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O R I G I N A L A R T I C L E
Interaction of Azo Dye with Cationic Surfactant Under DifferentpH Conditions
Muhammad Faizan Nazar Syed Sakhawat Shah
Muhammad Arshad Khosa
Received: 27 October 2009/ Accepted: 4 December 2009 / Published online: 22 January 2010
AOCS 2010
Abstract The aggregation induced by Alizarin Yellow R
(AYR) in the cationic surfactant, cetyltrimethylammoniumbromide (CTAB), was investigated by measuring their
UVvisible absorption spectra. Conductance measurements
as a function of surfactant concentration below and above
the critical micelle concentration (CMC) were studied.
CTAB aggregation takes place at the concentration far
below its normal CMC in the presence of AYR. Both
hydrophobic and electrostatic interactions affect the
aggregation process in aqueous solution. The dye effect on
the CMC of CTAB was noted by a specific conductivity
method as well. AYRCTAB binding constant (Ks) and
watermicelle partition co-efficient (Kx) were quantified
with the help of mathematical models employed to deter-
mine the partitioning of organic additives in the micellar
phase. The number of dye molecules per micelle was
estimated at particular CTAB concentrations above CMC,
during this study.
Keywords Alizarin Yellow R Cationic surfactant Specific conductivity Hydrophobicity Partition coefficient Binding constant
Introduction
Amphiphilic properties of surfactants have attracted
growing attention for their use in biological and chemical
research applications especially in the dyeing process
where the role of surfactants is very important [1]. Micelles
are aggregates formed by amphiphilic molecules (hydro-phobic chain and hydrophilic head group) above their
critical micelle concentration (CMC). They are composed
of a hydrophilic surface and a hydrophobic core. This
specific micellar structure shows chemical interactions
with hydrophilic or lipophilic molecules [2] that can be
applied in analytical chemistry as well as pharmaceutical
industries. The structure of micellar aggregates is of par-
amount interest in several industrial applications of sur-
factants. One of the most fundamental properties of
aqueous micellar solutions is their ability to solubilize a
wide variety of organic solutes with quite distinct polarities
and degrees of hydrophobicity. Among various contribut-
ing factors, the favorable (hydrophobic) sites of organic
additives are supportive for their readily solubilization in
the micellar aggregate [3, 4]. Surfactantsdye associations
are significant in both dyeing processes and detergency [5].
This surfactantdye interaction also customizes the uptake
of dye into substrate such as cellulose and keratin fiber [ 6].
In this study, the amphiphilic azo dye (Alizarin Yellow
R) was used as an organic additive made by the di-azo
coupling reaction. This azo dye is a pH indicator and its
ion-association complex of nickel in the presence of
polysorbate 80 had been successfully applied to the micro
determination of Ni(II) in pharmaceutical samples [7]. This
dye could be used for the determination of formaldehyde in
water samples [8]. It is also effective as a specific adsor-
bent for the removal of aluminum from both drinking and
dialysis water [9]. The intra-molecular hydrogen bonding
between the alcoholic (OH) group at position-1 and acidic
oxygen produces a stable six-member ring system
(Scheme 1). Therefore, as a result, intra-molecular hydro-
gen bonding makes dye molecules more hydrophobic; this
is responsible for their incorporation into the micelle and
M. F. Nazar S. S. Shah M. A. Khosa (&)Department of Chemistry, Quaid-i-Azam University,
Islamabad 45320, Pakistan
e-mail: [email protected]
123
J Surfact Deterg (2010) 13:529537
DOI 10.1007/s11743-009-1177-8
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for the increase in the number (n) of dye molecules
incorporated per micelle.
In this work, the conductivity measurements for critical
micelle concentration (CMC) values and UVvisible
spectral measurements for spectral changes are reported to
explain the CTABAYR interaction under different pH
conditions. The aggregation behavior of CTABAYR in
water was studied using simple spectroscopy, differential
spectroscopy, and conductivity. The micellewater parti-
tion coefficient (Kx), standard free energy change of solu-
bilization (DG0p), AYRCTAB binding constant (Ks) and
the number of dye molecules per micelle solution (n) were
calculated by employing the absorbance, differential
absorbance and conductivity data at 25 C.
