PAPERS PRESKHTKP/ACCBPTKD JM COKFEBSaCRSs

1. Effect of Surfactant Concentration on Viscosity

Behaviour of Cetyltrimethylammoniuia Bromide (CTAB)

Micelles in Aqueous Sodium Salicylate (NaSal),

Proc. Solid State Pfays. Syap., Jaipur, India, Dec.

27-31, 1994, p.401.

2. Viscometric Studies on tbe Micellar Growth with

Aliphatic Alcohols/Amines, International Sy^p. on

Micelles, Microemulsions and Monolayers: Quarter

Century Progress & Hew Horizons, Gainesville,

Florida, U.S.A., August 20-30, 1995.

CHAPTER - I

GENERAL INTRODUCTION

In biochemistry and molecular biology, one is

interested in colloids in aqueous solutions since most

of the reactions take place in an aqueous environment.

This thesis is concerned exclusively v^t' the

association colloids which consist of ampnxphilic

molecules (e.g., surfactants). There is considerable

interest in the nature of the structural organization

of multimolecular assemblies of surfactant molecules.

Recently, much efforts are being directed towards the

utilization of organized media to modify reactivity and

regioselectivity of products. Among the rany ordered or

constrained systems utilize*^ to organize the reactants,

the notable ones are micelles, microemulsions, liquid

crystals, etc. A fundamental understanding of the

physics of surfactant organized assemblies (SOA's),

t jir unusual properties and |>-..se behaviour ai j

essential for industrial technologists.

The modification of surface chiracteristics of

fluids in the presence of substances introduced from

outside is of tremendous utility. Such type of foreign

substances (derived mostly from fatty acids, fatty

alcohols, alkyl phenols, alkyl amines, mercapt-TS and

from variety of other sources) are known as surface

active agents or surfactants or detergents. Amphiphilic

molecules generally consist of two parts, namely, a

hydrophilic (water soluble) or polar part, and a

lipophilic (oil soluble) or non-polar part^"*. The

lipophilic part is generally a .''.ong hydrocarbon chain.

Owing to the polarity of the distinct regions these

substances have also been referred to as amphipathic,

heteropolar or polar-nonpolar substanco^'^. Depending

on the chemical structure of the liydrophilic moiety

bound to the hydrophobic portion, t)'3 suvfactaiat may be

classed as cationic, anionic, nonionic, or ampholytic

(zwitterionic)''"^^. An exhaustive list ol both

synthetic and naturally occurring surfactants is

available. Their preparation '' —perties in general

have been given in the e.^cellant ^ jraph of Fendler

and Fendlerl2 , The characterisi,ij properties of

surfactants in solution which render possible their

practical applications such as wasiiing, ileanirj,

wetting, emulsifying, dispersing ' 7 depend in

all cases on the tendency of th>js3 comT>ounds to

accumulate at interfaces between « solution and the

adjacent gaseous, liquid, or ' I phases^^, TVt

sufficient concentrations of aru ix- ilic molecules in

solution (of water or organic sol«w;nt8) aggregates

called micelles may be formed. Micelles do not exist at

r

all concentrations and temperatures. There is a very

small concentration range below which aggregation to

micelle is absent and above which association leads to

micelle formation. This concentration is called

critical micelle concentration (cmc). The critical

micelle concentration depends on the length of the

hydrocarbon chain. Generally, the cmc decreases as the

hydrocarbon chain-length increases. The position of

head group in hydrocarbon chain also affects the cmc.

The closer the head group to the center of the chain,

the higher the cmc du? to two branches of the chain

partially shielding one another. The presence of double

bond in the chain also causes an increase in cmc.

For ionic surfactants the cmc first decreases with

increasing temperature at low temperatures and

increases at high temperatures^*. For nonionic

detergents the cmc decreases with increasing

temperature^^'^^.

The cmc increases upto a pressure of 1,000

atmospheres and decreases with further increase of

pressure^'7»18 _

The addition of salts decreases the cmc of ionic

detergents, while the micelle size increases. For non-

ionic detergents the addition of salts slightly

decreases the cmc and further increases it at higher

salt concentrations. Non-electrolytes like urea and its

derivatives (which are generally believed to be water

structure breakers) increase the cmc of ionic and

nonionic surfactants. Addition of aceta'^ide and

formamide decreases the cmc of surfactants.

The ni liber of molecules that aggregate to '"orm

micelles is called the aggregation number. :!icellar

aggregation can be demonstrated by meas uents of

physical properties against surfactant concentration.

The most significant property is surf.ice (or

interfacr'.al) tension (Fig. 1.1).

The most important property or micelles is to

solubilize the other molecules (water or organic

molecules) . When micelles solubilize other molccul'iS i

their interior, the resultant solution, composed of

three components- amphiphiles, wrter, and oil-. Is

called a microemulsion. This is the simplest possible

form of microemulsion, but in general, when

amphiphiles, water, and organic molecules form a

thermodynamically stable, optically transparert

solution, one calls it a microemulsion, even though it

may have a rather complicated structure. The ability to

dissolve another molecule is called the ^solubilizing

6

c o o l _

c u

§ o

<- o c -^ o o o a>

5 tn

o .2

c S o 3 O *- ~ 0)

« E o

(A C 3

.2 S c ^ 0) 8 •

1 ° i o * •^ 1 o o

0, 1 5 c

3 5 en o

o> £ *— P

O

x> c o

1

c o x: (/)

.52

c o 3 O

H-

o

3 O 3 t in

_ O

6 u « i « *

c o

c 0) u c o u

D

E .^ o

u

uoisuai 93opns

power' of the micellar Bolution.

The reason *why do micelles form' may be explained

by taking into account the changes occurring when a

monomer is transferred from its aqueous environment

into the micelle. On transferring the monomer into

micelle, the high energy of the hydrocarbon/water

interface is lost, as the chain is now in contact with

others of a like nature. Transfer of monomer into

micelle also means that the structuring of water around

the hydrocarbon part of the monomer is lost, therefore

an ordered state has become a disordered one with

regard to the water, implying a positive entropy change

and a decrease in free energy. The factor opposing the

micelle formation in ionic surfactants is rise in free

energy due to incorporation of monomer into a micelle.

This disorder to order transitioa gives a negative

entropy change which will oppose the positive entropy

changes occurring from loss of water structure. The

overall decrease in free energy due to loss of

hydrocarbon/water interfacial energy and water

structure outweighs the free energy rise due to

electrical work and translational freedom losses,

giving a remarkable tendency to micellise. Mukerjee and

Mysels^9 have compiled cmc data of various class of

su r f ac t an t s .

The exact s t r uc tu r e of an aqueous micel le i s not

known wi th c e r t a i n t y , a l though s e v e r a l i n t e l l i g e n t

guesses have been put for th . Fig. 1.2 dep ic t s some of

these models.

Wojcaial Micelles

Aggregates formed in aqueous solutions of surfact­

ant molecules a t cmc are known as normal micelles. They

are always in dynamic equilibrium. Such micelles are

thought to be roughly sphericall2,20,21 A schematic

two dimensional representation of an ionic spherical

micelle i s shown in Fig. 1.3. The hydrophobic part of

the aggregate forms the core of the micelle while the

p o l a r head groups a r e l oca t ed a t t h e m i c e l l e - w a t e r

in te r face in contact with and hydrated by a number of

water molecules. The i n t e r i o r of a mice l le i s viewed as

being much l i k e a l i qu id hydrocarbon d r o p l e t .

The mice l l a r surface appears to be an amphipathic

s t ruc tu re which i s supported by the binding of both

hydrophobic organic molecules and hydrophi l ic ions with

mice l les . The amphipathicity i s a proper ty shared with

the surfaces of p ro te ins and membranes22,23

The surface of micelles formed from ion ic sur fac t ­

ants i s highly charged. About 80% of these charges are

1]

^ Ol

QC u

•}':m llL^'i 2.

^UM.I. «M t I '

I I 11

O ^

EC

O u?

I ^

o ^ E (o

o 3.

o I

JC u o X)

^ J

c o u 0

3

« T»

E

^^ c~ 00 Ok

w •o o E

o

u 3

in

u ?!

^ o a. E

3 O

o >

Ol iZ

: u

Ht—Sfern layer

Gouy Chapman double layer

F I Q - 1*3 •' A fwo-dimensionol schematic representation of the regions of a

spherical ionic micelle. The counferions (X) , the head group5((^i

and the hydrocarbon chains ('"x^'^jare indicated.

11

neutralized directly through the incorporation of

counterions into the micellar surface, forming the

Stern layer. The remainder of the counterions form the

diffuse Gouy-Chapman layer. The existence ot a substan­

tial net charge c t?:e micella:' surface provides a

large dip in electrical potential across the Stern

Icyer and attracts ions of opposite charge. The amount

of water f .1 the miceller interior varies from

surfactant to surfactant. Water is considered, at

present, to penetrate the micellar in: tace only upto

distances of approximc^teiy three to sir. carbon atoms.

It has been proposed that micelles are loose and porous

structures in which water and hydrophobic regions are

constantly in contact with each other.24,25

Results of light scattering, viscosity, diffusion

and ultra centrifugation studies on nonionic ceto-

macrogol micelles indicated their shape to be ellipsoi­

dal with an axial ratio of 2:1^6.

:gG verse Micelles

Surfactants in non-polar solvents in presence of

traces of water associate to form the Ec-called

reverse/inverted micelles. The structure of micelle is

reveiTfflHii, i.e„, the polar head groups of the monomer

12

being present in the centre and the hydrocarbon chains

extending outwards into the solvent. Such vicelles

could be formed in presence of traces of water which

forms a water pool in the interior of the micellar

aggregate. The size and properties of reverse micelles

vary with the amount of 'ater present^'^-SO A possible

structure of reverse micelle in a non-polar medium in

equilibrium with monomers is shown in Fig.1.4.

The inner cavity of reverse micelles has been

compared with the ac^ivt sites of f nzyK:es29,30 ?:atf;jc

in reverse micelles is expected to behave vjry

differently from ordinary water bt cause of extensive

binding and orientation effects induced by the polar

heads forming the water core-^^. Lately, enzymes have

been encapsulated inside the water ^ ol of the reverse

'.tticelles without affecting their activity^2_ Reverse

micelles are able to solubilize hydrophilic molecules

like enzymes and plasmids that are much larger than the

original water pool diameter. Such micelles can be

viewed as novel microreactors whose physical properties

can be controlled through the water content.

The discontinuity in some physical proper^v

(viscosity, solubility, surface tension, etc.) of the

solution can be used to identify the cmc, and

13

14

techniques such as scattering, ultracentrifugation and

viscosity are used to determine the size and shape of

the micelle. Some other techniques which have been

developed to determine the cmc include dye

solubilization^^,34^ water solubilization^S, nmr36,37^

etc. Different experimental methods available for

determining the cmc are listed in the compilations of

Shinoifti et al.^O, Elworthy et al.^ and Mukerjee and

Myselsl9_

The formation of micelles from more than one

chemical species gives rise to what are known as mixed

micelles. In the simplest case, binary or ternary

mixtures of surfactants of similar, but not identical,

chain lengths may be studied and the thermodynamics of

this type of micelle formation has been described^S,39

Clint^O developed an analytical description which

contained both micelle composition and monomer

concentration above the mixed cmc for mixtures of

nonionic surfactants. Clint's treatment assumed ideal

mixing in the micelle. Furthermore, the expressions of

Lange and Beck^l and Clint^O for the cmc values of

mixtures of nonionic surfactants has been

15

experimentally verified for cases where ideal mixing

might be expected. The properties of the mixtures of

anionic and nonionic surfactants^^, 43 and cationic and

nonionic surfactants^^ have been interpreted with the

aid of mixed micelle formation. It was pointed out that

the cmc of the mixed surfactants is lower than either

of the single surfactants'^^'^^ .

Another class of mixed micelles results when low

molecular weight molecules are solubilized by mi .relies

formed from surfactants containing a relatively larger

non-polar chain. The solubilized substances, also

called a penetrating additive^S^ may be located in the

hydrocarbon core^^ or the hydrophilic mantle*''"^^.

TheniiodviLaiiiics and Theories of Micellization

The self-association of the monomeric surfactant

molecules leading to the formation of micelles results

in a decrease in the overall free energy of the system.

The free energy changes which occur with increasing

detergent concentration are also manifestation of the

change in water structure50-53 and , hence, changes in

the entropy of the system. An^jhiphilic monomers with

long hydrocarbon chains increase the orderliness of the

structure of water by the formation of * icebergs'

around the hydrocarbon chains resulting in an entropy

16

decrease in the system. Aggregation of the amphiphiles

forming essentially spherical micelles in which the

hydrophobic hydrocarbon chains are located in the

interior and self associate, can reasonably be

considered to result in a break up of the icebergs

formed around the monomers and consequently in a large

entropy increase.

Thermodynamic parameters of micelle formation have

been calculated in a number of ways54-63 Equation

(1)5'' has been used for calculation of the standard

free energy change, A C^if

AG°m = RT Incmc - (RT/n ; InX^ (1)

where Xm is the mole fraction of micelles, m is the

number of monomers in the micelle, and the other

symbols have their usual meaning. The temperature and

pressure derivatives of Eq. (1) give the standard

enthalpy change, A ^°m' ^^^ volume change, AV°^, per

monomer, where,

^H°m = RT2 [d/dT Incmc]p + RT2/m [d/dT InX^lp ...(2)

and

AV°ni = RT [d/dP IncmcJT - RT/m [d/dP InXm] T (3)

When the cmc is expressed in mole fraction units,

the free energy changes obtained using Eq. (2) are in

unitary units. Since the aggregation number is often

17

not known, many workers approximate Eq. (1) by omitting

the second term and estimate ACni by the relation

AG'm = RT Incmc (4)

The second terms of Eqs. (2) and (3) are also dropped

from the right hand side . A relatively small error in

the calculated thermodynamic quantities is introduced

by this approximation57. The SkH ni of micelle formation

can also be determined by calorimetry, and it is of

interest to compare enthalpy changes determined by the

two approaches. Finally, the unitary entropy of micelle

formation, AS°ni' ^^ most often obtained from the

equation

AG°m =AH«'nv - TAS°ni (5)

and the change in heat capacity, ACp°inf can also be

determined from calorimetry and temperature dependence

ofAH°ni-

Tanford^S'^^ has given a theoretical basis to free

energy of micelle formation as the sum of hydrophobic

contribution and a size limiting term resulting from

repulsion between head groups

bG-ja = ^U-ni + Wm (6)

whereAU^m represents the contr ibut ion of the hydrocar­

bon t a i l (predominantly a s c r i b a b l e t o hydrophobic

r e p u l s i o n by the s o l v e n t ) and Wm r e p r e s e n t s the

18

contribution of the head group (predominantly repulsion

between head groups since the head groups remain in a

solvent environment when the micelle is formed). The

standard free energy change, £:iG°, can be described as

AG° =AG°0 + AG°e +AG°w (7)

where G''0 is the free energy change associated with

the transfer of the hydrophobic part of the surfactant

molecule from the aqueous medium to the micelle

interior of aggregation number m, G°Q is the free

energy associated with the electrostatic charge

repulsion of the polar head groups and A G°,, is the

free energy change related to the hydration of the

polar groups at the micelle-water interface. In the

case of ionic micelles the term A G ° 0 will vanish and

the free energy is given as

AG" = AG°e +A G'w (8)

Structural Aspects of Surfactant Micellar Systems

Surfactant molecules can be considered as building

blocks. Their self-association in aqueous media is

strongly cooperative and starts generally with the

formation of roughly spherical micelles around the

critical micelle concentration. When the surfactant

concentration markedly exceeds the cmc, the shape of

13

the spherical or ellipsoidal micelle undergoes gradual

change^^'^^. Fig 1.5 schematically shows various

structures that are formed upon increasing the

concentration of surfactant. In the beginning of

structural changes, spherical micelles become cylindri­

cal . Further increase in concentration results in a

hexagonal packing of water cylinders. Upon addition of

an oil and a short-chain alcohol, one can convert such

water cylinders into water-in-oil (w/o) microemulsions.

It is possible to induce a transition from one

structure to another by changing the physico-chemical

conditions such as temperature, pH, addition of ionic

and nonionic solutes in the surfactant solutionis,66-

^2 , For ionic surfactant systems micellar growth

increases very strongly with decreasing temperature,

with increasing counterion size, and with addition of

salts^^"^^. For nonionic micelles, raising the

temperature favours micellar growth^^ The rod shape

structure fits the results for dimethyldodecylamine

oxide micelles in salt solutions at low pH values^^.

The shape and size of these micellar aggregates

can, in principle, be determined by various methods,

such as light scattering"73-75^ diffusion sedimentation

velocity, sedimentation equilibrium^e,77^ ultrasonic

u

i V

foctont Molecules Sphericoi Micelles

<a) ( b )

^ w,

Rod-shaped Mlctljcs

( C )

Lomellar Phote

( e )

Reverse Hexoyonoi Phose

( f )

Hexa9onoi Phose

( d )

Revtrse Micelles

(g)

1-5 : The order of phase s t ructures formed upon Increas su r fac tan t concen t ra t i on .

ing

21

absorption'^S^ time resolved fluorescence''^»^^^ etc. The

micellar sphere-to-rod transition is highly dependent

upon the nature of the counterions and it has been

concluded that strong counterion binding promotes the

transition from spherical to cylindrical micelles'^O» ^.

Transition of spherical to larger micelles for

ionic surfactants occurs upon a reduction of interhead-

group repulsion^^, 83 it may be caused by salt^^ or

surfactant^S,86 additions or solute solubiliza-

tion^5,46 It is not clear if, at fixed surfactant

concentration, micellar growth by increasing salt

concentration is because of enhanced screening of the

electrostatic interactions or due to change in

"electrical charge per head group".

Packing considerations constitute a factor which

involves the nature of the hydrophilic and hydrophobic

groups of the surfactant. A critical ratio (Rp) with

associated limits for several of the possible

aggregation shapes has been devised by Mitchell and

Ninham87^ defined as

Rp = VhMolc

where

Vji = the volume of the amphiphile's hydrocarbon tail

22

AQ = the optimum cross-sectional area per amphiphile

molecule, and

1(, = the length of the fully extended hydrocarbon tail.

The optimum cross-sectional area per amphiphile

molecule is observed experimentally by X-ray diffract­

ion of bilayer system while the volume and length of

the hydrocarbon tail may be calculated by Tanford^S

equations: Vji = (27.4 + 26.9n)A'»3

Ic = (1.5 + 1.265n)A''

(n is the number of carbon atoms in the hydrocarbon

chain).

Considering the geometric dimensions, the volume

and the surface area of each association structure

yield critical conditions for the formation of each of

the following shapes:

Spherical structures: Rp < 1/3

Cylindrical structures: 1/3 £ Rp £ 1/2

Bilayer structures: 1/2 ^ Rp < i

Inverted structures: ^p ^ 1

The V ^ / A Q I C ratio depends on the surfactant

chemical structure (1^ and Vji) and on surface

repulsions between head groups (AQ) . The desired

curvature (and thus type of aggregate) may be obtained

23

upon a correct choice of the surfactant molecule and

solvent conditions (type of solvent, ionic strength,

etc.) using the VJI/AQIJ, ratio as a guide (Fig. 1.6).

However, the ratio has to be used with caution as it

accounts only for geometrical considerations.

Larger, less curved or even reverse structures of

micelles are likely to be formed by amphiphiles with

smaller inherent head group area (high Rp). By addition

of a counterion or a suitable cosurfactant in ionic

surfactants, the same area-shrinking effect may be

achieved. Lengthening or unsaturation of the

hydrocarbon chain, particularly cis double bond, leads

to larger structures. In three and four component

systems, by using this packing ratio, Fang^^ explained

a series of phase transitions (starting with normal

micelles and ending with reverse micelles). The surface

area occupied by the surfactant's polar head group

should be large to form a spherical structure. If the

heads are permitted to pack tightly, on the other hand,

the aggregation number will increase and rod and disk-

shaped micelles be favoured. The essential considerati­

on pertaining to the area occupied by the heads is the

work necessary to overcome the electrical repulsion

experienced by heads of like charge. A surfactant

24

Vh/Ao^c Aggregate shape Type of

sur fac tant

1/3 X Y

1/2 X X

• >

Spherical mfcelles

Single chain

Ionic or zwltterionlc

/ - N Cylinders }(that

• - ^ may be flexible)

Single chain Non-ionic or ionic wi th added salt

Flexible lamella ve­sicles

!V!i Lamellar phases = ^ ^ ^ Reverse ^ ^ «-- micelles -G'*)^ (in apolar

so lvents)

Double chain

Double chain Small area per headgroup

Fig. 1*6; Schematic diagram of possible aggregate shapes according to the V , / A Q I C

criterion .

25

c a r r y i n g a l a r g e charge on a r e l a t i v e l y smal l charge-

b e a r i n g atom w i l l i n h e r e n t l y be more a p t t o form

s p h e r i c a l m i c e l l e s because of the h igh energy needed t o

overcome t h e p r o h i b i t i v e charge d e n s i t y of t he head

group. A s u r f a c t a n t wi th a high degree of coun te r ion

b ind ing may overcome head group r e p u l s i o n by ho ld ing

the o p p o s i t e l y charged coun te r ions between head groups

of s i m i l a r cha rge , and hence head group r e p u l s i o n i s

r e p r e s s e d and rod o r d i s k - s h a p e d m i c e l l e s become

favoured.

Effect of Additives on Growth Processes

An i n t e r e s t i n g aspect of the mice l l a r so lu t ions i s

tha t they show a large change in v i s c o s i t y on adding

i n o r g a n i c s a l t s o r o r g a n i c c o s u r f a c t a n t s which

i n d i c a t e s t h e growth of t he m i c e l l a r a g g r e g a t e s ' ^ ' ^ ^ ' ^ ^

The growth of m i c e l l e s from s p h e r i c a l shape t o rod l i k e

i s of g r e a t expe r imen ta l and t h e o r e t i c a l i n t e r e s t .

(a) Effect of Sa l t s

Inorganic s a l t s are usual ly used as thickening

a g e n t s f o r c o n c e n t r a t e d s u r f a c t a n t s o l u t i o n s . The

presence of s a l t ions near the p o l a r heads of the

s u r f a c t a n t m o l e c u l e s d e c r e a s e s t h e r e p u l s i o n f o r c e

be tween t h e head g r o u p s . T h i s r e d u c t i o n i n t h e

2B

repulsion makes it possible for the surfactant

molecules to approach each other more closely and form

larger aggregates which requires much more space for

the hydrophobic chains. There are at least two factors

responsible for determining such a transition of

micellar shape in presence of salts. One is the

electrostatic effect of simple salts due to the

counterion binding on ionic micelles, and the other is

the hydrophobic interaction between surfactant

molecules or ions caused by the change in the hydrogen

bonded structure of water. Many workers have discussed

the effects of inorganic salts on ionic surfactant

solutions in terms of electrostatic interactions, ionic

hydratability, changes in the water structure, etc.,

and have classified ions as water structure breakers

and promoters^O"^^.

Aggregates with charged surfaces bind counterions

selectively, and their solution properties such as

aggregates size and shape, phase stability, the binding

of ions and molecules, and their effects on the rates

and equilibria of chemical reactions are sensitive to

counterion concentration and type9^"104 Counterions

are "bound" primarily by the strong electrical field

created by the head groups but also by specific

27

i n t e r a c t i o n s t h a t depends upon head g r o u p s and

coun t e r i on t y p e . M i c e l l a r shapes should be determined

under the exper imenta l c o n d i t i o n s because t h e s e a r e

s e n s i t i v e t o s u r f a c t a n t c h a i n - l e n g t h , head g roup

s t r u c t u r e and coun te r ion type^^ ,96 ,98 ,100 ,105^ S p e c i f i c

c o u n t e r i o n e f f e c t s on a v a r i e t y of m i c e l l a r s h a p e s

g e n e r a l l y fo l l ow a H o f m e i s t e r s e r i e s ^ 2 ^ i . e . , f o r

c o u n t e r i o n s of the same v a l e n c e , the s i z e of t he e f f e c t

i n c r e a s e s wi th coun te r ion s i z e ( c r y s t a l r a d i u s ) and the

e a s e of d e h y d r a t i o n of t h e c o u n t e r i o n ^ O l , 1 0 5 - 1 0 8

However, s p e c i f i c i t y may a l s o depend upon hydrogen

bonding i n t e r a c t i o n s between hydra ted c o u n t e r i o n s and

head groups or the p a r t i a l d i s r u p t i o n of t h e h y d r a t i o n

l a y e r s of the head groups and c o u n t e r i o n s , and the

p o s s i b i l i t y t h a t a f r a c t i o n of t h e c o u n t e r i o n s a r e

sitebanmrfl to surfaccttaaitt head grou^„ e.g., contact ion

p a i r formation, cannot be excluded.

Ikeda and c o - w o r k e r s ^ 0 9 have shown by means of

l i g h t s c a t t e r i n g t h a t t h e m i c e l l e s of SDS and

dodecyldimethylammonium c h l o r i d e change s h a p e from

s p h e r i c a l t o r o d - l i k e when the c o n c e n t r a t i o n of added

NaCl exceeds , r e s p e c t i v e l y , 0.45 M and 0.80 M. Such an

e f f e c t of added NaCl on t h e SDS m i c e l l e was a l s o

observed by Mazer and co-workersHO. H I by measurements

28

of quasi-elastic and total intensity light scattering.

Corti and Degiorgio^^^'^^^ also observed large values

of aggregation number and hydrodynamically equivalent

radius of the SDS micelle in 0.6M NaCl by using the

same techniques.

The aggregation of surfactants in a lamellar array

can be facilitated if one of the following requirements

is met. First of all, a high surfactant concentration

in water often leads to a lyotropic lamellar liquid

crystalline phase. Numerous phase diagrams can be

listed, where, as a function of composition and/or

temperature, a lamellar phase is observed^^»^^^.

Double-tailed amphiphiles usually form bilayer sheets,

as their most hydrated state allows the molecules to

pack only in a lamellar arrangement. Upon closing, the

bilayers form vesicles^^^"^^^. Lamellar aggregates are

also formed from delicate mixtures of anionic and

cationic surfactants in water^^ or mixtures of ionic

surfactants and long-chain alcohols in waterl20 ©r

electrolyte solution^^l. Some surfactant molecules in

aqueous solution are spontaneously transformed from

micelles into a lamellar array in the presence of a

high salt concentration. On a molecular scale, this

change in aggregate morphology is facilitated by an

29

increase in counterion binding and dehydration of the

surfactant head groups and bound counterions. On a

large scale, interactions between lamellae occur,

leading to the formation of either unilamellar vesicles

(small or large) or multilayered systems (oligo-and

multilamellar vesicles, lamellar droplets, or a

continuous lamellar phase, L ) . The induction of a

lamellar arrangement of surfactant molecules by salts

finds an important commercial application in liquid

laundry detergents^22-125

(b) Effect of Nonpolar Additives

Smith and Alexanderl26 recorded the sedimentation

patterns of micellar solutions of cetylpyridinium

chloride containing various amounts of tri-chlorobenze-

ne, toluene or methylcyclohexane in the presence of

sodium chloride. They concluded that, at concentrations

below the observed viscosity maximum, the addition of

an aromatic solubilizate promoted the formation of long

rod-shaped micelles leading to increased viscosity. At

higher solubilizate contents they found evidence for

the appearance of more compact micelles which could

account for the decreasing viscosity.

Gotz and Heckmann^27 studied conductivity

30

anisotropy of concentrated CTAB solutions (0.30-0.57M).

They concluded that the CTAB micelle is anisotropic

even in the absence of additives and, furthermore,

solubilization of small amounts of benzene greatly

enhances the apparent micelle length. Reiss-Husson and

Luzzati^28 studied the structure of micellar solutions

of several amphiphilic substances by means of X-ray

diffraction. They could conclude that the micelles in a

pure CTAB solution at 27°C are rod-shaped when the

concentration is larger than 5% by weight.

Eriksson and Gillberg^29 have determined resonance

line shifts and relative line widths of CTAB hydrogens

and aromatic solubilizate hydrogens at several

solubilizate concentrations in 0.1729M CTAB solution.

The results indicate that for benzene, N,N,-

dimethylaniline and nitrobenzene, the predominating

solubilization mechanism at low and intermediate

solubilizate concentrations involves adsorption at the

micelle-water interface whereas isopropylbenzene and

cyclohexane are preferentially solubilized in the

hydrocarbon part of the micelle. The phenomenon of

solubilization of aromatic compounds by adsorption at

the micelle-water interface can be understood on the

basis of thermodynamic arguments. In the pure water-

31

micellar solution some water molecules penetrate into

that hydrocarbon part of the micelle which is close to

the polar heads. It is certainly favorable from an

energetic point of view that an aromatic, like benzene,

N,N-dimethylaniline, or nitrobenzene, is substituted

for this penetrating water because of the high

polarizability of the aromatic ring and the bonding

abilities of the substituent groups. Thus, by this

adsorption the system can lower its energy in

comparison with the case of an even distribution of

aromatic molecules within the micelle, and the energy

difference in question may more than compensate the

associated diminution of entropy. In the case of

isopropylbenzene it is not likely that the same

solubilization mechanism is so effective because of the

presence of isopropyl group which counteracts the

effect of the aromatic ring. Instead, dissolution of

isopropylbenzene in the central part of the micelle

appears to be energetically advantageous, implying that

the particular interfacial structure which promotes a

more well-ordered micelle state is never created. This

solubilization in the centre of the micelle might

involve a reorganization of the micellar structure so

that a more spherical micelle is obtained instead of

32

the postulated original rod-shaped micelle.

For micelles to maintain a spherical form some of

the tails must be able to reach the centre of the

micelle. Since there can be no vacuum at the centre of

the micelle, the structure must rearrange into a rod

like shape when the micellar size places an undue

conformational stress on the surfactant tails to reach

the centre. Addition of an aliphatic hydrocarbon,

generally thought to reside in the micellar core,

relieves this requirement. Now the association

structure can maintain spherical form containing the

solubilized oil at a radius which was previously

prohibitive. It is in this manner that the aliphatic

hydrocarbons retard the sphere-to-rod transition.

Aromatic additives clearly behave differently in

the cationic surfactant system than they do with

anionic ones. Aromatic hydrocarbons stimulate rod

growth in case of cationic surfactants which may stem

from interaction of the delocalizedTV-electron cloud of

the benzene ring with the positive charges of the

surfactant head groups; a behaviour very similar to

that of a cosurfactant or counterion. The resulting

reduction of head group repulsion favours rods by

shrinking the surface area occupied per amphiphile.

33

thereby allowing the aggregation number to increase.

The apparent increase of rod promotion with longer side

chains on benzene emanates from the increase of

aggregation number associated with an increase of

radius. The effect of branching on the alkyl chain is

to add surface area to the micelle without appreciably

affecting its volume, drastically reducing the ability

of the additive to promote rod like micelles relative

to its straight-chain analog.

Benzene, toluene and ethylbenzene show a slight

tendency to destabilize sphere in SDS micelles, then

there is a trend towards increasing stabilization of

the spherical form with subsequent methylene additions

to the side chain. With propyl and butylbenzenes, the

micelles are able to retain spherical form at

concentrations of pentanol beyond the spherical limit

in the non-additive case. These results suggest that

the TV -electrons of the benzene ring do not have as

strong an effect when positioned at the anionic SDS

micellar surface as in the cationic tetradecyltrimethyl

-ammonium bromide (TTMAB) case With increasing length

of the alkyl chain, the aromatic molecules act more

like a saturated hydrocarbon, with apparently a higher

preference for the centre of the micelle. Residence at

34

the micellar core then promotes the spherical form by

relieving the requirement of the surfactant chains to

reach the centre of the structure.

(c) Effect of Polar Additives

Aqueous micellar solutions are knovm to solubilize

water insoluble or slightly soluble organic compounds.

In fact, it has long been believed that microemulsions

could not be obtained in the absence of alcohols. From

a practical point of view, alcohols have been used in

tertiary oil recovery because they bring about a large

decrease of the viscosity of the micellar systems used

in this process^^^. Addition of hydrophobic con5)Ounds

resulted in a growth of the micelles and an increase in

the aggregation number just large enough to keep the

charge density constant^^l. Addition of alcohols

resulted in a decrease of the charge density in a way

that was a function of the mole fraction of alcohol in

the micelle but independent of which alcohol was

usedl32 Mukerjee^ proposed that an additive which is

surface active to a hydrocarbon-water interface will be

mainly solubilized at the micellar surface and will be

found to promote the sphere-to-rod transition. Longer

chain alcohols are found to enhance micellar sphere-to-

rod transitions^^'1^3"^3^.

3 r

However, amines are more surface active than

alcohols at the air-water interf ace^-^^. Also, C4 to C^Q

n-alkyl amines have been found to be solubilized in

micelles by electrostatic and hydrophobic effects, and

the amine group is left on the surface of the

micelle^-^^ .

Wormuth and Kalerl39 determined the hydrophilic

ranking of three different amphiphilic classes of

additives in terms of the partitioning behaviour

between miceUlaHrr and aquecnuus pseuodophases. They found

that primary amines are more hydrophilic than either

alcohols or carboxylic acids. The authors also noted

that amine hydrophilicity was lower than expected when

coupled with anionic surfactant. Lindemuth and

Bertrand^^ have observed that amines are more effective

in the SDS system than in the TTAB. This indicates a

specific interaction between the amines and the anionic

surfactant head group at the micellar interface. It was

further seen that the amine head group has the ability

to sit deeper in the SDS micelle, relieving the

requirement of the surfactant tails to reach the centre

of the micelle at a shorter alkyl chain-length of

additive. Similar effects were seen in cationic

surfactants with carboxylic acids. This supports the

3[i

idea^^O that a cosurfactant with the ability to bear a

charge opposite to that of the surfactant head group is

more effective at promoting sphere-to-rod transition

and has the ability to better penetrate the surfactant-

rich film separating the water and oil domains. Similar

effect was seen by Prasad and Singh^^l ^.n case of SDS

and CTAB micelles.

(d) Effect of Salts + Organic Molecules

Micellar growth is generally facilitated by

addition of eletrolytes and cosurfactants but Missel et

al. found that urea retards the growth of SDS micelles

in 0 . 8M sodium chloride^B , Low values of the mean

aggregation number (N) of SDS in aqueous solutions of

n-pentanol have been found in several

studiesl32,142,143 However, the addition of 0. IM NaCl

to solutions of SDS in pure water and to aqueous 0.2M

SDS+0.6M n-pentanol has been found to increase N from

65 to 93142,144 and from 47 to 197143^ respectively.

Thus a larger increase of N is observed in SDS + n-

pentanol "mixed micelles" upon addition of 0. IM NaCl

compared to pure aqueous SDS solution. It was reported

earlier that in micellar growth the presence of a salt

and an organic additive in the system produce favorable

37

conditions''*^'^^^ which does not exist in presence of

either the salt or the additive alone'^0 jj- ^as

further reported that much greater concentrations of

lithium chloride relative to NaCl are required to cause

sphere-to-rod transition (growth process) to occur at

similar concentrations of n-pentanol. The effectiveness

of cations in promoting this transition decreases in

the order K+>NH4+>Na+>Li+, which is the order of

increasing hydrated radius of ions or decreasing ionic-

crystal radius. This order was also observed by other

authors. Very recently, the sphere-to-rod transition

was studied in SDS/NaCl solution in presence of various

organic additives'*^.

Solubilization of organics in aqueous salt

solutions of surfactants could be useful in micellar-

enhanced ultraf iltration'^'^ . In this process, such

system is added to a polluted aqueous solution. The

surfactant is then mainly in aggregate form which can

solubilize the organic solute. Since the size of the

micelles is greater than that of the dissolved

organics, the micellar solution can be filtered with an

ultrafiltration membrane having pores small enough to

reject the aggregates containing the organic pollutant.

Viscoelastic Properties of Surfactant Solutions

Dilute solutions of ionic and nonionic surfact­

ants usually behave as Newtonian liquids with

viscosities only slightly greater than that of water.

In contrast to these simple fluids, there are

viscoelastic surfactant systems that are known to have

a more complicated rheological behaviour.

The term viscoelasticity denotes the simultaneous

coexistance of viscous and elastic properties. In all

materials which exhibit this phenomenon the particular

response of a sample depends upon the time scale of

observation. Under conditions where the experiment is

comparatively slow, the sample will appear to be

viscous rather than elastic. For very short times,

however, the elastic response is much higher than the

viscous drag. This property can be seen by simply

swirling the solution and visually observing the recoil

of air bubbles trapped in the solution after the

swirling is stopped. Usually the viscoelastic behaviour

is observed when a third component is added to a rather

dilute ( < 1% w/w) aqueous solution of an ionic

amphiphile.

The molecular constitution of viscoelastic gels is

customarily described in terms of three dimensional

33

networks which may have a transient or permanent

character. Such networks can be formed from long rod­

like micelles in aqueous solutions and rod-like

micelles with an aqueous core in organic solvents. The

networks have viscoelastic properties which can be

characterised by a shear modulus and a structural

relaxation time.

At higher detergent concentrations the solution

shows thixotropic behaviour that undergoes a decrease

in viscosity with time while it is subjected to

constant shearing. The apparent viscosity depends on

the shear time and on the shear rate used. The term

thixotropic is originally associated to an isothermal

reversible sol-gel transformation. The interactions

among the rod-like micelles lead to the formation of

a new structure, a gel state. A gel possesses

elasticity, that is if the gel is sheared to a small

extent a more or less permanent force exists tending to

restore the gel to its former state. The rheological

behaviour of the solution is, first of all, determined

by the strength characteristics of this gell49^ They

are manifested when the solution at rest is deformed.

The phenomenon of viscoelasticity is linked to

rod- like micelles that are present in solution when

the concentration of the detergent is higher than the

second critical micelle concentration (cmcll). Normal

spherical micelles were observed in these solutions

between the cmcl and the cmcll. Non-spherical rod- like

micelles were shown to exist at detergent

concentrations above the cmcll. The elasticity of the

solution that is observed seems to be linked to a

structural change in the solution that takes place if

the solution is sheared. In the newly formed structure,

the axis of the rods are aligned also. When the

shearing is stopped, the aligned axis is lost again and

the elasticity disappears. The decay of elasticity

proceeds with time constants that are orders of

magnitude longer than the orientation time of a

single rod. The value of cmcll in viscoelastic systems

is at least partially controlled by intermicellar

interaction energies and not only by the interaction

between monomers and micelles as in case of the cmcl.

These systems seem to be micellar systems with a built

in tendency to form rod-like aggregates as soon as the

detergent concentration is as high as the cmcl.

The viscoelasticity is manifested in a number of

other properties as, for example, a non-Newtonian^^^a

viscous behaviour and flow-induced optical

41

anisotropy^^^^. A typical property of this type of

surfactant solutions is the long-range spatial

correlations present in the system. It is also clear

that the solution have a memory that can last for

seconds. This suggests that a long range order is

present in the solution. Thus, in viscoelastic

solutions the micellar aggregates form a periodic

structure that extends over macroscopic

distances^^^'^^^. The presence of a long-range periodic

structure seems to be most plausible rationalization of

the viscoelastic behaviour of dilute amphiphile

solutions containing moderately large rod-shaped

micelles. The system is optically isotropic but when it

is mechanically perturbed in a shear gradient an

elastically deformed lattice is generated. When that

shear is stopped a recoil to the equilibrium

configuration occurs.

The phenomenon of viscoelasticity can be caused by

addition of specific additives to some surfactants.

Generally, three different types of added molecules are

known to give the above effect: a second oppositely

charged surfactant, organic counterions, and uncharged

compounds like esters or aromatic hydrocarbonsl52,153

Some common examples for surfactants that form gel-

42 l i k e so lu t ions are summarized in Table 1 .1 .

Most of the invest igated systems contain ca t ion ic

su r fac t an t s combined with d i f f e ren t types of anionic

coiui ter ions. According to the genera l ly agreed models,

t h e s t r o n g e l a s t i c f o r c e s a r i s e from m e c h a n i c a l

i n t e r f e r e n c e between e longa t ed , rod-shaped m i c e l l e s .

The added compounds can, hence induce sphere • rod

t r a n s i t i o n s . I t i s wel l known t h a t t h e shape of t he

m i c e l l e s depends s t r o n g l y upon t h e a c t u a l p a c k i n g

pa rame te r s i n the m i c e l l a r assembly. If t h e h y d r o p h i l i c

head group a t the m i c e l l a r i n t e r f a c e r e q u i r e s an a r ea

which i s l a r g e r than the cor respond ing c r o s s - s e c t i o n of

t h e p a r a f f i n c h a i n s t h e s y s t e m w i l l t e n d t o form

a g g r e g a t e s wi th convex c u r v a t u r e s . I f bo th a reas a r e of

t h e same s i z e , p l ana r s t r u c t u r e s a r e favored. Under

c o n d i t i o n s where the c r o s s - s e c t i o n of t h e head group i s

s m a l l e r t han the cor responding v a l u e of the p a r a f f i n

c h a i n , t h e system p r e f e r s t o form i n v e r s e s t r u c t u r e s

( m i c e l l a r a g g r e g a t e s i n o r g a n i c s o l v e n t s ) . In

s u r f a c t a n t s o l u t i o n s , t h e o c c u r r e n c e of g e l - l i k e

c o n s i s t e n c y depends s t r o n g l y upon t h e c h e m i c a l

s t r u c t u r e of the c o u n t e r i o n . The a d d i t i o n of d i f f e r e n t

t y p e s of molecules leads t o l a r g e d e v i a t i o n s of packing

p a r a m e t e r s . Many c o u n t e r i o n s and c o s u r f a c t a n t s a r e

43 Table 1.1

Surfactant Systems Exhibiting Viscoelastic Properties

Surfactant

Tetradecyldimethylaraine oxide

Tetradecyldimethylamine oxide

Ci4H29N+(CH3)2 CO2-

Cetylpyridinium chloride

Cetyltrimethylainmonium bromide

Cetyltrimethylammonium bromide

Cetyltrimethylatnmonium chloride

Cetyltrimethylammonium chloride

Cetyltrimethylammonium chloride

Cetyltrimethylammonium chloride

Cetylpyridinium chloride

Tetradecyltrimethylammonium bromide

C8Fi7S03Na

C9Fi9Co2Na

Cetyltrimethylammonium bromide

Cetyltrimethylammonium bromide

Cetylpyridinium chloride

Additive

Surfactant

Sodium dodecyl sulphate

C7Fi5C02Na

Sodium dodecyl sulphate

Na-salicylate

Salicylic and 3-,4-,5-Methylsalicylic acids

Na-salicylate

NaSCN

2-Aminobenzene sulphonate

Perfluorobutyrate

4-Methylsodium benzoate

2-,3-,4-Methyl, 4-Ethyl,4-Propyl & 4-Pentylsodium benzoates

Na-Salicylate

(C2H5)4NOH

(CH3)4N0H

Uncharged compound

Chloroform

1-Methylnaphthalene

4-Propylphenol

44

strongly adsorbed at the micellar interface: depending

on the amount of penetration, this may change the mean

distance between the polar head groups or increase the

cross-section through the aliphatic chain.

T^portance of Research Problem

Supramolecular aggregates ctnd assemblies such as

association colloids, vesicles, biological membranes,

monolayers, proteins, DNA, polyeletrolytes and ion-

exchange resins all share an important structural

feature: an interfacial region of moderate polarity

(similar to that of alcohol) juxtaposed to a highly

polar aqueous region. Aqueous solutions of ionic

micelles are attractive model systems for the

ion binding properties of the much more complex systems

of natural and synthetic liposomes and vesicles and

biological membranes.

The spontaneous association of a large number of

surfactant molecules (ions) to give a micelle in

aqueous solutions is often taken as a model for

hydrophobic bonding which is believed to be partly

responsible for the stability of the native state of

proteins and most likely must have been the first step

in the genesis of the living cell.

Many studies have focussed on the properties of

45

the water trapped in these structures, which can differ

considerably from those of "normal" water^^"*"!^^. These

peculiarities have prompted an increasing number of

studies on a variety of chemical^^''' ^^,

photochemical^^^ and enzyme-catalyzed^57,160 processes

in micellar systems. Some explorers have also searched

the possibility of using their water microdroplets as

"nanoreactors" of controllable size, allowing control

of the size of microparticles synthesized within

them^^^ and their applications for solubilization and

extractionl62 ^j-^ numerous.

The change in micellar structure have pronounced

effects on micellar catalysis^^^, Several reports on

the structure of micelles of CTAB have recently

appeared^^' ^ and this micelle has been used to

catalyse a variety of reactions^^^"^^^. The surface

active agents may influence the biological efficacy of

drugs or pesticides. Many poorly soluble drugs and

pesticides are administered in a solubilized form using

micellar solutions in order to increase the

bioavailability and targetting to the site of action.