Experimental
Materials
CTAB was purchased from Sigma Chemical Co., Alizarin
Yellow R [5-(4-nitrophenylazo) salicylic acid] was
obtained from Fluka. A 10 mM solution of AYR was
prepared by weighing exactly 0.144 g of reagent and the
solution was diluted up to 50 cm3 with doubly distilled
water. Other solutions were prepared by dilution. All
experiments were carried out with analytical reagent grade
chemicals using both distilled and demineralized water.
The dye used in the present study obeys Beers law in the
employed concentration range and the solution pH was
adjusted using phosphate buffer.
Procedure
UVVisible Spectroscopy
Spectrometric measurements were performed on a Perkin-
Elmer Lambda 20 ultravioletvisible spectrophotometer
with 1.0-cm quartz cells at a temperature of 25.0 0.1 C.
Differential absorbance measurements were made in such a
way that the additive solution of a particular concentration
was kept on the reference side and the surfactantdye
solution on the sample side in the spectrophotometer.
Conductivity Experiments
Critical aggregation concentrations were determined by
conductivity experiments. The specific conductance ofsurfactant solutions with and without additive (AYR) was
measured on a Microprocessor Conductivity Meter (WTW
82362 Weilheim) fitted with an electrode (WTW
06140418). The CMC of CTAB in water and in the pres-
ence of additive was determined by plotting the specific
conductance against the surfactant concentration (Cs).
Solutions in the conductivity cell were stirred magnetically
while a thermostat was used to maintain the temperature at
25.0 0.1 C.
NN
OH
OHO
NN
O
OO
O2N
H
O2N
NN
O
OO
O2N
NN
OH
OO
O2N
Monoanionicforms
Dianionicform
H H
H
pKa
= 5.0 pKa = 11.0
H
NBr
(1)
(2)
Scheme 1 1 Molecular structures of Alizarin Yellow R; 2 Cetyltrimethylammonium bromide
530 J Surfact Deterg (2010) 13:529537
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Results and Discussion
Absorption Spectra of Alizarin Yellow R Under
Different pH Conditions
Alizarin Yellow R is a poly-functional molecule with pKavalues 5.0 and 11.0 (Scheme 1, [7]). This azo dye is
slightly soluble in water in a strong acidic medium (pH 1 or2) while the functional groups of carboxylic acid and
phenol are not ionized. AYR is in mono-ionic form at
pH\ 4.5, while it shows di-anionic behavior at pH[ 10.
The aqueous solubility increases due to ionization of the
carboxylic group (pKa = 5.0) at pH 4.4 and the phenate
form is dominant in an acidic medium. UVvisible spectra
of Alizarin Yellow R have been shown in Fig. 1. A strong
bathochromic effect (kmax = 373 to kmax = 492 nm) can
be seen at pH 12.0. In a sufficiently strong base (above pH
10.0), the di-anion is formed on account of ionization of the
carboxylic as well as the hydroxyl group (Scheme 1).
Alizarin Yellow R experiences a bathochromic shift from373 to 493 nm due to extensive delocalization of negative
charges, and no change in absorption maxima from 4.5 to
10.0 pH range was observed because intra-molecular
H-bonding plays a role in keeping the kmax at 373 nm as in
an aqueous solution.
Aggregation Behavior of CTABAlizarin Yellow R
Absorption spectra of azo dye (AYR) were also recorded at
different concentrations of CTAB in aqueous solution
(Fig. 1). A particular type of dyesurfactant aggregation is
observed when the anionic component is a dye molecule in
combination with a cationic surfactant (CTAB). Low
concentrations of CTAB shift the band from 372 nm to a
new band at 388 nm and increase the intensity of the
shifted band with an increase in the concentration of
CTAB.
At very low CTAB concentration, the AYR band-I
intensity initially decreases and then increases with
increases in CTAB concentration. The process is shown in
Fig. 2.
The initial decrease in intensity of band-I is due to the
self-aggregation of dye molecules assisted by the surfactant
chain [10]. Dyesurfactant interaction below CMC allows
the dye to absorb light favorably; hence absorbance is
enhanced in the sub-micellar region. The leveling off the
curve above the surfactant CMC reveals a maximum sol-
ubilization of dye molecules within the micelle. A pro-
posed mechanism to explain CTABAYR interaction is
shown in Fig. 3.