Increasing attentions is being devoted to the

study of the "incorporation- or solubilization of

neutral organic molecules into micelles in aqueous

4G

solution. Some of the most studied solubilizates are

alcohols, amines, etc., because of the important role

they have in preparation of microemulsions^^^. It is

generally accepted that the medium chain-length

alcohols and amines intercalate between the surfactant

ionic head groups to decrease the micellar surface

charge density^^^,142 This effect is correlated with

modification of the growth and shape of the micelles^^.

Despite the significance of amines in microemulsions

proper attention has not been paid so far to the

contribution of medium chain normal amines in micellar

systems.

One other important application of the use of

surfactant SDS is routine in most biochemical

laboratories; this is polyacrylamide gel electrophore­

sis (PACK)) in SDS, i.e., SDS-PAGB. The technique is

used to determine the polypeptide composition of

proteins and depends on the formation of SDS-

polypeptide complexes.

Over the years several of the phase structures

produced by surfactants have been of interest to the

pharmaceutical scientist, either as drug vehicles/

carriers or more recently as targetting systems.

47

Brief description of the exact problem discussed in the

thesis

The preceding pa r t of the in t roduct ion shows that

the growth of the micel le in presence of s a l t only i s

an es tabl i shed f ac t . The s i t ua t i on i s not same with

o r g a n i c a d d i t i v e s a l t h o u g h t h e r e s e a r c h i s g a i n i n g

momentum i n t h i s d i r e c t i o n s i n c e l a s t two d e c a d e s .

There are very few studiLffiSB {supra vide) which were

d i r e c t l y c o n d u c t e d i n p r e s e n c e of b o t h s a l t s and

o rgan ic a d d i t i v e s . This t h e s i s i s e x c l u s i v e l y concerned

t o t h e v i s c o s i t y b e h a v i o u r of m i c e l l a r sys t ems

( c a t i o n i c s u r f a c t a n t s ) i n p resence of o rgan ic a d d i t i v e s

with and wi thou t s a l t s .

The t h e s i s comprises t h r e e more c h a p t e r s exc luding

t h i s i n t r o d u c t o r y p a r t . Chapter I I i s concerned mainly

with the r o l e p layed by d i f f e r e n t c l a s s of a l i p h a t i c

compounds and t h e i r comparison i n connec t ion t o the

flow b e h a v i o u r ( m i c e l l a r growth) of CPC m i c e l l a r

sys tems. The r o l e of a l i p h a t i c amines i n m i c e l l a r

growth i s f u r t h e r exp lored by t a k i n g ano the r c a t i o n i c

s u r f a c t a n t CTAB (Chapter I I I ) . The purpose of t he work

was t o c o l l e c t more d a t a i n p r e s e n c e of a l i p h a t i c

amines as such type of a d d i t i v e e f f e c t i s n e a r l y a

neg lec ted f i e l d . Such s t u d i e s may be u se fu l t o provide

4S

wide spectrum of additives which could be used for

micellar growth purposes.

Many counterions are strongly adsorbed at the

micellar interface: depending on the amount of

penetration this may change the mean distance between

the polar head groups or increase the volume of the

micellar core. From a chemical point of view, the

salicylate and alkyl benzoate counterions are more

efficient because they give the desired effects in the

highly dilute regime. It is not surprising, therefore,

that these particular counterions have been the subject

of numerous investigations. In order to get a deeper

insight to the complicated phenomenon of counterion

condensation, Chapter IV is devoted to different bulky

counterions (salicylate and benzoate anions) and their

effects are compared with few aromatic acids (salicylic

and anthranilic) which give anions similar as of these

salts.

43 Table 1.2

Names and Structural Fommlae of the Chemicals Used

Name Abbreviation Structural Formulae

1

2

3

4

. Cetylpyridiniuin Chloride

. CetyltrimethylammoniiHa bromide

.Alcohols (a) 1-Propanol (b) 1-Butanol (c) 1-Pentanol (d) 1-Hexanol (e) 1-Heptanol (f) 1-Octanol

. Amines (a) n-Butylamine (b) n-Hexylamine (c) n-Heptylamine (d) n-Octylamine

CPC

CTAB

C3OH C4OH C5OH CgOH C7OH CaOH

C4NH2 C6NH2 C7NH2 C8NH2

Q) CI N I CH2(CH2)i4CH3

CH3 (CH2) 15N+(CH3) 3Br'

CH3(C3l2)20H CH3(CH2)30H C H 3 ( a i 2 ) 4 0 H CH3{CH2)50H CH3(CH2)60H CH3(CH2)70H

CH3(CH2)3NH2 CH3(CH2)5NH2 CH3(CH2)6NH2 CH3(CH2)7NH2

0 ONO

5. Sodium salicylate

6. Sodium benzoate

7. Salicylic acid

8. Anthranilic acid

NaSal

NaBen

SA

AA

30

REFERENCES

1. G.S. Hartley, "Aqueous Solutions of Paraffin

Qiain Salts", Hermann, Paris, 1936.

2. J.K. Thomas, "The Chemistry of Excitation at

Interfaces", American Chemical Society,

Washington D.C., 1984.

3. W.L. Hinze, in "Colloids and Surfactants:

Fundamentals and Applications", Edited by E.

Burmi and E. Pelizzetti, Society Chimica

Italiana, Rome, pp. 167-207, 1987.

4. P.H. Elworthy, A.T. Florence and C.B. Macfarlane,

"Solubilization by Surface Active Agents and its

Applications in Chemistry and the Biological

Sciences", Chapman and Hall, London, 1968.

5. J.W. McBain, "Colloid Science", D.C. Heath and

Co., Boston, 1950.

6. K.J. Mysels, "Introduction to Colloid Chemistry",

Inter Science, New York, 1959.

7. M.J. Schick, J. Coll. Sci., 17, 801 (1962) .

8. M.J. Schwuger, J. Am. Oil Chem. Soc, 59, 258

(1982) .

9. J. Leja, "Surface Chemistry of Froth Flotation",

Plenum, New York, 1982.

10. R.H. Ottewill, in "Nonionic Surfactants", Edited

51 by M.J. Schick; Dekker, New York, 1967.

11. P. Mukerjee, in "Solution Chemistry of

Surfactants", Edited by K.L. Mittal, Plenum Press,

New York, 1979.

12. J.H. Pendler and E.J. Fendler, "Catalysis in

Micellar and Macromolecular Systems", Academic

Press, Inc., New York, 1975.

13. M. J. Schick, in "Nonionic Surfactcints Physical

Chemistry". Edited by M.J. Schick, Marcel Dekker,

Inc., New York, Vol. 23, 1987.

14. G.C. Kresheck, in "Water", Edited by F.Franks,

Plenum, New York, 4, 104, 1975.

15. E.D. Goddard and G.C. Benson, Canadian J. Chem.,

35, 986 (1957) .

16. K. Meguro, Y. Yakasawa, N. Kawahashi, Y. Yabata

and M. Ueno, J. Colloid Interface Sci., 83, 50

(1981).

17. R.F. Tuddenham and A.E. Alexander, J. Phys.

Chem., 66, 1839 (1962).

18. S.D. Hamann, J. Phys. Chem., 66, 1359 (1962).

19. P. Mukerjee and K.J. Mysels, "Critical Micelle

Concentrations of Aqueous Surfactant Systems",

NSRDS-NBS 36, Washington, D.C., 1971.

20. K. Shinoda, T. Nakagawa, B. Tamamushi and T.

52

Isemura, "Colloidal Surfactants: Some Physico.

Chemical Properties", Academic Press, New York,

1963.

21. B. Lindman and H. Wennerstrom, "Micelles", Topics

in Current Chemistry, Vol. 87, p. 5. Springer-

Verlag, Berlin/Heidelberg/New York, 1980; Y.

Chevalier cind T. Zemb, Rep. Prog. Phys., 53, 279

(1990) .

22. W. Marcel , P r o t e i n s : S t r u c t . Func t . Gene t . , 1,4

(1986) .

23. E.H. Cordes, Pure & Appl. Chem., 50, 617

(1978).

24. P. Fromjerz, Chem. Phys. Lett., 77, 460 (1981).

25. P.M. Menger and D.W. Dill, J. Am. Chem. Soc. 100,

1109 (1984) .

26. C.B. Macfarlane, Kolloid-Z.u.Z. Polym., 239, 682

(1970) -

27. G.W. Brady and M. Kaplan, J. Chem. Phys., 58,

3535 (1973) .

28. G.W. Brady, J. Chem. Phys., 58, 3542 (1973).

29. Yves M. Tricot, D.N. Furlong and W.H.F. Sasse,

Aust. J. Chem., 37, 1147 (1984).

30. J.H. Fendler, Ace. Chem. Res., 13. 7 (1980).

31. W.D. Weatherford, J. Dispersion Sci. Technol.,

53

6. 467 (1985) .

32. Ajay Kumar, Ph. D. Thesis, IIT, Kanpur (India),

1989.

33. C.W. Brown, D. Cooper and J.C.S. Moore, J.

Colloid Interface Sci., 32, 584 (1970).

34. M. Wentz, W.H. Smith and A.R. Martin, J. Colloid

Interface Sci., 29, 36 (1969).

35. H. Saito and K. Shinoda, J. Colloid Interface

Sci., 35, 359 (1971).

36. J.F. Yan and M.B. Palmer, J. Colloid Interface

Sci., 30, 177 (1969).

37. J.H. Fendler, E.J. Fendler, R.T. Medary and O.A.

El Seoud, J. Chem. Soc, Faraday Trcins. I, 69,

280 (1973); J. Phys. Chem., 77, 1432 (1973).

38. H. Hoffmann, H. Nusslein and W. Ulbricht, in

"Micellization, Solubitization, and Microemulsi-

ons". Edited by K.L. Mittal, Pleraum Press, New

York, Vol. I, p. 263, 1977.

39. P. Becher, in "Cationic Surfactants", Edited by

E. Jungermann, Marcel Dekker, New York, 1970.

40. J. Clint, J. Chem. Soc, Faraday Trans. I, 71,

1327 (1975) .

41. H. Lange and K.H. Beck. Kolloid Z.u.Z. Polym.,

251, 424 (1973) .

42. T. Nakagawa and H. Inoue, J. Qiem. Soc. Japan.,

78, 104 (1956) .

43. J.M. Corkill, J.F. Goodman and J.R. Tate, Trans.

Faraday Soc, SO, 986 (1964).

44. D.N. Rxibingh and T. Jones, Ind. Kng. Chem. Prod.

Res. Dev., 21, 176 (1982).

45. M.F. Emerson and A. Holtzer, J.Phys. Chem., 71,

3320 (1967) .

46. P. Mukerjee, J. Pharm. Sci., 60, 1528 (1971).

47. P. Mukerjee, J. Pharm. Sci., GO, 1531 (1971).

48. Qi. Durga Prasad, H.N. Singh, P.S. Goyal and K.

S. Rao, J. Colloid Interface Sci., 155, 415

(1993) .

49. P.M. Lindemuth and G.L. Bertrauid, J. Phys. Chem.

97, 7769 (1993) .

50. G. Nemethy and H.A. Scheraga, J. Chem. Phys., 36,

3382 (1962) .

51. H.S. Frank, Nat. Acad. Sci., Nat. Res. Counc.

Publ., 942, 141 (1963).

52. H.S. Frank, Fed. Proc, Fed. Amer. Soc. Exp.

Biol., 24, Suppl. 15, S-1 (1965).

53. J.L. Kavanau, "Structure and Function in

Biological Membranes," Vol. 1, Holden-Day, San

Francisco, California, 1965.

00

54. D.G. Hall and B.A. Pethica, in "Nonionic

Suractants", Edited by M.J. Schick, Marcel

Dekker, New York, Vol. 1, p. 534, 1967.

55. E.W. Anacker, in "Nonionic Surfactants", Edited

by M. J. Schick, Marcel Dekker, New York, Vol. 1,

p. 203, 1967.

56. J.M. Corkill and J.F. Goodmann, Adv. Colloid

Interface Sci., 2, 297 (1969).

57. C. Tanford, J. Mol. Biol., 61, 59 (1972).

58. C. Tanford, "The Hydrophobic Effect", John Wiley

and Sons, New York, 1973.

59. C. Tanford, J. Phys, Chem. , 78, 2469 (1974).

60. D. Attwood, P.H. Elworthy and S.B. Keyne, J.Phys.

Chem., 75, 2212 (1971).

61. P. Molyneirx and C.T. Rhodes, Kolloid, Z.u.Z.

Polym., 250, 886 (1972).

62. K.S. Birdi, in "Proc. International Conf. Colloid

Surface Science", Edited by E. Wolfram, Budapest,

pp. 473-479, (1975).

63. K.S. Birdi, in "Colloidal Dispersions and

Micellar Behaviour", Edited by K.L. Mittal,

A.C.S- Symposium Series No. 9, pp. 233-238, Amer.

Chem. Soc, Washington, D.C., 1975.

64. K.S. Birdi, in "Micellization, Solubilization and

5o

Microemulsions", Edited by K.L. Mittal, Plenum

Press, New York, Vol. 1, p. 151, 1977.

65. P. Kkwall, L. Mandell and P.Solyom, J. Colloid

Interface Sci., 35, 519 (1971).

66. R. Zana, S.Yiv, C. Strazielle and P. Llanos, J.

Colloid Interface Sci., 80, 208 (1981).

67. S. Yiv, R. Zana, W. Ulbricht eind H. Hoffmann, J.

Colloid Interface Sci., 80, 224 (1981). .

68. K.W. Herrmann, J. Phys. Chem., 68, 1540 (1964).

69. N.A. Mazer, and G, Olofsson, J, Phys. Chem., 86,

4584 (1982) .

70. V. Rajagopalan, P.S. Goyal, B.S. Valaulikar and

B.A. Dasannacharya, Physica B, 180 & 181, 525

(1992) .

71. L. Sepulveda and C. Gamboa, J. Colloid Interface

Sci., 118, 87 (1987).

72. P.H. Elworthy, Kolloid -Z., 203. 67 (1965).

73. D. Attwood, J. Phys. Chem., 72, 339 (1968).

74. P.H. Elworthy and C. McDonald, Kolloid - Z., 195,

16 (1965) .

75. H. Hoffmann, H.S. Kielman, D. Pavlovic, G. Platz

and W. Ulbricht, J. Colloid Interface Sci., 80,

237 (1981) .

P.G. Nilson, H. Wennerstrom and B. Lindman, J. 76

57

Phys. Chem., 87, 1377 (1983).

77. R.H. Ottewill, C.C. Storer and T. Walker, Trans.

Faraday Soc, 63, 2796 (1967).

78. J. Lang, A. Djavankht and R. Zana, J. Phys.

Chem., 84, 1541 (1980).

79. M. Almgren and Shanti Swarup, J. Phys. Chem., 87,

876 (1983).

80. P. Lianos and R. Zana, J. Phys, Chem., 84, 3339

(1980) .

81. G. Lindblom, B. Lindman and L. Mandell, J.

Colloid Interface Sci., 42, 400 (1973).

82. S.J. Candau, E. E rsch and R. Zana, J. Physique,

45, 1263 (1984) .

83. P.J. Missel, N.A. Mazer, M.C. Carey and G.B.

Benedek, in "Solution Behaviour of Surfactants",

Edited by K.L. Mittal and E.J. Fendler, Plenum

Press, New York, p. 373, 1982.

84. A. Khatory, F. Kern, F. Lequexix, J. Appel, G.

Porte, M. Morie, A. Ott and W. Urbach, Langmuir,

9, 933 (1993).

B.Y. Sheu, S.H. Chen and J.H. Huang, J. Phys.

Chem., 91. 1535 (1987).

V.Y. Bezzobotonov, S. Borpely, L. Cser, B.

Farago, I.A. Glandlain, V.M. Ostanevich and S.Z.

85

86

58 Vass, J. Phys. Chem., 92, 5730 (1988).

87. D.J. Mitchell and B.W. Ninham, J. Chem, Soc,

Faraday Trans. 2, 77, 601 (1981) .

88. C. Tanford, J. Phys. Chem., 76, 3020 (1972).

89. J. Fang and R.L. Venable, Article II, Ph.D.

Dissertation (J. Fang). University of Missouri-

Rolla, 1987.

90. C. Gainboa and L. Sepulveda, J. Colloid Interface

Sci., 113, 566 (1986).

91. M.U. Oto and R.L. Venable, J. Colloid Interface

Sci., 35, 53 (1971).

92. L. Hsiao, H.N. Dunning and P.B. Lorenz, J. Phys.

Chem., 60, 657 (1956).

93. J.N. Phillips, Trains, Faraday Society, 51, 561

(1955) .

94. H.S. Frank and W.Y. Wen, Discuss. Faraday

Society, 24, 133 (1957) .

95. E.R. Nightingale, J. Phys. Chem., 66, 894 (1962).

96. J.H. Fendler, "Membrane Mimetic Chemistry",

Wiley-Interscience. New York, 1982.

97. C.A. Bunton, F. Nome, F.H. Quina and L.S.

Romsted, Ace. Chem. Res., 24, 357 (1991).

98. J. Degiorgio and M. Corti (Eds.), "Physics of

Anphiphiles: Micelles, Vesicles and

Microemuls ions , " E l s e v i e r , TUnsterdam, 1985.

99. G. Cevc, Biochim. Biophys. Acta , 1031-33, 11

(1990) .

100. B. Lindman and H. Wennerstrom, Top. Current

Chem.,87, 32 (1980).

101. L.S. Romsted, in "Surfactants in Solution",

Edited by K.L. Mittal and B. Lindman, Plenum

Press, New York, Vol. 2, 1984.

102. H. C3iaimovich, F.M.V. Aleixo, I.M. Cuccovia, D.

Zanette and F.H. Quina, in "Solution Behaviour of

Surfactants: Theoretical etnd Applied Aspects",

Edited by K.L. Mittal and E.J. Fendler, Plenum

Press, New York, Vol. 2, p. 949, 1982.

103. C.A. Bunton and G. Savelli, Adv. Phys, Org. Chem,

22. 213 (1986) .

104. C.A. Bunton, in "Kinetics and Catalysis in Micro

heterogeneous Systems", Edited by M. Gratzel and

K. Kalyanasundaram, Marcel Dekker, New York,

1991.

105. P. Mukerjee, K.J. Mysels and P. Kapauem, J. Phys.

Chem., 71. 4166 (1967).

106. L.S. Romsted, in "Micellization, Solubilization

and Microemulsions", Edited by K.L. Mittal,

Plenum Press, New York, Vol. 2, p. 489, 1977.

CO

107. L.S. Romsted, Ph.D. Thesis, Indiana University,

1975.

108. C. Gamboa, L. Sepulveda and R. Soto, J. Phys,

Chem., 85, 1429 (1981).

109. S. Hayashi and S. Ikeda, J. Phys. Chem., 84, 744,

(1980). S. Ikeda, S. Ozeki and M. Tsunoda, J.

Colloid Interface Sci., 73, 27 (1980).

110. N.A. Mazer, G.B. Benedek and M.C. Carey, J. Phys.

Chem., 80, 1075 (1976).

111. C.Y. Young, P.J. Missel, N.A. Mazer, G.B. Benedek

and M.C. Carey, J. Phys. Chem., 82, 1375 (1978).

112. M. Corti and V. Degiorgio, Ann. Phys. (Paris), 3,

303 (1978).

113. M. Corti and V. Degiorgio, in "Solution Chemistry

of Surfactants". Edited by K.L. Mittal, Plenum,

New York, Vol. 1, p. 377, 1979.

114. P. Ekwall, in "Advances in Liquid Crystals",

Edited by G.H. Brown, Academic Press, New York,

Vol. 1, 1975.

115. F.B. Rosevear, J. Am. Oil Chem. Soc, 31, 628

(1954) .

116. B.W. Ninham and D.F. Evans, Faraday Discuss,

Chem. Soc, 81, 1 (1986).

117. D. D. Lark, J. Colloid Interface Sci., 124. 428

61

(1988) .

118. H. Hauser, Biochem. Biophys. Acta, 772, 37

(1984) .

119. E.W. Kaler, K.L. Herrington, A.K. Murthy and

J.A.N. Zasadzinski, J. Phys. Chem., 96, 6698

(1992) .

120. R. Strey, W. John, G. Porte and P. Bassereau,

Langmuir, 6, 1635 (1990); H. Hoffmann, C. Thunig,

U. Munkert, H.W. Meyer and W. Richter, Langmuir,

8, 2629 (1992).

121. P. Herve, D. Rovix, A.M. Bellocq, F. Nallet and T.

Gulik-Krzywicki, J. Phys. II, 3, 1255 (1993).

122. J.C. Van de Pas, Tenside, Surfactants, Deterg.,

28, 158 (1991) ; J.C. Van de Pas, and C. Bytentek,

Colloids Surf., 68, 127 (1992).

123. A. Jurgens, Tenside, Surfactants, Deterg., 23,

222 (1986).

124. A. Sein, J.B.F.N. Engberts, E. Van der Linden,

and J.C. Van de Pas, Lamgmuir, 9, 1714 (1993) .

125. J.C. Van de Pas, Ph.D. Thesis, University of

Groningen, 1993.

126. M.B- Smith and A.E. Alexander, Proc. 2nd Inter.

Congr. Surface Activity, London, p. 349, 1957.

127. K.G. Gotz and K.Z. Heckmann, Z. physik. Chem.

62

(Frankfurt), 20, 42 (1959).

128. F. Reiss-Husson and V.J. Luzzati, J. Phys. Chem.,

68. 3504 (1964) .

129. J.C. Eriksson and G. Gillberg, Acta Chem. Scand.,

20, 2019 (1966) .

130. M. Baviere, in "Effects des alcools sur le

diagrammee de phase des systems sauimire-

hydrocarbure-tensioactif", Institute Francais du

Petrole, Report ref. 26928, April 1979.

131. M. Almgren and S. Swarup, J. Phys. Chem., 86,

4212 (1982) .

132. M. Almgren and S.Swarup, J. Colloid Interface

Sci., 91, 256 (1983).

133. J.W Larsen, L. J. Magid and V. Payton,

Tetrahedron Lett., 29, 2663 (1973).

134. H. Hoiland, K. Veggeland and S. Backlund, in

"Proc. Int. Synp. Surfactants in Solution",

Edited by K.L. Mittal and P. Bothorel, Plenum

Press, New York, Vol. 4, p. 309, 1986.

135. T. Tominaga, T.B. Stem and D.F. Evans, Bull.

Chem. Soc. Jpn., 53, 795 (1980).

136. S. Backlund, H. Hoiland, O.J. Kvanmen and E.

Ljosland, Acta Chem. SccUid., Ser. A, 36, 698

(1982) .

63

137. S. Gupta and S. Sharma, J. Indian Chem. Soc, 42,

855 (1965).