The increase in absorbance is a result of the stabilization
of AYR by the positive charge of the monomers of CATB
as shown in the Fig. 3a. As it proceeds to the post-micellar
region, the AYR solubilization in quaternary ammonium
solution takes place initially by absorption at the micellar-
water interface replacing water molecules and thereafter
solubilization of additional dye occurs in the palisade layer
(Fig. 3b). Spectra of both di-anionic AYR (pH 12.0) and
neutral AYR (pH 4.0), experience significant bathochromic
shifts (kmax) of 40 and 20 nm, respectively, in the presence
of CTAB. Dyemicelle interaction is better explained by
quantifying its magnitude by determining the dyemicelle
partition coefficient (Kx), dyesurfactant binding constant
(Ks), standard free energy of solubilization (DG0p) of dye in
micelles and approximate numbers of dye molecules per
micelle. In the case where molecular interactions with its
300 400 500 600
0.0
0.1
0.2
0.3
0.4
0.5
0.6
absorbance
wavelength (nm)
max= 492
(a)
max = 373(d)
(c)
(b)
300 350 400 450 500
0.1
0.2
0.3
0.4
absorbance
wavelength (nm)
12
34 5
67
8(I)
Fig. 1 Absorption spectra of Alizarin Yellow R: a pH 4.0; b pH 6.6;
c pH 10.0; dpH 12.0 and Effect of CTAB on the absorption spectrum
of Alizarin Yellow R in aqueous solution at 25 C; I without
surfactant; 1 0.7 mM; 2 0.8 mM; 3 0.9 mM; 4 1.0 mM; 5 2.0 mM; 6
3.0 mM; 7 4.0 mM; 8 8.0 mM; Reference solutionwater; the
cuvette is 1 cm long
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surrounding environment are intrinsically related to spec-
tral characteristics, their changes are used for the deter-mination of corresponding partition coefficients and the
approximate number of dye molecules per micelle.
The approximate number of dye molecules incorporated
into a single micelle (n) is calculated by the following
relations [11, 12]:
n Cm
M1
M Cs CMC
N
2
where Cm is the concentration of dye solubilized in the
micelle, M is the micelle concentration, Cs is the total
surfactant concentration and N is the mean aggregation
number of micelles at CMC in water. The normal CMC of
the CTAB is 0.9 mM [13]; Cm is the concentration of
solubilized dye that is determined as [14]:
Cm Ao A
eo em3
where Ao is the absorbance of dye solution without sur-
factant, A is the absorbance at any point in the presence of
surfactant above the CMC, eo is calculated from Ao, and emis determined at higher surfactant concentration above the
CMC when absorbance of the dyesurfactant solution
0.000 0.001 0.002 0.003 0.004
0.30
0.32
0.34
0.36
Amax
CS (mol/dm3
)
A
370
375
380
385
390
395
max
Fig. 2 Relation between absorbance of (CTAB ? dye) and surfac-
tant concentration
N
NN
OH
OO
O2N
(a)
N
N
N
N
N
NN
N
N
N
N
N
NN
HOO
O
NO2
NN
OHO
O
O2N
(b)
Fig. 3 Proposed mechanism of
action of AYR in different
concentration regions of CTAB.
a Interaction of AYR with
CTAB in its monomeric form
clearly indicate that an
attractive force is present.
b Interaction of AYR with
CTAB micelle
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becomes almost constant. The micellar aggregation number
used for CTAB is 80 [15]. For a particular concentration of
CTAB (Cs), a higher value of n shows greater hydro-
phobicity of Alizarin Yellow R in aqueous solutions. The
results are shown in Table 1.
Dye molecules can aggregate either in a parallel or in a
head-to-tail fashion. A blue shift in the absorption band is
observed in the case of parallel dimeric aggregation dye
and head to tail assemblage of the dimeric dye leads to a
red shift in the absorption band as compared to the
monomeric dye [16]. In our spectrometric study, a new
absorption band of surfactantdye aggregate is red-shifted
with respect to the absorption band of the dye in aqueous
solution; and this indicates that dye molecules are aggre-
gated in a head-to-tail fashion. An AYR dye molecule that
binds to a cationic surfactant creates a more hydrophobic
binding site and facilitates the binding of another dye
molecule. This implies that hydrophobic stacking of aro-
matic parts of the azo dye is also important in the aggre-
gation process besides electrostatic interactions.