138. T. Yamashita, H. Yano, S. Harada and T. Yasunaga,

J. Phys. Chem., 87, 5482 (1983).

139. K.R. Wormuth and E.W. Kaler, J. Phys. Chem., 91,

611 (1987) .

140. D. Nguyen and G. Bertrand, J. Colloid Interface

Sci., 150, 143 (1992) .

141. Ch. Durga Prasad and H.N. Singh, Colloids Surf.,

59, 27 (1991).

142. M. Almgren and J.E. Lofroth, J. Colloid Interface

Sci- 81, 486 (1981).

143. P. Lianos, J. Lang, C. Strazielle and R. Zana, J.

Phys. Chem., 86, 1019 (1982).

144. Y. Croonen, E. Gelade, M. Van der Zegel, M. Van

der Auweraer, H. Vandendriessche, F.C. De

Schryver and M. Almgren, J. Phys. Chem., 87, 1426

(1983) .

145. S. Kumar, Kirti and Kabir-ud-Din, J. Am. Oil

Chem. Soc, 71, 763 (1994).

146. S. Kumar, Kirti, K. Kumari and Kabir-ud-Din, J.

Am. Oil Chem., Soc, 72, 817 (1995).

147. J.F. Scamehom, S.D. Christian and R.T.

Ellington, in "Surfactant Based Separation

04

Processes", Edited by J.H. Harwell and J.F.

Scamehom, Dekker, New York, p. 29, 1989.

148. (a) S. Gravshott, Proceedings of the VII Inter­

national Congress of Surface Active Agents,

Moscow, 1976, Vol. 2 (II), p-906, 1978.

(b) S. Gravshott, in "Polymer Colloids", Edited

by R. Fitch, Plenum Press, New York, 1979.

149. C.F. Goodeve, Trans. Faraday Soc, 35, 342

(1939).

150. I.F. Efremov, Surface Colloid Sci., 8, 85 (1976).

151. I.F. Efremov auid O.G. Us'garov, Usp. Khim., 45,

877 (1976).

152. S. Gravshott; Proc. 6th Int. Congr, Surface

Activity, p. 807, 1973 f

153. A.J. Hyde and D.W.M. Johnstone, J. Colloid

Intrface Sci., 53, 349 (1975).

154. M. Wong, M. Gratzel and J.K. Thomas, J. Am. Chem.

Soc, 98, 2391 (1976); M. Wong, J.K. Thomas and

T. Nowak, J. Am. Chem. Soc, 99, 4730 (1977)..

155. E. Keh and B. Valeur, J. Colloid Interface Sci.,

79, 465 (1981) .

156. P.E. Zinsli, J. Phys. Chem., 83, 3223 (1983).

157. M.P. Pileni (Ed.), "Structure and Reactivity in

Reverse Micelles", Elsevier, Amsterdam, 1989.

65

158. L. Garcia-Rio, J.R. Leis, M.E. Pena and E.

Iglesias, J. Phys. Chem., 91, 3437 (1993).

159. P.L. Luisi and B.B.Straub, "Reverse Micelles",

Plenum, New York, 1984.

160. Y.L. Khinelnitsky, I.N. Neverova, V.I. Polyakov,

V.Y. Grinberg, A.V. Levashov and K. Martinek,

Eur. J. Biochem, 19Q, 155 (1990); R.M.D. Verhaert

and R. Hilhorst, Rect. Trav, Chim., Pays-bas,

110. 236 (1991) .

161. J.H. Fendler, Chem. Rev., 87, 877 (1987).

162. K.L. Mittal (Ed.) "Micellization, Solubilization

cind Microemulsions", Plenum, New York, Vol. 1,

1977.

163. C.A. Bunton, in "Reaction Kinetics in Micelles",

Edited by E.H. Cordes, Plenum, New York, 1973.

164. E.H. Cordes and R.B. Dunlap, Ace. Chem. Res., 2,

329 (1969).

165. G.J. Uist, C.A. Bunton, L. Robinson, L. Sepulveda

and M. Stam, J. Am. Chem. Soc, 92, 4072 (1970).

166. P.G. de Gennes and C. Toupin, J. Phys. Chem., BS,

2294 (1982) .

CHAPTER - II

EFFECT OF ALIPHATIC ALCOHOLS/AMINES AND

TEMPERATURE ON THE MICELLAR GROWTH OF

CETYLPYRIDINIUM CHLORIDE MICELLES IN THE

PRESENCE AND ABSENCE OF POTASSIUM

CHLORIDE

67

In the recent past, numerous experimental

evidences on the existence of large elongated micelles

have been gathered. The roughly spherical ionic

micelles formed at the cmc can grow on reduction of

inter-head group repulsion^. Generally, this is

achieved by the appropriate conditions of

concentrations, salinity, temperature, presence of

counterions, etc.2/3 Recently, it has been demonstrat­

ed that not only inorganic salts but a few organic

con5)ounds such as n-alcohols^, n-amines^'^, and

aromatic hydrocarbons^, etc., are also potential

candidates for such structural changes.

A large body of work is available on

solubilization of orgctnic compoiuids by surfactant

micellesS"12 but structural changes produced by such

additives have not been studied in much detail^'^3-15

Solubilization results of polar organic molecules are

consistent with other physical evidences indicating

that these molecules have their head groups anchored in

the polar/ionic outer region of typical ionic

surfactants. Such molecules tend to solubilize at least

partly within the hydrocarbon core of the micelle,

although steric and substituent group effects may play

important roles in modifying the structure and

6;>

thermodynamic properties of the "intramicellar

solutions" of the organic solute in the micelles.

There has been considerable discussion in the

literature about the location of organic solutes in

ionic surfactant micelles. Various types of physical

evidences have been given to support claims that

benzene solubilizes primarily in the surface region of

the micelle^^, or primarily within the micellar

interior^'' or in both states^^. The aromatic

hydrocarbons are intermediate in behaviour between

moderately polar solutes {e.g., hydroxy substituted

benzoates, organic acids, amines, medium chain

alcohols, etc.) which are clearly intercalated in the

micelle surface region, and aliphatic hydrocarbons

which preferentially solubilize in the micellar core

regionl^ _

Gomati et al.20 have studied the phase diagram of

the ternary system cetylpyridinium bromide or chloride-

hexanol-brine. The studies provide evidence of the

determinant influence of the hexanol to surfactant

ratio on the structure of phases. The differences

observed in the two systems are related to the

different counterions. Experimental results of Porte et

al.21-24 reveal that elongated micelles are formed in

69

dilute solutions of cetylpyridinium salts in brine.

Evidence is provided that the micelles are indeed very

long cind are flexible cylindrical aggregates; their

lengths depend largely on the nature of the counterion

or concentration of electrolytes25,26, in contrast, the

addition of non-aromatic solubilizates to ionic

surfactants [(e.g., methyl cyclohexane^^ to cetylpyrid­

inium chloride-NaCl) ] have only a modest effect on

micelle aggregation numbers or solution viscosity^.

Due to unique solubilization properties, the

micellar systems have several applications; thus a

careful investigation of such properties is of

paramount interest. Organic components are common

pollutants in ground water and aqueous industrial

process streams^S. Micelle-enhanced-ultrafiltration

(MEUF) is a technique which could be used to remove

organic pollutants^^. If micellar size could be

increased by any means then it will be easier aind of

great help to decide the pore size in MEUF. This

observation is of practical iii5)ortance, since it is

directly related to the cleaning action for aquatic

environment. Therefore. a micellar growth study in

presence of salts and organic additives has relevance

with real world problem.

70

The site of solubilization of different compounds

within micellar systems can be correlated with the

structured organization of aggregates. Solution

viscosity responds to morphological changes of

aggregates cuid their mutual interactions. Micellar

growth is accotr ianied by a distinct rise in viscosity^

which can be connected to anisotropic

susceptibilities-^^.

The study aims to see the effect of organic

molecules on the growth of CPC micelles in aqueous or

aqueous-salt (O.IM KCl) solutions. For this purpose

viscosity measurements were performed at different

ten5)eratures.

B-irp«>T-iiii*»Tit-a1

CPC (Sigma, St. Louis) was recrystallized twice

from an ethanol-ethylacetate mixture and dried at 60°C

under moderate vacuum. The purity of CPC was ensured by

the absence of minimum in a plot of surface tension vs.

logarithm of concentration. Potassium chloride (purity

> 99%) was from B. Merck (India) while all alcohols (1-

propanol, C3OH; 1-butanol, C4OH; 1-pentanol, C5OH; 1-

hexanol, CgOH; 1-heptanol, C7OH and 1-octanol, CeOH)

were BDH (Poole, England) *high purity' chemicals and

were used as supplied. The amines (n-butylamine, C4NH2;

7i

n-hexylamine, C6NH2; n-heptylamine, C7NH2 and n-

octylamine, C8NH2, all 'purum grade') were obtained

from Fluka (Buchs, Switzerland) . Water was distilled

twice over alkaline KMn04 in an all-glass still.

The viscometric measurements were carried out by

using a Ubbelohde viscometer thermostated at fixed

teirperatures (25, 30, 35 or 40°C, accuracy: ± 0.1°C).

At higher additive concentrations, the viscosities were

dependent on rate of flow. To obtain viscosity values

under Newtonian flow conditions^!, ^ wide U-shaped tube

containing having water was connected a branch of the

viscometer. This arrangement allowed us to vary the

pressure (P) under which the solution flows and thus to

determine viscosity values at various rates of flow

from the slope of the straight lines P vs. l/t

(according to the Poiseuille equation equation: P=ii x

Ax l/t, where t is the time of flow of the solution in

a given viscometer, A is the characteristic constant of

the viscometer obtained by calibration with liquids of

known viscosities, and i is the viscosity of the

solution). Relative viscosities of solutions,

i\r<=Vlo)' were obtained by the ratio t/tg, (where tg

is the flow time for the solvent and T\Q its viscosity) .

Density corrections were not made due to their

11 insignificant effect on overall viscosity of the

solutions. The solvent flow-time in the viscometer was

always longer than 200s and no kinematic corrections

were introduced^^ At least four flow-time measurements

were made at each concentration and a mean deviation

from the mecin of all measurements not exceeding 0.1s

was required.

Results

All the viscosity experiments were performed with

aqueous micellar solutions of 0.2M CPC (this concentra­

tion is well above the cmc- ) with and without added

0. IM KCl. The data obtained by adding alcohols and

amines at different tenperatures {25-40°C) are compiled

in Tables 2.1-2.16. Some representative curves of

viscosity variations at 25°C are shown in Figs. 2.1-

2.4.

Discussion

From Figs. 2.1-2.4 it is clear that lower chain-

length additives {e.g., C3OH, C4OH or C4NH2) have

marginal effect on the viscosity of 0.2 M CPC micellar

solutions which remain nearly the same even in the

presence of O.lM KCl. These additives are mainly

hydrophilic molecules with excellent solubilities in

water and very little into micelles. They will not

/3

e

\n

(d n H

0 V H (d

r4

0

V4

CQ 0) •H i U •H «] 0 U CQ

•H >

> •H

Id H «

1 H 1 Q 1

IS. 1 JJ 1 U 1 O 1 1 1 H

1 H 1 0 1 CI 1 n 1 j j 1 a 1 0 1 W 1 1 1 H

1 H 1 0

!S : ^ 1 a 1 1 1 H

1 H 1 0

1§ 1 JJ 1 fl 1 OJ 1 04 1 1 1 H

1 H 1 0

1§ 1 4J 1 3 1 BQ 1 1 1 H

1 H 1 0

: § < a 1 0 1 M 1 a* 1 1 1 H

^ ' C 1

, 1

a 1 U 1 C - - 1 oz: 1

U ^ 1

U 1

cr 1 • 1

a 1 U 1 fl*- 1 O S 1 U ^ 1

» ^ 1

cr 1 , 1

a 1 U i C ^ 1 O S 1

U ^ 1

1 U 1 1 C 1

1 * 1 1 a 1 1 V 1 1 C ' - 1 1 O S 1 1 U - - 1

M 1 1 cr 1

, 1

fl 1 U 1 C - - 1 O S 1 U ^ 1

U 1 C 1

• 1

C 1 U 1 C - - 1 O S 1 U ^ 1

m <ND

m 00

H CTi

o **

-0

Jp u

o o

LD

O o

o H

00 00

o LD

n g

o o o

in y>

H

O o o

Ln U3

in o o

^ CO

H

tn o o

u> r»

f* o o

00

o « (N

O H

O

H cn

en o o

(N OS

'^

IT) H

O

cn (N

O H

O

O ^

« H

C H

O

(N I f l

-0 • H

^ M

S

00 H

o

o 00

-0 •H i3 M

(N CN

o o o

in vc

o H

O

00 p*

in H

o

in 00

o fS

o

^ (N

LD M

O

O P*

o n o

CNJ 00

m n o

in in

-0 • H ,Q M

(N ro

O m

o in

10 o o

in o H

M CN

O O

o m

O m CN

m

H

o o

n 00

H

O

m

o\ 00

H

O m

00

( N

O O

O

n

o o

m

(N

m in in

M

74

u e O ro a Id

n

H

0

u H (d

IH 0

#

CO 0)

•H

•H n 0 u n •H >

s •H Id H «

i H 1 0

: S 1 4J 1 U 1 O 1 1 1 H

1 H 1 0

1 4J 1 a 1 (U 1 K 1 1 1 H

1 0

: § IS 1 a 1 1 1 H

1 iH 1 0

IS 1 i J 1 C 1 (U 1 04 1 1 1 H

1 H 1 0

1§ 1 JJ 1 3 1 CQ

1 H

1 H 1 0

\% 1 a 1 0 1 U 1 04 1 1 1 H

^ i , 1

ti 1 0 1 ti-^ 1 O S 1 U ^ 1

^ • 1

C 1 U 1 C ' - 1

1 o s : 1 U — 1

i ^ i 1 • 1 1 C! 1 1 O 1 1 C^ 1 1 O S 1 1 U — 1

\ ^ 1 • 1 1 C 1 1 O 1 1 d - - . 1 1 O S 1 1 U ^ 1

1 U 1 1 c r 1

, 1 C 1

1 U 1 1 ti^ 1 1 O S 1 1 U - - 1

U 1 cr 1

• 1

C 1 V 1 ( 3 — 1 O S 1 U — 1

ro

o o

o o

H 00

o

CO

o

00

o

o H

M t

o

'J'

n

IT) H H

m 1 ^

If) >

in 00

vo H

in N

a\ \o

(N M

o o o

H

o o o

ro

o H o

rM

H

O H O

CO

in H

o

00

H

o ro

O

ro o

o

O

H

(N

O in

o

00 H

in

O

o in ro

o

\0 in

o ro

o

•01

o o H

00 ro

m

in

H

(N (N rv)

o o o

ro

H

o o

o

o

H 00

H

O in

o o H

ro CO

H

o m

o m H

H ro

CN

o o

o in CM

ro 00

fS

o o

M

75

1 H 1 0

: § 1 4J 1 U 1 O 1 1 1 H

1 H 1 0

1 4J

1 a 1 0 1 a 1 1 1 H

1 H 1 0

1 : S 1 a 1 1 1 H

1 H 1 0

: § 1 XJ 1 G 1 OJ 1 & 1 1 1 H

1 H 1 0

; s 1 j j 1 3 1 CQ 1 1 1 H

1 H 1 0

1 a 1 0 1 I U 1 CU 1 1 r 1 1 H 1

^ !

, 1 C 1 U 1 C ^ 1 O S 1 U ^ 1

^ > 1 C i U 1 fl-. 1 O S 1 U ^ 1

U 1 c 1 , 1 C 1 U 1

1 C — 1 1 O S 1 1 U — 1

1 U 1 cr" 1

1 ' 1 1 C 1 1 U 1 1 a^ 1 1 O S 1 1 U ^ 1

U 1 C 1

, 1 d 1 U 1 fl-- 1 O S 1 U ^ 1

^ • 1 C 1 U 1 C-- 1 O S 1 U ^ 1

o 1.0

o o

o

o o

o

o o

o

o o

o

o

o H

O 00

o If)

If 00

o

o

o H

H

(N

o

00 o

t^ ^

n in

H

n

H

n o

CN ro

o o

o

H

O

o

H 00

H

o in

H O

fN

O

o

H

M

O

in

(N

O in

H 00

o

CN

(N

vo

( \ <N

O O

O O

(N m

o o o

o

o H

O

H

If) H

O

O CO

o CN O

n H

in CN O

00

n

o

o

00 CM

rn o

o o

in

CN in

78

u e O

V Id

5 0 u H rO

d

+

s

IM 0

u

m 0)

•H

•H (Q 0 u n •H >

0 •

•H

10 H 0)

1 H 1 1 0

!S 1 4J 1 V 1 O 1 1 1 H

1 H 1 0

IS 1 U 1 CU 1 Q) 1 S 1 1 1 H

1 H 1 0

IS :S 1 » 1 1 1 H

1 H 1 0

1 4-) 1 a 1 0) 1 04 1 1 1 H

1 H 1 0

!§ 1 4-) 1 3 1 CQ 1 1 1 H

1 H 1 0

IS 1 0^ t 0 1 M 1 CU 1 1 1 H

U 1 t r 1

, 1 C 1 U 1 fl^ 1 O S 1 U ^ 1

_h! ' C 1

1 1

C 1 U 1 C ' - 1 O S 1 U ^ 1

U 1 cr 1

* 1 1 C 1 1 U 1 1 C ^ 1 1 o s : 1 1 U ^ 1

\ ^ 1 • 1 1 C 1 1 V 1 1 1 3 ^ 1 1 O S 1 1 U - - 1

i ^ i 1 • 1 1 a 1 1 U 1 1 C - . 1 1 O S 1 1 U ^ 1

^ 1 1 1

a 1 U 1 fi-. 1 O S 1 U - - 1

in

o o

a\ in

o o

o o

o o

in o

in o

o H

O in

H CO

o

00

o H

H

o

o CD

(N n

in H H

o\ in

H

c* LD

r* H ffi

fM O

m c\

M n

in H

o in

fN CN

o o o

m

o in o

00

o o H

o in H

H

o m CN

H

n CM

O in

o o tN

O O

o

m H

o o

o

cri m

00

H

o H

O

CTi

H

o

o

o (N

O

m o

H

m H

n

o

in

in o

' t

o o H

CM CO

^

i n

H

77

U a in <N

(6

0) H

0 u H 10 I d

H

u

o + u e

0

0) • H JJ • H CQ 0 U ta >

•H

«0 H

1 H 1 0

iS 1 Jj 1 O 1 O 1 1 1 H

1 H 1 0

l § 1 JJ 1 Cu 1 (U 1 » 1 1 1 H

1 H 1 0

: ^ : S 1 a 1 1 1 H

1 H 1 0

iS 1 4J

1 a 1 (U 1 04 1 1 1 H

1 H 1 0

i§ 1 iJ 1 S 1 m 1 1 1 H

1 H 1 0

IS 1 (X 1 0 1 U 1 Cl4 1 1 I H

# i C* 1 U 1 C - - 1 O Z 1

U - - 1

U 1

cr 1 • 1

C 1 0 1

1 C * - 1

1 OS : 1 U - ^ 1

1 U 1 1 e r ' 1

1 * 1 1 C 1 1 O 1 1 G-^ 1 1 0 £ 1 1 U ^ 1

1 U 1 I C 1

1 * 1 1 d 1 1 V 1 1 d - . 1 1 O S 1 1 U > ^ 1

1 U 1 1 PT' 1

1 C 1 0 1

1 C ! - - 1 1 O S i 1 U ^ 1

^ I • 1

C 1 U 1

fi— 1 OS 1 U ^ 1

o ^ H

o o

o

o ^

(N P>

• H

in o

o

n 5i<

H in

1

in

r o

o

n vo

vo ^ •

r H

00 o

o

H m

H CN

• 00

r-

0^ o o

H

«

00

m •

vc in n

H H o

o t

CN 00

• r» 00

p«

CN H o

H

• m

o o

• H O «(l< H

ro H o

• H

Xi u

-0 •rl i3 M e 'tf' H O

o o

o

o o

CO

in

o in

• o m o j3 [< N vo vo E

o n i n o > o ( N i n r * O O O O H H H H

o o o o o o o o -O

^ n fN f* O -rl o i n i n i n ' j * H 5 } < r o , Q ^ ^ 00 U

^ CO cft in 00 3 H H < f H ' * ' ( T i O O « > t - '

o « ) f s i n o L n p « o i n O O H H C N C N C S r O n

o o o o o o o o o -0 •H

t « > a i o o i . o n H f S »-i H H r n i n v o v o v o i n h

o H n ^ i n r » r > o c > j O O O O O O O H H

o r* ' t 00 ^0

^ VO CT> m CN

H H H fNJ ro

n CO

00 CO

o o

o m

CO

(N <N

•/..

r-k8o/ o o m

o fs n

78

1 H i 0

l § 1 V 1 U 1 O 1 1 1 H

1 H 1 0

! ^ 1 4J 1 Cl4 1 (U 1 a 1 1 1 H

1 H 1 0

; ^ 1 •>< 1 (U 1 a 1 1 1 H

1 H 1 0

i§ 1 iJ 1 a 1 (U 1 CU 1 1

1 H

1 H 1 0

IS 1 JJ 1 3 1 a 1 1 1 H

1 r-i 1 0

!§ 1 0^ 1 0 1 U 1 04 1 1 1 H

J ' C 1

, 1 C 1 U 1 C - - 1 0 2 1 U ^ 1

J ' C* 1

• 1

C 1 U 1 C ^ 1 O S 1 U - - 1

M 1 C 1

, 1 C 1 U 1 d ^ 1 O Z 1 U - ' 1

u \ C 1

• 1

C 1 V 1 C - - 1 O S 1 U — 1

U 1 ir 1

1 * 1

1 G 1 1 V 1 1 C ' - 1 1 O S 1 I U ^ 1

M 1 {It 1

• 1

a 1 1 U 1 1 C l ^ 1 1 O S 1 1 U — 1

'f ro

• H

o o o

<< ro

• H

O o o

'«< ro

• H

O o

ro U)

• H

LD O

O

(N ^

• H

ro o o

^ ^

• H

<o o

CTi o

• ro

r* o o

in in

•

H

Ln o o

o in

> ro

(N H

00 H

• o H

00 o o

r* (N

• ro

a\ o o

ro U3

1

00

in H

<N ro

• in ro

o o o

00 vc

•

o H

o H

O

o ro

t

in (N

O fS

o tn

• a\ ro H

H H

O

00 o

• 00 fM

CN H

O

^ m

• ^ \D

m (N

in ro

• o «£ ro

(N H

O

00 o

" "S* H ro

m H

o

u> (N

• O vo

c*-r

o o

• o ^ 00

ro H

o H H

• m H ' i *

p~ H

O

o 00

• H in

o ro

ro

O

o

ro

O

o

CO in

H

CM

H H (N

CO o

ro

o ro

m o

ro

ro 00

H

rs rj ro

o m O)

ro H

O o

in

H

O m

m 00

H

o o

ro fM

f^

o o

r>j

m o

o

m m m

V0

00

o o

M ro

79

u e m rn •U Id

n

H

0 u H Id

+ H U

IW

0

K 9)

•H 4J • H CQ 0 u n

>

• •H a Id H

1 H 1 0

i§ 1 i J 1 U 1 O 1 1 1 H

1 H 1 0

1 4J 1 & 1 0 1 W 1 1 1 H

1 H 1 0

: § !S 1 K

1 H

1 H 1 0

l § 1 i J 1 C 1 0) 1 P4 1 1 1 H

1 H 1 0

i ^ 1 U 1 3 1 CQ 1 1 1 H

1 H 1 0

: § 1 0 ^ 1 0 1 U 1 04 1 1 1 H

^ 1 1

a 1 0 1 d ^ 1 O S 1 U ^ 1

^ > 1

tf 1 U 1 C - - 1 O S 1 U ^ 1

^ 1 , 1

a 1 U 1 C - - 1 O S 1 U ^ 1

J^i 1 C 1

• 1 C 1 U 1 C — 1 O S 1 U ^ 1

• ^ i , 1

a 1 0 1 C ^ 1 O S I U - - 1

1 U 1 1 C 1

1 * 1 1 a 1 1 U 1 1 fl^ 1 1 O S 1 1 U ^ 1

n n

• H

O

o o

m n H

o o o

ro rn •

H

O

o

H VC

• H

in o o

H

^ H

ro o o

^ '*< •

H

V£ O

IT) <N

« n

r* o o

^ IT)

H

ID O

O

00 CO

•

(N

CM H

tn c ( V0

cs o o

t^ V£

(N

a\ o o

n r» • ID

m H

n in •

CO H

o o o

n CTi

V£

o H

O

n m •

^j* H

O (NJ

H M

• -<}* 00

H H

O

n ^ H

(N H

O

00 (N

• H ' i f

m <N

00 CTl

• 00

ro H

(N H

O

CTl

• ro ro H

m H

o

m t^ •

H

^

r* CN

V£> U)

1

o\ \o ro

ro H

o

ro •

CO CNJ

r* H

o

vo u> (

N

^

o ro

ro ro

O O

ro ro

o o

ro ro

o o

in m

H

in

i«0 in

o in

in m

CM

O

ro

H

ro CO

m CO

O

o

m ro

(N

O

0\ rsj

in m

m

m H

o

fv) ro

o CM

o m

(N (N

H

m

o o

o o

m o

fvj ro

80

u 0

o V 10

to

H

0

u H

m d

+ H

u o

+

M-l 0

CQ 0)

•H 4J •H n 0 u

• H >

•H 4J Id H 0

1 H 1 0

!§ 1 j j 1 V 1 O 1 1 1 H

1 H 1 0

; s 1 4J

1 a 1 0) 1 » 1 1 1 H

1 H 1 0

; § 1 X 1 <D 1 K 1 1 1 H

1 H 1 0

l § 1 JJ 1 C 1 (U 1 04 1 1 1 H

1 H 1 0

!§ 1 j j 1 3 1 PQ 1 1 1 H

1 H 1 0

l § 1 a 1 0 t U 1 04 1 1 1 H

^ i t 1

C 1 U 1 C - . 1 0 2 1 U - " 1

Ji ' c- 1

• 1

C 1 U 1 a— 1 O S 1 U ^ 1

1 U 1

1 cr 1 1 * 1 1 C 1 1 U 1 1 C ^ 1 1 O S 1 1 U - - 1

1 U 1 1 C 1

1 • 1 1 a 1 1 0 1 1 G'-. 1 1 O S 1 1 U " ^ 1

\^ i C 1 u C ^ 1

OS ' U ^ 1

U 1 C * 1

• 1

C 1 U 1 C-^ 1 O S 1 U ^ 1

fS

O O

O O

in

H

V0

o in

H CO

in vo

o H

o V0 00 00 o

tN n

o ro m o

H

O O

^ ^

H

fS ^

00

H

00

H

CN

VO

o

n

o m

H 00

o o

H

N

(N eg

o o m

o

H

m

o o

m m

vo

00 o m m H

o i n p » o o c n H f N n O O O O O H H H

o o o o o o o o o

H o t O n 0> vo CN (N (N < in H 00 H • a

vo (N H H H f M ^ O O m H

o n l n o ^ o f N l n t > O O O O H H H H

o o o o o o o o

00 vo p* r * f < ) H f f i p - p > - o o c o r>j ^ ^ 00 in

• • • • • ro vo 00 H H C N n o O C N C N C N

o o

vo o

r«j H

in H

O CN

in (N

P~ (N

O n

o o

M n

81

91

I 0)

H

u e in N V

cd

n

I

+

n 0)

•H ^ • H CO o u n

•H

>

> •rl 4J lO

H 0)

1 a; 1 I C I

! 1 1 m 1 H 1 > i 1 4J 1 U 1 O 1 1 1 C

1 (U 1 a

1 n 1 H 1 >M 1 j j 1 ft 1 dj 1 a 1 1 1 e

> <D 1 CI

1 m 1 i H

i ^ 1 QJ

1 ffi 1 1

1 a

1 0 1 C

i l 1 H 1 > , 1 JJ 1 S 1 n 1 1 1 C

t i • 1

d 1 U 1 C — 1 O S 1 U — 1

=^

C 1 U 1 a — 1 0 2 1 U > - 1

^ ^

! ci 1 1 U 1 1 C - . 1 1 O Z 1 1 U ^ 1

^ • 1

C 1 U 1 C-^ 1 O S 1 U ^ 1

o o

in

o o

o

(N

o

o

00

fN ^

in

CO

H

o

o 00

o fN] CN

O

o o in

o H

o o (N

n n

•H

S S

in

o

m <o H

o o o

in U5

H

o o

o

H o (N

O r j

o

n r-H

O CN

O

V£ in

CN

O n o

U5 o CN

o in

o

r* fN]

P~

o ^ o

< m ^

o o

o

00 Oi

1

n H

o m o

a\ o m

o m

o

-0 •H X) u s in in

o

r* CO

m

m >

o

-d

X)

O o

CNj r o

82

0

o H

• N

1

0) H JD

(3 H

ei 0)

• H 4J • p | CQ 0 u CQ

• H

> 0) >

•H

^ (d H V Pi

1 QJ 1

1 d 1

1 E 1 ffl 1 H 1 >^ 1 JJ 1 U 1 O 1 1 1 C

1 0)

1 a i-g 1 fO 1 H 1 > , 1 i J 1 CU 1 CU 1 a 1 1 1 C

1 (D 1 C

1 "c 1 rt 1 H

ir 1 K 1 1 1 C

1 OJ 1 C

!-g 1 rt 1 H 1 > i 1 XJ 1 3 1 PQ 1 1

1 a

U 1 C^ 1

1

C 1 U 1 C — 1 O S 1 U — 1

^ ' cr* 1

* 1 C 1 U 1 C — 1 O S 1 U — 1

1 U 1 C* 1

1 U 1 1 C - > 1 1 O S 1 1 U — 1

I U 1 C ' 1

• 1 C 1 U 1 C - - 1 O S 1 U ^ 1

ro VC

H

O O

(N <ri

H

O H

VC

ts

fS

o <N

fN O

in

Ln CN

V0

ro (N H

O ro

T}*

^ m H

n n

n

o o

o o

o o

00

o

O

U) Oi

o in

n in m

o n

o

(N

O m

o o

o o m

o

o o o

m

in ro

(N vc en

o in

ro 1.0

<o ^

o o

r ro

(N C

co 00

o in

o fN fN tN

O O

m

fS

83

H H •

cs I U H

0

n 0) •H iU •H n 0 u n •rl >

•H

Id H 0)

1 Q) 1

1 fl 1

11 1 5 1 H 1 > i 1 JJ 1 U 1 O 1 1 1 C

1 dJ 1 G

\t 1 nJ 1 H 1 > i 1 4J

1 a 1 0 1 a 1 1 1 13

1 o; 1 C

11 1 H

i ^ 1 S 1 1

1 a

1 (U 1 a

n 1 H 1 > . 1 JJ 1 3 1 PQ 1 1 1 G

H ' ^ 1

• 1

ti 1 U 1 C — 1 O S t U - - 1

^ * 1

C 1 U 1 C ^ 1 O S 1 U ^ 1

^

I ci 1 1 V 1 1 C — 1 1 O S 1

V ^ 1

^ • 1

d I 0 1 C - . 1 O S 1 U ^ 1

o t

H

o o

in CO

1

H

o H

H H

f

(N

o rN

(N

ro 'J*

LD M

P~

* CO

O ro

VC CT\

O H

n ro

o

H

o o o

o

H

o o o

o

H

o o

H 00

H

o

o

H

O

o

CM

H

LD

o

H

(N

o n o

in

H

O

m o

CO

H

o o

^ f*

m

o

^

o o H

0^ 0 \

H

o in

CO H

CO

o in

o

m

^

o m H

o fN

O o

00

Tf

in

(N

CN

84

0

N

• <N

1 0)

H

1 tH

n 0)

•H •u •H n 0 u to

•H > Q) >

•H a <d H 01 «

1 <U 1 a

1 rt 1 H 1 > . 1 j j 1 U 1 O 1 1 1 a

1 0) 1 C

i-g 1 fO 1 H 1 > i 1 JJ 1 ( ^ 1 0) 1 a 1 1 1 C

1 0) 1 fl

:i 1 rt 1 H

i ^ 1 S

\ C

1 0} 1 a

:i 1 (fl 1 H 1 > i 1 JJ 1 3 1 a 1 1

1 a

^ • 1

G 1 U 1 fl-s 1 O S 1 U - ^ 1

^ 1 1

C 1 U 1 C ^ 1 0 2 1 V^ 1

J ' Cf 1

c 1 U 1 C^ 1 0 2 1 U — 1

U 1 G^ 1

• 1

C 1 V 1 a — 1 0 2 1 U - - 1

in

H

O O

vc > H

o H

H O

<N

O

n

ID

i£

o

1/1 in

CO

in

o o

^ O H O

I I

(N in

o O

in n

o in

in

H

o o o

m H

o o

H

H

O

O

O

H

o m

00

H

o in

o

H

O o

H O

^

o o H

n

H

o m

H

^

o in H

o CN

o o

CN

Tf

in

rs

CN

85

H t

I 01

9

d

H U

o

+

u a

O

01 Q)

• H 4J •H (Q 0 U tfl •H >

0) >

•H 4J 10 H 01 (4

1 QJ 1 C!

i 1 1 r-! 1 > i 1 JJ 1 0 1 O 1 1

1 fl

1 (U 1 d

1 ttj 1 H 1 > i 1 4J

1 a 1 CD 1 W 1 1

1 a

1 Q) 1 d

i 1 1 H

ir 1 a 1 1

' d

1 0) 1 d

i l 1 H 1 > . 1 -U 1 3 1 PQ 1 1 1 d

^ • 1

d 1 U 1 d ^ 1 O S 1 U ^ 1

^ • 1

d 1 U 1 d - - 1 O S 1 U — 1

^

d 1 1 U 1 1 d - - 1 1 O S 1

U - ' 1

> 1 • 1

d 1 O 1 d ^ 1 O S 1 U ^ 1

o ^

• H

o o o

o ^

• H

o o o

o T**

H

o o o

o 'd*

CN CO

1

m

o H

O

o CN

• n

o (N

O

CO

r* H

CO <N

O

o CO

^ vo

1

o H

tn H

o

> c H H

o n o

o n n

o in o

o> CM

^ \o

• ^ ^

CO H

o

r-p-

o CM

O

^ o

o H

in

o o H

o o

o vo

• o r*

o (N

O

> U)

o <N

Wl rf

O

P* M

If)

O P*

H

00

o

^ H

• CO

m H

m (N

O

m r» o (N

CO T}<

o

p-CO

tf)

IT) P*

OJ

o f -

1

CN

ro vo

O

n o

M

^ P» H

O If)

o -0 •H A l-i

o o M

-0 • H

A M ^

If) n o

•0 • H

X3 l-i e tn tn o

fN (N

O O o

tn

o o o o

o (N

86

H U

c

1 H

U

o

^ ro

1

H

O O

H C

• (N

O H

in r

• c

1/1 H

r-0^

• vo (N

00 H

o in

• fs ^

o (N

ro CN

• in O H

ID (N

> O

• LO « (N

O M

u u

4-1

0

0)

H

a 0) K

I

Tt* ro

• H

O o

U) CO

• fN

o CN

(N o

• CTi

O ro

^ ro

• r» H

O ^

ro CO

• P* H

in 'i*

a\ CO

• UJ H

00 «*

Vfi l£

• VD H

O ID

H

0) H

V4

n 0)

•H •u •H (0 O u n

•H

>

> •H 4J (0 H 0) (Hi

0)

(T3

a; I

H >, 4J

3 m

I

c

a u

c u

ro

o o

ro

o o

^ >

CO (N

U3 CO

o in

CN

ro

o in

H

O O

o o

CN

o m

o CN 1/1 m

o

o o

O o CN

in

CN

87

u

u u

0

m H •

N 1

9) H

•3 H

0) •rl •U

0 y n •H

>

0) > •H 4J (« H 0) Cti

u e

10

n 0) d

1 1 d

u o I

H

(0

H

I

c

ci*

d u OS

u OS

d u

5S

^

n H

O O

o

n n H

O

o o

ro

H

o o o

H

o o o

o H

O

in

O

O

n

H

00

o

CO

H

O in

o

o

in H

O

in (N

t

CO

o

o

in

n

o in

o

CO

H

o o H

00 H

00 H

o

00 H

in H

o

o

CO

TJ*

o o H

o

H

o m H

o

CO

O

o

o

H

m

o

0

^

o

H

00

H

o o (N

m

O

in

in

H

CO

o

V0

in

CN

H 1 fS 1

in 1 CN 1 H 1

O 1 ro 1

O 1

p» 1 O 1

in 1 H 1

O 1 m 1

O 1

88

vo

H

I

« H

t

H U

a o +

0

tfl 0)

•r l 4J • H d]

0 u n •H > >

•H 4J (0 H V Oi

u 0 O

10

n 0) a

1 0 1 1 C

1 (0 1 H 1 1 > i 1 1 JJ 1 1 U 1 1 O 1 1 1 1

1 c

1 0) 1 a

1 (0 1 H 1 > , 1 JJ 1 04 1 CU

1 a 1 1 1 C

1 Q; 1 C

i 1 1 H

i ^ 1 a 1 1 1 G

1 (U 1 a

i 1 1 H ' > i 1 ^ ' 3 1 CQ 1 1 1 d

^ • 1

C 1 U 1 C — 1 O S 1 U ^ 1

^ • 1

CI 1 U 1 C-^ 1 0 2 1 U - - i

^

U i 1 C ^ 1 1 O S 1

O ^ 1

\ ^ 1 • 1 1 a 1 1 U 1 1 C - « 1 1 O S 1 1 U ^ 1

(N

H

O O

o

H

O O

O

(N

H

o o o

CN

H

O O

o

in H

O H

O

O

CN

O CN

o

H

CO CN

O

n CO

H

O in

o

in

m H

o

o

o

O

O

M

O in o

CO CO

H

o o H

m CO

n H

CO H

o

n

n H

o

o

Tf

o o H

CO

H

o in

H

CO

CO H

O CN

O

H

m

o

00

^

o

H

10

H

O

o fN

m

o

CO in

H

CO

o

CN

n m

m

CN

O 1 H 1

vo 1

O 1 ro 1

O 1

vo 1

* 1

H 1

O 1 in 1

O 1

81)

rsi

O

•o 0)

LO E C)

o ^ ^

r. ,, c

CO

o

o u

o

o .

E ^

^ ° o

CM

O IT o

o u

01

o CJ

o o

c

o

CO

o

O

<r 6

c _o

D L-

C

u c o u

cr^p

^ to

O

<_) (/) >

>

•J • o

O

o

c o

• • - '

o

O

o

c

• o

a

-o

QJ O) ci;

cr o —

CM

cn

h

GO

o ^

o OsJ

C O

• i - J

3 — J

O

, o M

UD

O

+

CSJ

t—

00

O

<r

o

o

-—~ S

01

o

o (.J

<

'•— o

c o

'*-o

-*-J

c w u c: o u

o a- o " o

2; CM

CD

••— O

l/l OJ

^^ l/l o u i/i

> O)

> •v-»

a OJ

v^_ o

1/1 E r:

o en o _ J

CM

CM

i n C\J

a

I/) — •

o r: o u — f

a

c

• o 0) •o •o o

v * ^

o

<j) c o

o c 3

**" o

I/) o

91

ID O

)

o 1

1

k 1

1 ^

<J-

1 —

1

1

f

o

CO

CM

v j

CNJ

O (Nl

CD

t—

Csl

«—

0 0

6

6

o

IE

if)

c 'E <

H -

o c o

• J

o l_

c Ci)

u c o CJ

t _

o d)

o 'e o a. o 5: OJ

o

o ^^\

^^

0)

4-»

t/)

o o

>

> 4-»

o • • ™ '

Q)

o OJ

LL

H-J

a

u) 0)

c 'E o c

•o 0)

•o D

<»— o c o

•f->

o c 3

o

o

en c o •^ 3 „

o ••-» 1

>>

1

C

• o • o o

<*-o (/)

en c

1

c a o

r: » -

• o

— o O »/)

i n C\J

CD

o

o *-•

o Irt

o X3

•« -»

O o •5 c

0)

o

E a

u o 1

c

^L

92

c-c

0

'8

-ir - A C R

0 0-5 1-0 1-5 2-0 2-5

Concentration of Amines ( M )

3-0

Fig. 2-4; Logarithms of relative viscosities of 0-2M

CPC + 0-1M KCi solutions as a function of e

added n-amines at 25 C •

93

affect micellar structure appreciably and hence no

substcuitial change occurs in the viscosity of 0.2M CPC

with or without added O.IM KCl. The shape of the CPC

micelle remains almost unchanged.

There are at least two opposing factors responsib­

le for the micellar growth process. One is the electro­

static repulsion term originating from intermicellar

and intramicellar coulombic interactions which favours

micelles with a high surface area per head group, i.e.,

spherical micelles. Other is due to the hydrophobic

interactions between the hydrocarbon part of the

micelles/monomers which tries to achieve aggregates

with tightly packed chains, i.e., rods or disks.

Mukerjee^ had proposed that an additive which is

surface active to a hydrocarbon-water interface will be

mainly solubilized at the micellar surface and will

promote micellar growth.

The higher chain-length additives {e.g., CsOH,

C7OH or C8NH2) have a strong chance to get embedded

between monomers comprising a micelle. This penetration

of a surfactant - rich film by these additives helps to

overcome head group repulsion by holding these

molecules in between head groups of similar charge and

is, therefore, responsible for the decrease in surface

94

area occupied per surfactant head group (Ag) .

Consequently, the Mitchell - Ninham parameter

Rp(=Vc/lcAo)^^ increase. An increase in this parameter

could be understood by considering the CPC - higher

chain-length additive couple as a single surfactant.

The penetration of the additive will result in

increasing the volume of the micellar core, which is

equivalent to increasing the V - . This seems to result

in an increase of the Rp value. Thus, CPC-higher chain-

length additives should have a tendency to form large

micelles, and it seems to do so as reflected by the

viscosity rise on the addition of higher alcohols and

amines to 0.2M CPC micellar solutions (Tables 2.1-

2.16). Further, the increase in Rp would be greater

with CsOH or C8NH2 than with C5OH or C6NH2. This is due

to the larger hydrophobic volume of Cs which would

increase Rp more with a concomitant formation of larger

micelles and imparting a higher viscosity to the

solution. The viscosity plots (Figs. 2.1-2.4) are

consonant with the explanation. Hartel and Hoffmann^^

used such arguments to design lyotropic nematics. It is

worth recalling that both the anionic SDS and cationic

CTAB micellar solutions with or without added

electrolyte show similar behaviour with CgOH

95

concentration in the whole range investigated^'37-39

It is interesting to note that the presence of

both O.IM KCl and additives (above a certain chain-

length; alcohols: C5-C8OH, amines: Cg-C8NH2) in iarts

very high viscosity to 0.2M CPC micellar solutions in

conparison to the situation where O.IM KCl or various

additives were present singly. This is not the end of

the story-another point of interest is that, in the

presence of O.IM KCl, the viscosity of the 0.2M CPC

micellar solution increases with the increase in

additive concentration (similar to the case without

KCl) , reaches a maximum and then decreases (this

behaviour was obtained with C5OH, CgOH and C7NH2 only).

In all probability, the other alcohols and amines, viz.

C7OH, CBOH and C8NH2, would show the same phenomenon at

higher additive concentrations but studies were

hanpered as turbidity appeared at concentrations beyond

that shown in Tables 2.5-2.8 and 2.13-2.16,

respectively. These two effects show that a special

phenomenon exists when O.IM KCl and additives are

present in the same system. The manifold increase in

viscosity is the result of variation of different

forces favourable for micellar growth. Addition of KCl

to the CPC solution we Jcens the coulombic repulsion

96

between the micelles and intercalation of higher chain-

length additives decreases intramicellar coulombic

repulsive forces and increases hydrophobic forces among

the monomers of the CPC micelle. As mentioned earlier,

the decrease of coulombic repulsion and/or increase in

hydrophobic interactions are favourable conditions for

micellar growth (either one of which exists if O.IM KCl

or organic additive is present singly). The evidence of

growth process due to the combined effect is provided

in Fig. 2.5 where In i|j- vs. concentration of the

additives with the heptyl chain is shown for 0.2M CPC

with and without O.IM KCl.

The observed viscosity decrease at higher

concentrations with the aforementioned additives is

possibly due to the fact that they may be salted-out by

the added 0. IM KCl and start dissolving in the micellar

core rather than remaining in the vicinity of

interfacial region; therefore the requirement of the

surfactant chains to reach the centre of the micelle

becomes relaxed^^. It is, thus, possible that at high

additive contents the larger micelles disintegrate to

smaller ones and form the basis of the viscosity

decrease (Figs. 2.2 & 2.4). The solubility and packing

constraints do not allow C7OH, CgOH or C8NH2 to do so

97

7-0 r

C7NH2

0 0-1 0-2 0-3 0-4 0-5 0-6

Concentration of Additive (M)

Fig. 2-5: Viscosity variation of 0-2M CPC micellar solutions in presence ( « , • ) and absence ( 0 , 0 ) of 0-1M KCi with equal chain-length of additives ( C7OH and C7NH2) at 25°C .

98

as there is not sufficient amount of these additives

available to form the core of the micelle (solubilized

system).

Fig. 2.5 also shows that for equal chain-lengths

(e.g., C7OH and C7NH2) the viscosity rise is more with

alcohols than with amines. It was reported earlier that

C4 to Cio n-alkyl amines are solubilized in SDS eind

CTAB micelles by electrostatic and hydrophobic effects

with the amine group left on the surface of the

micelle^^. Their partial dissociation into -NH3"*" and

OH" (though feebly) may affect electrostatic

interactions with cationic pyridinium head group, which

will hinder the micellar growth. Therefore, for equal

chain-lengths and concentrations of alcohols and

amines, alcohols will be more effective for cationic

micellar growth. This indeed is observed in the present

viscosity results (Fig. 2.5, Tables 2.1 & 2.6).

The effect of ten^erature on the viscosity values

showed an Arrhenian behaviour.' The observed linearity

of the plots shown in fig. 2.6-2.9 is interpreted in

terms of the relational.

In i/ro = In A +£iG*/RT (1)

where A is a constant and AG* is the activation free

energy for viscous flow. As densities of the solutions

2 - 8

99

2-4

2-0 -

1-6 -

1-2

0-8

(0 -1724M )

( 0 -15M )

( 0 - 1 0 M ) ( 0 -05M )

0-4 X 3-15

Fig.2-6

3-20 3-30

1 /T X 10 ( K )

3-40

V a r i a t i o n of In q^^ w i th l / T for

0-2M CPC so lu t ions in presence of

var ious concentrat ions of n -hep tano l

ment ioned in ( ) .

100

7 -

2 -

1 -

0

.( 0-17M)

( 0-15M)

( 0-12M )

( 0-10M)

( 0-09M )

( 0-05M) ^ ( 0 - 0 3 M )

=*>^( 0-OOM) I

3-1 3-2 3-3

1/T X 1 0 ^ ( K " S

3-t*

Fi'g 2-7 .-Variation of In r ^ wfth l / T for 0-2M

CPC-h O l M K C i solutions in the presence

of various concentrations of n-heptanol mentioned in ( ) .

3-5 h

101

3-0

2-5

2-0 h

1-5

(0-577M ) (0-5M)

( 0 - i fM)

3-15

( 0-3M )

( 0-2M)

3-20 3-25 3-30 3-35

/ 3 -1 l / T X 10 ( K )

3-i#0

Ffg. 2-8 Variati'on of In f| j. with l /T for 0-2M CPC solutions in the presence of various concentrations of n-fieptyl amfne mentioned in ( ) •

3-i*

102

3-0

2-6

(0-U5) ( O-i+O)

( 0-50)

(0-30)

2-2 -

1-8

1-^ -

1-0

(0-20)

31

Fig. 2-9

3-2 3-3

I / T ( 1 0 " ^ K " \

3-1*

Variation of In n . with 1 / T for 0-2M

CPC+ 0-1M KCl solutions in tfie presence

of various concentrations of n - f i e p t y l -

amine mentioned in ( ) .

103

were close to the density of water, kinematic

corrections were neglected, cuid values of C^G* were

calculated from the slopes of these straight lines. As

stated earlier, r|j- values were obtained only at four

temperatures in the range of 25°C to 40°C. The lack of

more experimental data points does not preclude in

obtaining good correlation coefficients(r). Estimation

of AG* is, therefore, sufficiently adequate. The r and

calculated ^ G* values are given in Tables 2.17 & 2.18.

It has been shown^ that A G* could be linked to

difference in curvature elasticity of the spherical

end-caps and the cylindrical part of the micelles. A

higher value of A G* implies that very high energy is

required to convert cylindrical micelle to small

micelles which indicates that the life-time of

cylindrical micelles is increased with an increase of

additive concentration. For equal chain-length alcohols

and amines, higher AG* (Figs. 2.10-2.13) has been found

with the former which shows that long cylindrical

micelles with higher life-times are formed with added

alcohols. This confirms our earlier proposition that

micellar growth is slightly hindered by the presence of

amine molecules. Thus AG* values could be used as a

measure of the life-time in micellar structures42,43

104

TABLE-2.17

Values of Activation Free Energies, LG* , for the

Viscous Flow of 0.2M CPC Solutions with (Sp) and

without (Sg) O.m KCl in Presence of Added n-Alcohols

and Correlation Coefficients(r) for the Linear Variation

of In r\/no with 1/T

Alcohol Sa Sp Concn. (M) ^G* r l^G* r

(kJ mol-1) (kJ mol-1)

0.00 2.05 0.9859 4.94 0.9681

1-Propanol 0.50 1.25 0.9880 0.90 0.7808 1.00 -- -- 1-80 0.9405 1.50 2.65 0.9673 2.00 6.16 0.9672 4.98 0.9489 3.05 -- -- 6.94 0.8934 4.00 8.00 0.9880

1-Butanol

0.42 -- -- 13.84 0.9993 0.50 2.07 0.9414 0.83 -- -- 1.24 0.9928 1.00 1.93 0.9803 1.50 1.24 0.9910 1.66 -- -- 5.44 0.9597 2.50 4.03 0.9805 2.99 0.8584

1-Pentanol

0.10 2.68 0.9602 0-14 -- -- 3 21 0.9070 0-30 1.39 0.9963 31.00 0.9909 °- 2 -- -- 25.31 0.9969 0.50 3.87 0.9876 °-^^ -- -- 13.54 0.9964 0.70

105 0.76 1.00 1.52

1-Hexanol

0.06 0.10 0.12 0.15 0.20 0.25 0.27 0.30

7.84 9.33 7.59

1.49 --

4.81 9.95 9.93 --

30.39

0.9907 0.9891 0.9901

_ —

0.9880 --

0.9677 0.9624 0.9519 --

0.9945

11.07 12.72 7.73

3.53 --

36.11 66.44 143.96 65.77 69.77 44.29

0.9626 0.9877 0.9882

0.9476 —

0.9943 0.9982 0.9993 0.9973 0.9977 0.9896

1-Heptanol

0.03 0.05 0.09 0.10 0.12 0.15 0.17

1-Octanol

0.05 0.07 0.08 0.09 0.11 0.12 0.13

--

2.67 --

6.39 --

32.28 59.07

2.50 2.44 --

15.58 --

--

—

--

0.9593 --

0.9912 --

0.9940 0.9959

0.9949 0.9814 --

0.9938 --

--

—

5.19 10.38 32.41 72.93 109.16 129.65 106.03

6.64 33.90 68.74 106.56 127.78 110.74 —

0.9989 0.8818 0.9973 0.9924 0.9972 0.9994 --

0.9774 0.9903 0.9956 0.9975 0.9916 0.9985 0.9923

106

TABLE-2.18

Values of Activation Free Energies, AG*, for the Viscous Flow of

0.2M CPC Solutions with (Sp) and without (S^) O.Uf KCl in Presence

of Added n-Amines and Correlation Coefficients (r) for the Linear

Variation of In ij/i o "itJ* 1/T

Amine S^ Sp Concn. (M) l\G* r AG* r

(kJ mol-1) (kJ mol-l)

0.01 2.05 0.9859 4.94 0.9681

n-Butylamine

0.50 1.00 1.50 2.00

n - Hexy lamine

0.20 0.28 0.50 1.00 1.50 1.70 2.75

n-Heptylamine

0. 0 0, 0. 0.

20 30 40 45 48

0.50

n-Octylamine

0.10 0.15 0.18 0.20 0.25 0.30 0.33

2.66 2.42 3.94 2.33

0.9890 0.9951 0.8412 0.987

1.66 3.45 2.96 2.56

0.9890 0.9126 0.9159 0.9384

3.603 - -4.347 6.685 7.987 - -7.775

5.890 9.38 19.38 — — 31.978

7.25 — — 7.66 34.91 47.63 34.66

0.9773 - -0.9646 0.9985 0.9830 - -0.9784

0.9379 0.9447 0.9873 — - -0.9985

0.9521 — — 0.9204 0.8857 0.9918 0.9955

- -2.59 1.47 4.03 - -13.59 33.22

15.25 26.58 21.31 17.99 13.29 9.49

21.78 43.44 61.19 68.39 59.80 119.17 —

- -0.9618 0.9829 0.9925 - -0.9435 0.9980

0.9866 0.9998 0.9989 0.9956 0.9960 0.9734

0.9888 0.9989 0.9937 0.9987 0.9999 0.9981 _ —

107

O E

to <

• CgOH

Q C7OH

A CgOH

• C5OH

• Cf OH

0 C3OH

t^n-Qlcohol 3 ( M )

2-0 3-0

Fig. 2-10 Variation of act ivat ion free energy (AG ) for the VISCOUS flow of 0-2M CPC solutions as a function of added alcohols.

160 U

108

160

120

' 100 o

-3

80 h

60 ^

A C3OH

Q C7OH

A CgOH

• C5OH

• Ci^OH

0 C3OH

0-8 1-0 1-2

Cn-alcohol 3(M)

Fig. 2-11: Variation of activation tree energy (AG ) for the viscous flow of 0-2M CPC+ 0-1M KCi solutions as a function of added alcohols.

2-0 3-C

109

o E

<3

A

D

A

C3NH2

C7NH2

C6NH2

C4NH2

0

F i g . 2-12

OA 0-8 1-2 1-6 2-0

C n - amine D ( M )

2-4 2-8

V a r i a t i o n of ac t i va t ion f ree energy ( A G ) f o r t he VISCOUS f low of 0-2 M CPC s o l u t i o n s as a f u n c t i o n of added a m i n e s .

110

A

• A

•

CgNHg

C7NH2

CgNHg

Cf,NH2

E

<

120 \-

100 U

- 80 U

0-5 1-0 2-5 30

Fig. 2-13

1-5 2-0

C n - amine ^ ( M )

Varfati'on of activation free energy (AG ) for the vi'scous flow of 0-2M CPC* 0-lM KCi soluti'ons as a function of added amines-

I l l

with the above discussion it can be concluded that

in micellar growth the presence of a salt cind an

organic additive in the system produce favouraUtjle

conditions which do not exist in presence of either the

salt or the additive alone. The electrostatic effect

produced by additives at the micellar surface is a

governing factor in addition to the hydrophobic part of

the additives. In case of additives of equal chain-

length, its efficacy of decreasing AQ decides the

potential of the additive for structural growth. Here

it has been shown as how organic molecules can be used

for viscosity enhancement which is desirable for

various industrial applications/reaction media where

lower ionic-strength is required.

112

REFERENCES

1. P.J. Missel, N.A. Mazer, M.C. Carey and G.B.

Benedek, in "Solution Behaviour of Surfactants",

Edited by K.L. Mittal and E.J. Fendler, Plenum

Press, New York, Vol.2, p.373, 1982.

2. S.J. Candau, E. Hirsch, R. Zana and M. Delsanti,

Langmuir, 5, 1225 (1989) and references therein.

3. G. Porte and J. Appell, J. Europhys. Lett., 12,

190 (1990).

4. S. Kumar, Kirti, K. Kumari and Kabir-ud-Din, J.

Am. Oil Chemists Soc, 72, 817 (1995).

5. S. Kumar, Kirti and Kabir-ud-Din, J. Am., Oil

Chemists Soc, 71, 763 (1994); Ch. D. Prasad and

H.N. Singh, Colloids surf., 59, 27 (1991).

6. S. Kumar, V.K. Aswal, H.N. Singh, P.S. Goyal and

Kabir-ud-Din, Langmuir, 10, 4069 (1994) .

7. S. Kumar, S.L. David and Kabir-ud-Din, Langmuir,

(1995) (communicated).

8. P. Mukerjee, in "Solution Chemistry of

Surfactants", Edited by K.L. Mittal, Plenum, New

York, Vol.1, 1979.

9. E.B. Abuin, E. Valenzuela and E.A. Lissi, J.

Colloid Interface Sci., 101, 401 (1984).

Y. Moroi and R. Matuura, J. Colloid Interface

Sci., 125, 463 (1988).

10

113

11. B. Hwan Lee, S.D. Christian, B.E. Tucker cuid J.F.

Scamehom, Langrauir, 6, 230 (1990) .

12. F. Gadelle, W.J. Koros and R.S. Schechter, J.

Colloid Interface Sci., 170, 57 (1995).

13. Ch.D. Prasad, H.N. Singh, P.S. Goyal and K.S. Rao,

J. Colloid Interface Sci., 155, 415 (1993).

14. P.M. Lindetnuth and G.L. Bert rand, J. Phys. Chem.,

97, 7769 (1993) .

15. M. Monduzzi, U. Olsson and O. Soderman, Langmuir,

9, 2914 (1993) .

16. F. Grieser emd C.J. Drummond, J. Phys. Chem., 92,

5580 (1988) .

17. S.J. Rehfeld, J. Phys. Chem., 75, 3905 (1971).

18. P. Mukerjee and J.R. Cardinal, J. Phys. Chem., 82,

1620 (1978) .

19. G.A. Smith, S.D. Christian, E.E. Tucker and J.F.

Scamehom, J. Colloid Interface Sci., 130, 254

(1989) .

20. R. Gomati, J. Appell, P. Bassereau, J. Marignan

and G. Porte, J. Phys. Chem., 91, 6203 (1987).

21. G. Porte, J. Appell and Y. Poggy, J. Phys. Chem.,

84, 3105 (1980) .

22. G. Porte and J. Appell, J. Phys. Chem., 85, 2511

(1981).

114

23. J. Appell and G. Porte, J. Colloid Interface Sci.,

87, 492 (1982) .

24. J. Appell and G. Porte, J. Colloid Interface Sci.,

81, 85 (1981).

25. G. Porte and J. Appell, in "Surfactants in

Solution", Edited by K.L. Mittal and B. Lindman,

Plenum Press, New York, p.l, 1984.

26. J. Appell and J. Marigpaen, J. Phys. II France, 1,

1447 (1991).

27. M.B. Smith and A.E. Alexander, Proc. Ilnd

International Cong. Surface Activity, Butter-

worths, London, Vol.1, 1957.

28. M. Malaiyandi, R.H. Wightman and C. La Ferriere,

Adv. Chem. Ser., 214, 163 (1987).

29. S.D. Christian and J.F. Scamehom, in "Surfactant

Based Separation Processes", Bdited by J.F. Scame­

hom and J.H. Harwell, Marcel Dekker, New York,

1989.

30. A. Khatory, F. Lequeux, F. Kern and S.J. Candau,

Langmuir, 9, 1456 (1993).

31. C. Gamboa and L. Sepulveda, J. Colloid Interface

Sci., 113, 566 (1986).

32. S. Ozeki and S. Ikeda, J. Colloid Interface Sci.,

77. 219 (1980) .

P. Mukerjee and K.J. Mysels, in "Critical Micelle 33.

115

Concentrations of Aqueous Surfactant Systems",

NSRDS-BS 36, Washington D.C., 1971.

34. D. Mitchell and B.W. Ninham., J. Chem. Soc,

Faraday Trans.2, 77, 601 (1981).

35. Z. Lin, J.J. Cai, L.D. Scriven and H.T. Davis, J.

Phys. Chem., 98, 5984 (1994).

36. G. Hartel and H. Hoffmann, Liq. Cryst., 5, 1983

(1989) .

37. Ch. D. Prasad and H.N. Singh, Colloids Surf., 50,

37 (1990).

38. S. Backlund, J. Bakken, A.M. Blokhus, H. Hoeiland

and I. Vikholm, Acta Chem. Scand. Ser. A,40, 241

(1986) .

39. T. Tominaga, T.B. Stem and D.F. Evans, Bull. Chem.

Soc. Jpn; 53, 795 (1980).

40. T. Yamashita, H. Yano, S. Harada and T. Yasunaga,

J. Phys. Chem., 87, 5482 (1983).

41. L. Sepulveda and C. Gamboa, J. Colloid Interface

Sci. , 118. 87 (1987) .

42. F. Kern, R. Zana and S.J. Candau, Langmuir, 7,

1344 (1991) .

43. R. Makhloufi, E. Hirsch, S.J. Candau, W. Binana-

Limbela and R. Zana, J. Phys. Chem., 93, 8095

(1989) .

CHAPTER - III

EFFECT OF ALIPHATIC AMINES AND TEMPERATURE ON

THE STRUCTURAL TRANSITION OF CETYLTRIMETHYL-

AMMONIUM BROMIDE MICELLES IN AQUEOUS

POTASSIUM BROMIDE SOLUTION

117

In the studies of micellar growth processes in

solutions, the most extensively studied systems are

alkyltrimethylammonium and alkylpyridinium halides^"^.

The surfactant used here to form the basic micellar

structure is cetyltrimethylaramonium bromide (CTAB).

CTAB has a cmc of 0.99mM at 25°c5. A body of

interesting information on micellization of CTAB and

related compounds in water-alkanol mixtures can be

found in a series of papers published by Zana and

coworkers 6-11.

At O.IM concentration, CTAB forms ellipsoidal

micelles^ which may further grow to long rods at higher

concentrations. The presence of rod-shaped micelles

gives a high viscosity to the solution. In many

instances an abrupt increase in the viscosity of

micellar solutions in presence of additives has been

interpreted in terms of micellar sphere-to-rod

transitions. High viscosities observed for CTAB

solutions in the presence of salts^^ or hexanol^^ have

been explained in light of micellar growth which occurs

over a certain range of concentration of either

surfactant or additive. Such transitions from rod-to-

sphere by the addition of lower alcohols to CTAB (or

its lower homologs) in aqueous solution and micellar

growth in presence of higher alcohols have been

113

reported ^^' ^^. They have explained the viscosity rise

in terms of incorporation of the alkanols inside the

micelle but the explanation invoked for the observed

viscosity decrease in presence of medium chain alkanols

(butanol or pentanol) at higher concentrations seems

unlikely. At higher concentrations, it is possible that

these medium chain alkanols may be salted-out by the

added NaBr and dissolve preferentially in the micelle

hydrophobic core rather than in the palisade layer;

thereby the requirement of the surfactaint chains to

reach the centre of the micelle becomes relaxed • ;

thus viscosity decrease takes place.

The effect of the addition of alcohols and amines

on viscosity behaviour of CPC in presence or absence of

salt (KCl) is already reported in Cliapter II. Since

structure of CTAB is quite different than CPC, as the

latter contains a benzene ring and the counterion is

also different, it was thought worthwhile to extend our

study of organic additives with the CTAB (this

surfactant is the most extensively studied in its o%m

class of compounds) . Further, the salt used here, i.e.

KBr, has itself a role in micellar growth. This was not

the case with CPC/KCl system where KCl only screens out

Coulombic repulsions but has no role towards the

119

micellar growth at the concentration enployed in the

studies. In this chapter the results of studies on CTAB

micellar system with added aliphatic amines in presence

of 0.1 M KBr solutions are presented.

Experimental

CTAB from E. Merck (Darmstadt, Germany, 99%) was

recrystallized twice from acetone. The surfactant was

dried after filtration in a hot air oven at 50°C. The

purity of the surfactant was ascertained from the

absence of minimum in the surface tension vs. logarithm

of concentration plots. KBr (E. Merck) was heated

(~60°C) for one hour and was stored in a desiccator

(containing Pi^B^ • "^^ amines used were the same as

mentioned in Oiapter II. The methods of sample

preparation and viscosity measurements were also the

same as described in Chapter II.

Results

The variation of relative viscosity of O.IM CTAB

solutions with the addition of KBr is shown in Fig.

3.1. The viscosity values of O.IM CTAB + O.IM KBr

solutions obtained by adding different amounts of n-

amines (C4NH2, C6-C8NH2) at four tenqperatures 30, 35,

40 and 45°C are recorded in Tables 3.1-3.4. These

results are depicted graphically in Figs. 3.2-3.5.

120

0.0 0.0 O04 0.08 0.12

[KBr] (M)

0.16 0.20

Fig. 3-1 • Effect of KBr concentration on the relative viscosity

of 0.1 M CTAB micellar solution at 30* C .

121

TABLE 3 . 1

R e l a t i v e V i s c o s i t i e s ( i^) o£ O.Uf CTAB + 0.111 KBr

i n p r e s e n c e o f n-amines a t 30*C

n-Buty lamine n-Hexylamine n-Heptylamine n-Octylamine

Concn. r^ (M)

Concn. i^ (M)

Concn. i^ (M)

Concn. i\^ (M)

0.00 4.77

0.100 1.79

0.150 1.56

0.200 1.31

0.600 1.39

0.700 1.40

0.0 4.77 0.0 4.77 0.0 4.77

0.020 6.69

0.050 8.07

0.100 5.29

0.175 3.65

0.250 3.18

0.350 2.97

0.025 31.60 0.010 11.85

0.060 115.02 0.020 73.52

0.075 117.20 0.030 259.99

0 .100 9 7 . 1 4

0 .125 4 5 . 1 0

0 .040 532 .84

0 . 0 6 0 678 .58

0.130 Turbid 0.075 190.69

0.400 Turbid 0.080 Turbid

122

TABLE 3.2

Relative Viscosities (i ) of O.IM CTAB + O.IM KBr

in presence of n-amines at 35*C

n-Butylamine n-Hexylamine n-Heptylamine n-Octylamine

Concn. r\j-(M)

Concn. i^ (M)

Concn. HJ-(M)

Concn. r\j-(M)

0.0 2.82 0.0 2.82 0.0 2.82 0.0 2.82

0.100 1.43

0.150 1.38

0.200 1.23

0.600 1.36

0.700 1.38

0.020 3.76

0.050 4.29

0.100 3.75

0.175 2.73

0.250 2.79

0.350 2.89

0.025 12.80

0.060 46.09

0.075 48.85

0.100 47.91

0.125 17.36

0.010 5.10

0.020 20.70

0.030 30.86

0.040 131.78

0.060 251.47

0.075 175.86

123

TABLE 3.3

Relative Viscosities {T\^) of O . U M C T A B + O.IM KBr

in presence of n-amines at 40'C

n-Butylamine n - Hexy lamine n-Heptylamine n-Octylamine

Concn. HJ-(M)

Concn. r\ (M)

Concn. r\r (M)

Concn. r\r (M)

0.0 1.94 0.0 1.94 0.0 1.94 0.0 1.94

0.100 1.31 0.020 1.81 0.025 5.91 0.010 2.77

0.150 1.28 0.050 2.67 0.060 16.49 0.020 8.74

0.200 1.22 0.100 2.67 0.075 22.13 0.030 10.33

0.600 1.35 0.175 2.50 0.100 23.84 0.040 35.99

0.700 1.37 0.250 2.54 0.125 11.96 0.060 89.90

0.350 2.72 0.075 135.83

124

TABLE 3.4

Relative Viscosities (i^ ) of O.IM CTAB + O.IK KBr

in presence o£ n-amines at 45"C

n-Butylamine n-Hexylamine n-Heptylamine n-Octylamine

Concn. rj-(M)

Concn. r^ (M)

Concn. HJ-(M)

Concn. n_j-(M)

0.0 1.48

0.100 1.22

0.150 1.20

0.200 1.19

0.600 1.34

0.700 1.35

0.0 1.48 0.0 1.48 0.0 1.48

0.020 1.64

0.050 1.91

0.100 2.04

0.175 2.09

0.250 2.34

0.025 3.33

0.060 7.64

0.075 10.69

0.100 10.99

0.125 7.90

0.010 1.91

0.020 4.26

0.030 4.18

0.040 13.05

0.060 37.82

0.350 2.57 0.075 84.94

125

7.0

6 0

5 . 0 -

4.0

Q -

• -

<8) -

0 -

C4NH2

C6NH2

C7NH2

C8NH2

Fig. 3 - 2 : Logorifhms of relative viscosifies of 0.1 M CTAB -»-0.1M KBr solutions as a function of added n-onnines at 30 °C •

7.0

128

c

6.0

5.0

4.0 -

0 0 O

9 •

0 O

C4NH2

CgNHg

C7NH2

CgNHg

0.1 0.2 0.6 0.7

Rg 3.3

0.3 0.4 0.5

[ n - amines ] (M )

Logarithms of relative viscosities of 0.1 M CTAB + O.IN

solutions as a function of added n-omines at 35*C .

127

7.0

6.0

Fig. 2k

Q •

(S) 0

C4NH2

C6NH2

C7NH2

C8NH2

0.2 0.3 0.4 [ n - amines] 'MJ

0.5 0.6 0.7

Logarithms of relative viscosities of 0.1 M C T A B - J - 0 . 1 M KBr

solution as a function of added n - amines of ^O'C .

128

c

5.0

0.3 0.4 0.5 [ n - amines] (M/

0.6 0.7

Fig. 35 • Logarithms of relative viscosities of 0.1 M CTAB + O.t M Kdr

solutions as a function of added n-amines at ^5 C •

129

1-6 ( D O O M )

c

}'k

1-2 -

1-0

0'8

0-6

0-^

0-2

0-0 3-1

1 3-2

( 0 - 1 0 0 M )

( 0-150 M ) ( 0-70M ) ( 0 - 6 0 0 M )

( 0 -200M)

3-3 3 t f

l / T ( 10"^K'^

Ffg. 3-6: Variation of Inn with I / T for 0-lM

CTAB + 0-lMKBr solutions in presence

of various concentrations of n -buty l -

amine mentioned in ( ) .

130

3-0

2 0

1-0

0-0 3-10 3-20

( 0-050 )

( 0-020M)

( 0 1 0 0 M ) 0-OOOM)

( 0-175 M )

( 0-250M) ( 0-350M)

3-30

, -3 . - 1 3-f+O

I / T ( 1 0 ' ' K )

Fig. 3-7: Variation of In q ^ with l /T for 0-lM

CTAB + 0- lMKBr solutions in the presence

of various concentrations of n-hexylamine

mentioned in ( ) -

131

50

k-0 -

C

2-0

0 0

3-10

Fig.3-Q :

3-20

(0-060M)

(0 075M)

(OlOOM )

(0-125M)

(0-025M)

(0-OOOM)

3-30

-3 -1 1/T(10 K )

3 i f 0

Variat fon of ln ( (^p ) with 1/T for

0-1MCTAB+ 0-IMKBr solutions in the

presence of various concentratfons

of n - heptylomine mentioned in ( ).

132

6-0

k-Q

2-0

0-0

3-10

( 0-060 M)

( 0 - 0 ^ 0 M)

( 0 0 7 5 M)

( 0-030 M)

( 0"020 M)

( 0-010 M )

( 0-000 M )

3-20 3-30 / -3 -1

1 / T ( 1 0 K )

3-/*0

Fig. 3-9 •• Variation of In n^ with 1 / T for 0-1M

CTAB + 0-1M KBr solutions in the presence

of various concentrations of n- octylamine

mentioned in ( ) .

133

Figs. 3.6-3.9 show the variation of In n/i\o v s. 1/T for

different concentrations of C4NH2, C6NH2, C7NH2 and

C3NH2, respectively. These straight line plots were

used to evaluate the activation free energies (illG*) for

the viscous flow.

Discussion

When a salt is added to a surfactant solution and

its concentration reaches a threshold value, non-

spherical micelles form because the presence of salt

ions near the polar heads of the surfactant molecules

decrease the repulsion force between the head groups. A

reduction in the repulsion makes it possible for the

surfactant molecules to approach each other more

closely and form larger aggregates which requires much

more space for the hydrophobic chains. This leads to a

sharp rise in i|/i\o.* ^^ the present system (of 0.1 M

CTAB) it occurs around 0.1 M KBr (Fig 3.1) indicating

the formation of larger aggregates^2-20 (rod-shaped

micelles): this being the reason of choosing O.IM CTAB

+ O.IM KBr system for the detailed study of the effect

of n-alkylamines and ten^jerature.

Data in Tables 3.1-3.4 and Figs. 3.2 - 3.5 show

that the addition of an amine may either decrease or

increase the viscosity of the starting solution (i.e.,

134

0.1 M CTAB + 0.1 M KBr) . It is further seen that the

increase or decrease of viscosity depends upon chain-

length and nature of the added amine. With Cg -, C7 - and

Cs" amines, the viscosity rises abruptly, followed by a

decrease. The effect was progressively more pronounced

for C7- and Cs-amines. In case of C4NH2, viscosity

decreases right from the beginning. This behaviour of

C4NH2 may be due to the hydrophilic nature of the

amine; it is partitioned more in the aqueous phase

which affects the water structure and causes the

breaking of initially present large micelles in the

solution^l. Addition of C4NH2 results in breaking of

initially present rod-shaped micelles to spherical with

a concomitant decrease in the viscosity value

coitparable to globular micellar solution. Such

transitions from rod-to-sphere by the addition of

lower alcohols to dodecyltrimethylammonium bromide/

sodium salicylate micelles have been reported from

light-scattering measurements^^. The viscosity

increment at low concentrations of higher amines (cg

C3) can be interpreted in terms of the formation of

large micelles due to their solubilization/incorporat­

ion into the micelles. Thus viscosity increase could be

understood if we consider CTAB-higher amine as a single

surfactant. This will affect the Mitchell-Ninham

135

parameter of the surfactant. A detailed discussion

regarding this parameter in connection to the

structures formed in solutions is already given in

previous chapters.

The initial increase in viscosity reflects that

longer chain-length amines solubilize preferentially in

micellar palisade layer and lower the surface charge

density, which is responsible for micellar growth.

Further addition of the amine beyond a certain

concentration affects the solubilization site of the

additive in micellar aggregates resulting in the

breaking of giant aggregates to relatively smaller

ones, and hence, a gradual decrease in viscosity is

observed. This decrease could be explained in the light

of micellar core solubilization of amines. This core

solxibilization releases the requirement of surfactant

chain to reach the centre of micelle and micelle gets

shortened in this situation (at higher amine

concentrations) and responds to viscosity decrease.

Estimation of the free energies of activation,

AG*, was done using the plots of In rj- vs. 1/T (Figs.

3.6-3.9), The r and calculated A G * values are given in

Table 3.5. The variation of A G* with concentration of

the added amine is shown in Fig 3.10. It may be seen

136 TABLE 3.5

Activation free energies ( 6*) for the viscous £low o£

O.IM CTAB + 0.1 M XBr solutions in presence o£ n-amines

and correlation coefficients (r) for the linea:-

variation of In i\/i\jo with 1/T.

Concn. of amine (M) AG* (kcal mol-l)

0.00 14.884 0.9981

n-Butylamine

0 . 1 0 0 0 . 1 5 0 0 . 2 0 0 0 . 6 0 0 0 . 7 0 0

4 . 7 7 4 3 . 0 3 8 0 . 8 9 3 0 . 5 2 7 0 . 4 1 3

0.9943 0.9987 0.9873 0.9972 0.9919

n-Hexylamine

0.020 0.050 0.100 0.175 0.250 0.350

n - Hep ty lamine

0 . 0 2 5 0 . 0 6 0 0 . 0 7 5 0 . 1 0 0 0 . 1 2 5

18.985 18.371 12.221 6.752 3.873 1.473

28.561 34.975 30.447 27.715 21.448

0.9995 0.9928 0.9992 0.9892 0.9958 0.9976

0.9949 0.9990 0.9970 0.9991 0.9847

n-Octylamine

0 . 0 1 0 0 . 0 2 0 0 . 0 3 0 0 . 0 4 0 0 . 0 5 0 0 . 0 7 5

23.339 35.927 51.696 47.526 37.040 10.217

0.9980 0.9943 0.9814 0.9985 0.9997 0.9896

137

0.0 0.2 0.4

[ n - amine] ( M )

0.6 0.8

F'\g. 3-10 '• Variarion ^f activation free energy for the viscous flow

of 0.1 M CTAB -+-0.1M KBr solutions as a function of added n-annines.

138

that t^ G* values are highly dependent on the nature and

concentration of the additive. The higher values of Z G*

correspond to the formation of larger aggregates

(elongated rods) and low values to the smaller

aggregates (spherical micelles). The magnitudes of A G*

for different amines indicate that higher chain-length

amines are capable to induce the growth process of

micelles upto a optimum concentration, beyond which

micellar core solubilization (a change of site) comes

into picture. The low values of A G * for C4NH2 show

that the water structure factors play an iir orta it role

with this hydrophilic additive with a concomitant

breaking of larger aggregates.

139

REFERENCES

1. T. Imae and S. Ikeda, J. Phys. Qiem., 90, 5216

(1986) .

2. F. Kern, P. Leinarechal, S.J. Candau and M.E.

Gates, Langrauir, 8, 437 (1992)

3. J. Appell and G. Porte, Europhys. Lett., 12, 185

(1990) .

4. S.J. Candau, E. Hirsch, R. Zana and M. Adam, J.

Colloid Interface Sci., 122. 430 (1988).

5. R. Lawrence and R. Stenson, Proc. 2nd

International Congr. Surface Activity, London,

p.388, 1957.

6. R. Zana, S.Yiv, G. Strazielle and P. Lianos, J.

Colloid. Interface Sci., 80, 208 (1981).

7. S. Candau, E. Hirsch and R. Zana, J. Colloid

Interface Sci., 88, 428 (1982).

8. S. Yiv and R. Zana, J. Colloid Interface Sci., 65,

286 (1978).

9. S. Yiv, R. Zana, W. Ulbricht and H. Hoffmann, J.

Colloid Interface Sci., 80, 224 (1981).

10. P. Lianos and R. Zana, Chem. Phys. Lett., 72, 171

(1980).

11. E. Hirsch, S. Candau and R. Zana, J. Colloid

Interface Sci., 97, 318 (1984).

12. C. Gamboa and L. Sepulveda, J. Colloid Interface

140

Sci., 113, 566 (1986).

13. T. Tominaga, T.B. Stem and D.F. Evans, Bull. Chem.

Soc. Jpn., 53, 795 (1980).

14. O. Bayer, H. Hoffmann and W. Ulbricht, in

"Surfactants in Solution", Edited by K.L. Mittal

and P. Bothorel, Vol. 4, Plenum Press, New York,

1986.

15. Ch.D. Prasad and H.N. Singh, Colloids Surf., 50,

37 (1990) .

16. P.M. Linderauth and G.L. Bertrand, J. Phys. Chem.,

97. 7769 (1993) .

17. R.F. Bkeeva, S.B. Fedorov, L.A. Kudryavtseva, V.E.

Bel'skii and B.E. Ivanov, Kolloid. Zh., 46(A), 755

(1985) .

18. G.L.A. Force and B. Sarthz, J. Colloid Interface

Sci., 37, 254 (1971).

19. M. Sasaki, T. Yasunada, M. Ashide and U. Kau,

Bull. Chem. Soc. Jpn., 51. 1553 (1978).

20. V. Rajagopalan, P.S. Goyal, B.S. Valaulikar and

B.A. Dasannacharya, Phynica B., 180 & 181, 525

(1992) .

21. H.N. Singh and S. Swarup, Bull. Chem. Soc. Jpn.,

51. 1534 (1978).

CHAPTER - IV

NON-NEWTONIAN VISCOSITY MEASUREMENTS ON

CETYLTRIMETHYLAMMONIUM BROMIDE MICELLAR

SOLUTIONS IN PRESENCE OF FEW AROMATIC SALTS

AND ACIDS

142

Certain surfactants form rodlike or threadlike

(wormlike) micelles at higher concentrations and/or

when a second oppositely charged surfactant,

organic/inorganic counterion or an uncharged coit jound

is added "'*. These solutions show very striking

viscoelastic behaviour. In any case, the structure of

added molecule is of crucial inportance for the

phenomenon of viscoelasticity (see, for exanple. Table

1.1) .

Most of the investigated systems contain cationic

surfactants (with quaternary ammonium or pyridinium

head groups) combined with different types of anions

(counter or added). With halide anions the micellar

growth is gradual. However, with hydroxy-or halo

substituted anions worm like micelles grow rapidly. The

organic counterions bind nearly 100% to the micelle,

suppressing the effect of electrostatic interactions in

these systems. Not only are intermiceller interactions

damped, so are the interactions between surfactant

molecules within a single micelle. This decreases the

surfactant head group area and causes the micelles to

adopt a cylindrical rather than a spherical structure.

These micelles grow and become polydisperse with

increasing concentration, often achieving a certain

degree of flexibility. At sufficiently high

143

concentration the micelles overlap and become entangled

with each other, in a manner analogous to semidilute

polymer solutions^"^^^

Some surfactant molecules in aqueous solution are

spontaneously transformed from micelles to lamellar

array in the presence of a high salt concentration. On

a molecular scale, this change in aggregate morphology

is facilitated by an increase in counterion binding cind

dehydration of the surfactant head groups and bound

counterions. The counterion binding suppresses the

micellar charge and decreases the surface area per

surfactant molecule by reducing the electrostatic

repulsion between the head groups, thus facilitate the

micellar growth. It is well known that the shape of the

micelles depends strongly upon the actual packing

parameters in micellar assembly^^'^2_ Thg addition of

different counterions leads to large deviations of

packing parameters. The salicylate and alkyl benzoate

counterions are most efficient. NMR studies on the

cetyltrimethylammonium salicylate (CTASal) system

reveal that the ^H lines for N (0113)3 group are shifted

to higher fields and signals are broadened^^,14_ This

leads to the conclusion that the counterions

(salicylate) are strongly adsorbed at the micellar

144

surface. The salicylate ajiion orientates in such a way

that the negatively charged site (COO" group) stands

perpendicular to the itiicellar surface.

Similar conclusions can be obtained from

fluorescence measurements^^. Measurements of self

diffusion coefficients showed that about 93% of all

salicylate sticks to the micellar surface^^. This is

about twice as much as in the case of pure CI or Br

ions. Similar results can be obtained from measurements

of the surface potential^^' 17-19 j^ viscoelastic

surfactant solutions typical data are of the order of

25mvl5 This low value can be interpreted in terms of

the proposed phenomenon of surface charge condensation.

The geometry of worm like micelles in aqueous

solution has been studied by small angle neutron

scattering (SANS)20-22^ rheometry / viscometry23-26^

light scattering23,26 ^nd cryo-transmission electron

microscopy (cryo-TEM) 7,28 Cummins cind associates^O'21

concluded from their SANS data, taken from a solution

undergoing significant shear, that the micelles are

rigid monodisperse rods. This is inconsistent with the

cryo-TEM studies27,28^ in which micelles have been

found to be polydispersed long flexible ones. Besides,

one of the unanswered questions is, what interactions

cause wormlike or rodlike micelles to grow from

145

spherical? Answering this could help us understand the

kinetics of micellar and mesophase growth.

The features of \inique viscoelasticity of

CTAB/NaSal system were classified into three types

according to increasing concentration of sodium

salicylate while that of CTAB was kept constant^'29-31.

Porte and Appell32 have clearly shown that micelle

length in solutions of, for instance, cetylpyridinium

bromide (CPB) micelles in H2O - 0.2M NaiBr is reduced

upon addition of 0.2M NaCl. This result indicates that

the overall ionic strength does not alone determine the

micelle length and that the total amount of bound

counterions (which is reduced upon addition of NaCl) is

an equally important factor. Recently, the rheological

behaviour of solutions of cetyltrimethylammonium

chloride (CTAC) in the presence of sodium salicylate

and NaCl, has been investigated33. The results show

that the stress relaxation function characterizing the

system tends toward a single exponential as [CTAC]

increases and/ or tetiperature decreases. These results

are in agreement with the theory of rheological

behaviour of 'living polymer' chains^O (polymer chains

whose length varies on a time scale comparable to the

reptation time). Someinconsistencies in quantitative

146

analysis were explained on the basis of nonuniform

distribution of bound CI and salicylate ions in the

hemispherical endcaps and the cylindrical body of the

elongated micelles.

The theory of micellar growth presently lacks

strongly predictive powers, so it was believed that a

good descriptive data base of systems undergoing

micellar growth should be established.

From a chemical point of view, the salicylate

anion may show complicated adsorption properties at

micellar surface. On the grounds of the polar hydrogen

bonds between the OH- group and the neighbouring acid

group, there are other types of interactions which can

eventually influence the specific orientation at the

micellar surface. Further, such type of additives are

often used in pharmaceutical products such as

ointments, creams or lotions. Surfacteints are also used

in all these preparations. Therefore, studies on

surfactant and conpounds very similar to sodium

salicylate may be of practical inqportance. All these

facts prompted us to get a deeper insight into the

complicated phenomena of such counterion condensation

and their consequence on the viscosity behaviour of

CTAB. Attention has been focused on Sodium salicylate

and compounds having similar structure as of sodium

147

salicylate and their effect was seen on viscosity

behaviour of CTAB solutions of various concentrations.

EXPERIMENTAL

Cetyltrimethylammonium bromide (CTAB) was the same

as previously purified and used in Chapter III. Sodium

salicylate (NaSal) and sodium benzoate (NaBen) were

purchased from Aldrich Chemical Co, USA (99%) , while

salicylic acid (SA) and anthranilic acid (AA) were BDH

(99%) products. These chemicals were used as received.

All solutions were prepared by adding doubly

distilled water into weighed coir jounds. The confounds

were always totally dissolved into the solvent.

Samples were kept at fixed teit5)eratures for 48 hours in

order to attain equilibrium.

Shear viscosity (r^) measurements were performed

with a Brookf ield '* viscometer (Model DV-I+) having

sixteen speeds (0.3, 0.5, 0.6, 1.0, 1.5, 2.5, 3, 5, 6,

10, 12, 20, 30, 50, 60 and 100 rpm) . This viscometer

was equipped with a cone (either of radius 2.4 or 1.2

cm and 0.8 or 3.0 cone angle) and plate (cup) geometry.

The sample cup is jacketed and has tube fittings for

connection to a constant temperature circulating bath

(Brookfield Model TC-200). After transferring the

sair5)le to the cup, the sample was left undisturbed for

us

atleast one hour for thermal equilibrium. Then the

viscometer was started at the lowest speed (rpm) and

after 10 revolutions screen reading was recorded which

directly give rp at that speed. The viscometer speed

was changed to next higher speed setting and the value

of ng recorded in a similar way. Observations were

continued till the torque value displayed 100% or EKE

(which means above range) . In this manner T^Q values

were obtained at different shear rates.

Results

Zero shear viscosities (1^=0) were obtained by

extrapolating the %5 vs shear rate (G) plots to zero

shear. Such a typical plot for CTAB/AA system is shown

in Fig 4.1. r]p=o values for different salts and CTAB

concentrations obtained at different ten5)eratures are

compiled in Tables 4.1 and 4.2. In Fig. 4.2 the effect

of NaSal concentration on the viscosity behaviour of

CTAB solutions (of different fixed concentrations) is

shown. We Ccui see that for constant CTAB concentration

and varying salt content the viscosities show a

complicated behaviour with two maxima cmd one minimum.

Similar plots for NaBen addition are given in Fig. 4.3.

The effect of temperature is depicted in Figs. 4.4 and

4.5. The viscosity data for CTAB/SA cind CTAB/AA systems

o

0 G(s-S

100 149

200

250 500

G(s"^ )

Fig. k-} :

750

Shear viscosity (r^g) vs. shear rote plots for

0-1MCTAB micellar solutions containing various

amounts of anthranllic ocid (AA) at 25 *c .

H

3

CO

M 0)

H

3

•H Q

V m

CO

H

n)

0)

H

(0 CO

• H •0 0

CO

i 0

O II

0) •H 4J •H

n 0 u n >

M

I CO o u 0) N

o H

ITl O

A I I

O

CCO£

C\ 00

H

o VD

(N

0^

cn ro

in ID

^

n V0

^

* 00

^

H H

ID

O M

m

150

in

1

n

o c

'

'f (T\

fS

vo ^

V£) O

ro u> ^

^ H

^

r-^

vo 'J*

^ o\ ^

o 0>

o CN

in

H

m

-0

0

u

in in in m

in fs

>

rn in

m CO

m in V£>

o vo

in 00 >

U)

^

o

> >

O 00

m

rn '<'

u> H

m 00

o n

CN H

^ Oi

U> 00

in

O

o n

in CN

A 1 1

u 0

1 1

1 00 1 \0

1 H

1 cn

1 CN

1 O 1 CN

1 PO

1

o CN

CO

•

n

00 CN

CN

ro

O

•

<<

CN

ro

o

<*

t

CO

o

^ ^

^

o

in

ro

ro

H

00

m

m

CO

CN

VD

ro

H

<!

o CO

ro

o H

•

ro ro

CN

00

ro

<N

m

ro

m

o

H m

in CN

CN

ro

\0

00

ro

00

m ^ ^

ro

o m

o

m

ro 00

m H

00 CO

r-H

in

o CN

U5 O

LD

O -«<

U) o m

o n

m (N

^

LD cn

a\ H

TT

cr\ ID

LD VD

n

m '9'

ro r n

in CN

n f*

n

in n

in o ^

in (N

in H ^

o n

vo fO

'*<

o u>

10 m ^

o u>

C\ m "«f

o m *

V

a 0

u in in m in in in in in

151

in m

o rn

H H

VO O

U> c

^ o

o in

00 10

00 p*

o >

m in in in in m in in m

0\

m

CN O CN

n m

in CN

ro

o CO p-

ro

00 CO

in CO

CO ro n

H U3

CN LD

m

ro ro CO ro

in

ro ro ro ro

CO

ro

H ro ro rvj H

in o o H

CO CN

ro H

00 o

p» Oi

CN ro

ro r-

o o\

CN r«

o c

a\ CN

O H

ro

^ ka

o «x>

CO m

o V£

ro CO

in CTi

m o

o> H

ro o

O o

00 U)

(N ^

CO •<t

LD in LD m ^ ^ ^

o ro

ro t^

r-U)

<^ 00

O o

CN o

CTi O

^ CO

in vc

o <^

00 tj*

rv] CN rv) CM ro ro ro rv) CN CN M

OS CN

ro 't

ro m

in m

in m

^ ^

o o

o CO

r V£

^ ^

u> CN

CN rv]

p»

a\ ro ro ro ro ro ro ro ro ro ro ro CN

'J* V0

vo o

vo 00

o o

o H

m U)

m ^

H H

V£ o\

H >

00 V£

> in

m ro

ro ro ro ro ro ro ro ro

00

^ 0>

"t H

l>

o H

^ VC

t H H

in 00

rg ••t H

IsO !«

U9 U? H

00 H

0^ 00 H

O in

o H fS

^ t

o ro r>i

o in

o ^ fv)

O O

o m N

o CN

CO U) CN

H t

m 00 CN

00 H

00 H ro

ro ro ro ro ro

o 00

> ^ ro

o >

H VO ro

O 00 H H Vfl H O a\ ^ ^ r-\ iT) IT m

^ ^ ^ ^ m n n i

o o o m ^ H <r> 00

CO

n

o in o 0

in in ^ ^ I I ^ n

CN

in

00

n

n

m

n

o

(N H

in in I I in I ^ rn

ro I ro I I (N I

I I

o o

I 1 ^ 1 I C N I

( N I I I I I I I

in m ( N I I I I I I I

o m

n I I M I I

o o m r* n

m t^

t^ 00 m

o o o o ^

o o n CM Tj<

T}<

m ^ m ^

o o o o m

n T»<

H r> tn

o o m <N vc

152

M

H

5

V) 153

H

9

• H Q

s

0)

Id 0 N

s I

• r l

•0 0 W

I u o

n 0)

•H 4J •H 0) 0 u n

•H

> U

01

0 u 0)

o

o H

in o

A I I

fib 0

C C Q £ o rt g

O 1 ^ 1

in 1 m 1

O 1 m 1

in r<i 1

1

vo H •

H

CN If

•

H

r» CO •

H

00 in •

H 1

<ri > •

H 1

> o •

H 1

n n «

(N 1

fN in

1

1 H

in n

t

1 (N

ro CO •

1 (N

CO ro (

1 n

H n <

CM

> m •

(N

a\ CO •

1 (N

^ n

1 ro

1

1

1

CN O

Tf

VT) VC •

H

H ro •

CN

H C\

• c<

CO <!»<

ro

H CO ( cs

in o • ro

O in • n

ro o 'i*

cs r •

CN

O ^ • ro

o 00 • ro

in rj

^

V V

6

1

1

in CTi

H ro

ro c

o H I

I I I

CO

m CN

CN

ro

H in in

ro

CN CN

o in H

in CO

r>) CN

in CN)

U) 00

in >

CN O

CO t

V£ H

H 00

CN ro rv] CN

o

CN

in ro

CO

CN r j CN (N

H ^

TJ* ro

00 CN

CO U)

in ^

^ CN

m

o 00

o

CN CN CN CN

ro m

CN

1

as H

ro CO

CN

ro H

ro

H ro

ro CN

ro

O

o ro

«£ m

^ 't

o ^ vc in

o m M W

O o

in (

CN ro CO u>

r« o ^ >

in p~

a\ r-

m H

00 CO

00 ro KD o\

^ H

r* o H

't vc > H H

ro 'J'

o ro H

(N ^

O^ O

^ o

o o

o o

in 00

^ 00

0> vc

H '*<

CO n

0^ H

n t

r if)

154

rn n n n rn (N (N (N CN (N ( N

VD ID

00 ^

^ in

n ^

n ^

ffi (N

^ (N

H H

0> r»

(N r~

^ vo

00 o

o r

o ^

n n m ro n ro n n rs fN (N (N

00 CO

m n

o CO

n CO

H m o

m o H

(N 00

rO ro n ro ro f i fS

00 in o

<0 (N

VO ro

m 't

m (N

^ ro

H H

m O

P« a\

CO r>

CO 'i*

H m

00 00

ro ro

^ H

ro ro

ro ro ro ro fN (N CN

00

H

CO

rv)

00

H

H

r-H

o

o

o ro

in in

H 1

ro O

ro in

1 H

H t

ro H

H

CO (N

H

in vo

1

m H H

O H H

ro

rs M (N

vo

r ]

0^ m CN (N

VO ro

N

H H

VO

(N (N fS

00 H vo

in fM

ro

00

o ro

vo

(^

vo CO

(N CN

ro ro p-

r^

00 vo

(N fN

rs (N

CO

I I I I I I I I I I I I I I

00 r-«i(" ro vo

H H

i H l l H l H i l l l l l l l l i

t-> 00 (N r* t ^ ^ CM

H I H H I I I I I I I I

in 00

H

VO

vo vo vo H

00

o CO

H

CTl H

0\ CO H

O O

o o

m o H rs

CO

o

(N

P»

O ro

o o

o m

rs) 00 vo (N

H

m 00 rvi

CO H

00 H ro

ro 00

ro

O

o m

ro

o o

o o

m

m

o o

o o m

vo

00 ro m

o o

1

o o vo

155

5-2 -

5-6

5-2

i f - 8 -

k-k

i*-0

3-6 -

3-2

2-8

CCTAB3(M)

• 0-05

0 80 160 2kO 320 t*00

C Na Sal 3 ( mM )

i+80 560 6k

Fi'g k-2 : Zero shear viscosity (f[Q = o^°^ ° function of

sodium salicylate ( No Sai ) concentration for diff(

fixed contents of CTAB at 25'c •

15B

o II

o cr» en o

^ -

3 -

± 80 160 2i*0 320 ifOO

C Na Ben 3{ mM )

kQO 560

Fig. f f3 : Zero shear viscosity ( r |^Q_Q)asa function of

sodium benzoate ( No Ben ) concentration for

different fixed contents of CTAB at 25*C.

157

o \\

CD

en o

3-5 h

3-0 h

2-5

Temp. ('C )

0 25

• 30 • 35

• ^0

160 ifOO if80

F|*g z^-f^

2^0 320

C Na Sal 3(mM)

Zero shear viscosity Cf]^g_o ) of O-IM

CTAB m/cellar solutions as a function

Of sodium salicylate ( NIa SQI ) concen­

tration and temperature.

15S

3-6 - Temp. ( C )

0 25

150 200 250

C No Ben3(mM)

350

Fig. '+•5 * Zero shear viscosity ( r ^ ^ . Q ) of 0- lMCTAB

micellar solutions as a function of sodium

benzoate ( Na Ben ) concentration and tempe­

rature .

m

I

U 0 in rs

Id

4J

a •d •H

0 •H H •rl

Si •0 •H

U •H

•H H 10

u 0 lU

II

n 0)

•H 4J •H Cfl 0 U n •H > u n 0)

a

•H 4J •rl

o II

g'

o H

in o

o

O H

A I

14-1

CO

C 4J U - H — . C "OS Oiw-O B

uort«S

(N

CM

O in

H

in

CO

fN n

o

Tl<

rs n n

O

in in

n

o

o

00 o o

00

o

CO I

H

00 in

m in

n

n ro

o o

o n

in

^ Tf

o in

vo m

CO 1 0

00

00

H

m H

00 00

159 H P*

CO m

CO o

(N c

00 in

00 t^

o p*

00 H

H O

T3

C o u

I f

CN CS f S M

00

o O

n

00

n vo tri

o H

00 o 00

(N 00

o CO

o

IGO IT

H

LD

O 00

o CO

ro ro fN

CM 00

O O (N

CN {\ CN tN

ro U3

if) CO H

ro

o n

^ vo r* H H

> ^

o ro H

in 00

(N «}* H

vi; u; u> UJ H

CO H

0> 00 H

(N IT)

O H fS

H r* in 00 (N

I t i l

o n O

cn o

6 k

5 k

0 0

[ C T A B J ( M )

O 0-10

0-20

^0

Fig. i f -6

80 120 160

C SADCmM )

200

Zero shear v iscosi ty (r jg^Q) as a

func t ion of sal icy l ic acid ( S A )

concentrat ion for d i f fe ren t f ixed

contents of CTAB at 25"c.

162

o I I o

O

6-0

5-0

C C T A B : ( M )

•

0

\ ®

0-05

0-10

0 -20

k-0 -

3-0

2-0 -

1-0

0-0

50

Fig. i+-7

100 150 200

CAADCmM)

250 300

Zero shear viscosi ty ( r^gro^ ° ^ °

func t ion of anthrani l ic acid ( A A )

concentrat ion for d i f f e ren t f ixed

contents of CTAB at 25°C.

163

are con?)iled in Table 4.3 and are plotted in Figs. 4.6

and 4.7.

Discussion

In some dilute micellar solutions of soaps such as

CTAB, viscoelasticity can be induced by addition of

specific additives. According to the generally agreed

model^^^ the viscoelastic effect arises from the

formation of long cylinders of elongated micelles. The

resultant solutions have a gel-like structure at higher

concentrations. However, there is no clear explanation

why viscoelastic effects are brought about by some

solubilizates and not by others. Inspite of a number of

detailed studies, several aspects of the origin of

viscoelasticity have remained unanswered. For instance,

it is not clear why the cylindrical micelles grow to

several himdred angstroms length even though the volume

fraction of the surfactants is still of the order of

10~3 (at millimolar concentrations) . The transitions

shown by CTAB and CTASal as a function of concentration

are as follows :

CTAB: OmM ng>nomer o.8mM spherical micelle 270mM

cylindrical micelle 720mM liquid crystal

CTASal: OmM monomer o.lSmM cylindrical micelle 720mM

liquid crystal

164

In the case of CTASal (a) it is remarkable that

the region of spherical micelles is totally wiped

out^^, (b) the cmc is drastically reduced, and yet (c)

the transition from cylindrical micelles to hexagonal

LC phase remains the same. Why these changes occur on

replacing Br" by Sal" is not understood. These are the

some facts which are yet to be explained. In this

chapter atteti ts have been made to answer some of these

questions in light of the data obtained on CTAB - NaSal

and some other compounds similar to NaSal.

It can be mentioned that CTAB micelles in water

exhibit positive electrostatic potential. The micelles

possess a positive net charge and exhibit strong

intermiceller interaction. In addition to that,

pseudolinkages composed of short rodlike (or elliptic)

micelles are formed in dilute solutions. The

pseudolinkages between micelles increase with micelle

concentration and tighten in concentrated solutions.

With the addition of NaSal in O.XM CTAB, while

intermicellar correlation diminishes (owing to the

electric shielding) , the micelle size or rod length

increases and these long rodlike micelles entangle with

each other. This is the reason for initial steep rise

i" nG=0 as we increase the amount of NaSal. It was

reported earlier that salicylate ions can penetrate

IB5

into micelles and increase the Rp value of CTAB

molecule"*. The increase in Rp value could be understood

if it is assumed that the salicylate anion binds

strongly to the CTA"*" cation. This binding would reduce

AQ. Also, the phenyl moiety of the salicylate might be

embedded into the micellar hydrophobic region^^'^^. The

result then is the trend ellipsoidal micelles — »

wormlike (rodlike) micelles which causes the steep rise

in viscosity (Fig. 4.2). As the sites for intercalation

are saturated, viscosity reaches to maximum and further

addition of NaSal simply causes the adsorption of Sal"

in Stem layer of the micellar surface. There are two

different mechanisms by which micellar aggregates can

be formed and destroyed at low salt concentrations,

ionic micelles change their aggregation number only in

a stepwise fashion, while at higher salt concentrations

the micelles can also coalesce and break into pieces.

In a first approximation it is necessary to know only

that the stress can relax by disentanglement or by

kinetic processes and that the mechanisms are changed

as a function of the salt concentration (i.e., NaSal) .

According to these ideas, the complicated shape of the

r[G=0 curve can easily be traced back to the kinetic

properties of micellar aggregates. Therefore, beyond

166

first maxima (Fig 4.2), further addition of NaSal

destroys the intermiceller correlation (entanglement

to disentanglement) owing to the electric shielding

effect. As a result, the rheological character

diminishes in opposition to micellar growth, and the

riQ O decreases with increasing [NaSal] . After passing

the minimum, (where the viscosity is still higher than

the starting solution) , r\p=o starts to rise again and

reaches a second maximum at an excess salt

concentration {[NaSal] > [CTAB]}. The specific

adsorption and penetration are promoted by the addition

of excess of NaSal. This accelerates the growth of

rodlike micelles, which entlangle again with each other

in solutions. While the pseudonetwork con^osed of

pseudolinkages presents a rather elastic rheology

character, the pseudonetwork by entanglement has more

viscous rheology character. The latter effect seems to

be responsible for the viscosity rise upto the second

maximum. At further higher [NaSal], excess adsorption

and penetration of Sal" allow for micelles to charge

negative (charge reversal) euid to diminish

destructively to smaller sizes because of the

electrostatic repulsion among the micelles (now

negatively charged). Similar behaviour was observed

with sodium benzoate (Fig. 4.3).

IB7

When the ITG=0 ^^ investigated as a function of

surfactant concentration (Fig 4.2), the maxima and the

minima shifted to higher NaSal concentrations. In a

log-log plot we observed a single straight line (Fig.

4.8), indicating that there exists a single relation

between the concentrations of the surfactant and the

salt. From the fit of the data we obtain the relation

given below.

log[NaSal]/mM = 0.57+0.62 log[CTAB]/mM (1)

The temperature effect on the viscosities of O.IM

CTAB micellar solutions with varying [NaSal] and

[NaBen] are depicted in Figs. 4.4 and 4.5 respectively.

These results clearly dictate that only r|j3=o slightly

decreases with tenperature rise (which is very usual

ten^erature effect) but positions of the maxima and the

minima remain unaltered; this suggests that the

Theological behaviour does not change with temperature,

especially in the concentration region used in our

studies.

The viscosity behaviour of CTAB miceller

solutions in presence of salicylic and anthranilic

acids are shown in Figs. 4.6 and 4.7, respectively.

These acids have similar structures as of sodium

salicylate and toluic acid (2-methyl benzoic acid).

153

2'k U

1-6 [-

0-8

0- i f 0-8 1-2 1-6 2-0

log CSurfactant!]

2-k 2-8

Fig. ^-8 Plot of logCNaSaiJ as Q function of logCCTABJ

at viscosity maximum (f irst) of Fjg. k-2

189

0 OH

o OH

OH

N

O \ H H

OH

CH3

O

2-Hydroxybenzoic 2-Aminobenzoic acid (SA) acid (AA)

2-Methylbenzoic ac id (2 -MeHBen)

It is interesting to note that only a single peak

(though broad) is observed with both the AA and SA.

Furthermore, the peaks became broader and appeared at a

higher [additive] as we increase the [CTAB]. From

previous works^ it is known that NaSal and SA are about

equally effective in driving the transition (micellar

growth) in CTAB solutions, whereas 3- and 4- hydroxy-

benzoic acids are less ef fective *'- . Further, the

effectiveness of the acids is depleted as -OH group

moves clockwise on the benzene ring. It was shown

earlier that the rheological properties depend strongly

upon molecular details of the added coirpound, e.g., a

methyl group in the 4-position of NaBen gives solutions

with high viscosities and if the -CH3 group moves

anticlockwise on the benzene ring the viscous

resistance decreases and exhibits pure Newtonian flow

in the case of -CH3 group positioned in the vicinity

of the polar acid group (2 - methyl NaBen) 25^ We can

170

see that the effective electric charge on the polar

acid group may be affected by the presence of other

groups on the benzene ring. In case of SA, the lone

pair of electrons is easily transferred to the acid

group through benzene ring than in the case of 2-

MeHBen. The case of AA comes in between the two above

mentioned acids as the lone pair of electrons can

transfer to polar acid group with less ease than with

the case of SA. The process of such a shift in electric

charge (or cloud) due to the presence of another

neighbouring group will contribute remarkably as a

positively charged micelle is available for their

embedding as well as for electrostatic interactions.

Therefore, the viscous resistance could be expected

with cationic micellar solutions containing SA in the

system. This indeed was observed in I1G=O values given

in Table 4.3. The reason of appearance of the maximum

at a higher concentration of AA (as compared with the

CTAB/SA system) may also be the same as more number of

AA molecules are required to neutralize the same

micellar charge. The behaviour of these acids is

different than the NaSal or NaBen as only a single

peaked behaviour was observed (Fig. 4.6 & 4.7). This

may be due to the fact that with these acids

electrostatic interactions are not that much strong as

171

the case with NaSal or NaBen. These acids interact, in

the first approximation, due to a combined effect of

electrostatic and hydrophobic forces with the micelle

and, after saturation of the palisade layer, they can

get adsorbed at the surface of the micelle only. This

latter effect is responsible for the fall of viscosity.

The charge reversal effect may not be considered as

strong here as with NaSal or NaBen. It may be concluded

then that the effect of additional group on the benzene

ring (position and chemical structure) plays an

important role in the interaction of the polar acid

group with the cationic micelles. The punning of more

charge on the acid group by the presence of favorable

groups (e.g., in presence of more -OH groups on the

ring) may enhance the micellar growth. This point is

worth exploring and may open up a new area of research.

Interestingly, so far salicylate, alkyl benzoate or

their acid forms were studied for such interesting

Theological studies. Here, it is shown that the same

effect is observed even in presence of -NH2 group on

the benzene ring. Thus, the role of lone pair of

electrons or, more specifically, the effective charge

in?)arted by a group to polar acid counterions, seems to

play a special role in the micellar growth.

172 REFEKEBTCES

1. s. Gravsholt, J. Colloid Interface Sci., 57, 575

(1976) .

2. H. Rehage and H. Hoffmann, Rheol. Acta, 21, 561

(1982).

3 . T. S h i k a t a , H. H i r a t a and T. KotaJca, Langrauir, 3 ,

1081 (1987) .

4. z. Lin. J.J. Cai, L.E. Scriven and H.T. Davis, J.

Phys. Qiem., 98, 5984 (1994) and references

therein.

5. S.J. Candau, F. Merikhi, G. Waton and P.

Letnarechal, J. Phys. (Paris), 51. 977 (1990).

6. H. Rehage and H. Hoffmann, J. Phys. Chem., 92, 4217

(1988).

7. M.E. Gates, J. Phys. Chem., 94, 371 (1990).

8. T.A. Striven, Colloid Polym. Sci., 267, 269 (1989).

9. T. Shikata, H. Hirata, E. Takatori emd K. Osaki,

J. Non-Newtonian Fluid Mech., 28, 171 (1988).

10. M.E. Gates, Macromolecules, 20, 2289 (1987).

11. H. Hoffmann, Adv. Colloid Interface Sci., 32 , 123

(1990).

12. J.N. Israelachvili, D.J. Mitchell and B.W. Ninham,

J. Chem. Soc, Faraday Trans. 2, 72, 1525 (1976).

13. B. Lindman, M.C. Puyal, B. Bum and G. Gunnarsson,

J. Phys. Chem., 86, 1702 (1982).

14. U.R.K. Rao, C. Manohar, B.S. Valaulikar and R.M.

Iyer, J. Phys. Chem., 91, 3286 (1987).

15. N.C. Verma, B.S. Valaulikar and C. Manohar, J.

173

Surf. Sci. Technol., 3, 19 (1987).

16. U. Olsson, O. Scxierman and P. Guering, J. Phys.

Oiera., 90. 5223 (1986).

17. M.S. Fernandez and P. Fromherz, J. Phys. Chem., 81,

1977 (1977) .

18. M. Montal and C. Gihen, Bioenergetics, 4, 4 (1973).

19. J.W. Larsen and L.B. Tepley, J. Org. Chem., 41.

2968 (1976).

20. P.G. Cutratiins, E. Staples, J.B. Hayter and J.

Penfold, J. Chem. Soc, Faraday Trans. 1, 83. 2793

(1987) .

21. J. Penfold, E. Staples and P.G. Cummins, Adv.

Colloid Interface Sci., 34. 451 (1990).

22. J. Marignan, J. Appell, P. Bassereau, G. Porte and

R.P. May, J. Phys. (Paris), 50, 3553 (1989).

23. S.J. Candau, E. Hirsch, R. Zana and M. Adam,

J. Colloid Interface Sci., 122. 430 (1988).

24. T. Imae, M. Sasaki and S. Ikeda, J. Colloid

Interface Sci., 127, 511 (1989).

25. H. Rehage and H. Hoffmann, Mol. Phys., 74, 933

(1991).

26. S.J. Candau, E. Hirsch and R. Zana, j. Colloid

Interface Sci., 105. 521 (1985).

27. T. Clausen. P.K. Vinson, J.R. Minter, H.T. Davis,

Y. Talmon and W.G. Miller. J. Phys. Chem., 96. 474

(1992) .

8. 28. Z. Lin, L.E. Scriven and H.T. Davis, Langrauir,

174

2200 (1992) .

29. T. Shikata, H. Hirata and T. Kotaka, Langmuir, 4,

354 (1988).

30. A. Koike, T. Yamamura and N. Nemoto, Colloid

Polymer Sci., 272, 846 (1994).

31. N. Nemoto, M. Kuwachara, Ming-L. Yao and K. Osaki,

Langmuir, 11. 30, (1995).

32. G. Porte and J. Appell, in "Surfactants in

Solution", Edited by K.L. Mittal and B. Lindman,

Plenum Press, New York, Vol. 2, p.804, 1984.

33. F. Kern, R. Zana and S.J. Candau, Langmuir, 7, 1344

(1991).

34. J.R. Van Wazar, J.W. Lyons, K.Y. Kim and R.E.

Colwell, "Viscosity and Flow Measurements",

Interscience, New York, 1963.

35. H. Hoffmann, G. Platz, H. Rehage, W. Schorr and

W. Ulbricht, Ber. Bunsenges. Phys. caiem., 85, 255

(1981).

36. J. Ulmius and H. Wennerstrom, J. Magn. Reson., 28,

309 (1977) .

37. T. Shikata, H. Hirata and T. Kotcika, Langmuir, 5,

398 (1989) .