Differential Absorbance
Differential absorption spectra of dye (AYR) in the pres-
ence of various concentrations of CTAB at pH 6.6 and 10.0
are shown in Fig. 4.
Elevated values of DA with increasing surfactant con-
centration correspond with the enhanced solubilization of
AYR molecules in the micelles. Solubilized dye molecules
are distributed according to their polarity between the
highly non-polar central region and the relatively polar
interfacial region of the micelles [17, 18]. A useful physical
parameter to quantify ARY solubilization in different
micellar media is partition coefficient Kc (dm3 mol-1). It
can be calculated by the following equation [19]:
1
DA
1
KcDA1Ca Cmos
1
DA14
Ca denotes dye concentration, Csmo represents Cs - CMC0
(CMC0 is the CMC of surfactant in water), DA? is the
differential absorbance at the infinity of Cs and Kc is
obtained through intercept and slope values from the
straight line by plotting 1/DA against 1/(Ca ? Csmo), as
shown in Fig. 5a and the value of Kc has been shown in
Table 2. The dimensionless partition coefficient Kx is
related to Kc as Kx = Kcnw, where nw is the number of
moles of water per dm3, and is reported in Table 2. The
standard free energy change of the transfer of additive,
DG0p from bulk water to micelle can be calculated using the
following relation:
DG0p RTln Kx 5
Here T is absolute temperature and R is the gas constant.
The value of DG0p for the dye, using Kx is reported in
Table 2.
The high negative value of DG0p indicates the ease of
penetration of the dye into the micelles. A dye molecule
does not penetrate deeply enough into the micelle unless
the dyes hydrophobicity is sufficiently strong enough to
Table 1 Number of AYR molecules incorporated per CTAB micelle
in various pH ranges, at 25.0 C
pH A0 Cm(mol/dm3)
em(dm3/
mol cm)
M
(mol/dm3)
n = Cm/M
4.0 0.3617 1.98 9 10-5 19,225 4.25 9 10-6 5
6.6 0.3567 2.24 9 10-5 17,389 4.25 9 10-6 5
10.0 0.2333 1.75 9 10-5 14,400 4.25 9 10-6 4
12.0 0.4655 1.48 9 10-5 23,018 4.25 9 10-6 3
-0.12
-0.06
0.00
0.06
0.12
A
wavelength (nm)
(a)
300 350 400 450 500
-0.05
0.00
0.05
0.10
0.15
A
wavelength (nm)
(b)
300 350 400 450 500
Fig. 4 Differential absorption spectra of Alizarin Yellow RCTAB at
different pH; a pH 6.6, b pH 10.0 (Arrow indicates the wavelength
used for analysis)
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overcome the electrostatic interaction with the head group
of CTAB [20]. This is clear from the high values of Kx and
more negative DG0pfor AYR, as shown in Table 2.
It is assumed that Alizarin Yellow R forms a complex
with CTAB in the bulk of the solution via electrostatic
interactions before it penetrates into micelles. At first,
adhesion of the dyesurfactant complex to the micelle
surface takes place and then dye molecules reorient
themselves into the inner hydrophobic portion of the
micelles and finally it make their way deeper into the
interior (core) of the micelle. The structure of the additive
molecule (AYR) and charge on the surfactant contribute
largely towards the phenomenon of solubilization. In
addition to the hydrophobic interactions, electrostatic fac-
tors play an important role in binding of AYR to the
micelle of CTAB. The formation of an ion-pair complex
between anionic Alizarin Yellow R and the positive head
group of CTAB micelles was confirmed by the initial
absorbance changes. The initial rapid reaction may be
represented as [21]:
0 2 4 6 8 10
3.0
4.5
6.0
7.5
9.0
10.5
1/A
(Ca+Csmo
)-1
x102dm
3mol
-1
pH 4.0
pH 6.6
pH 10.0
pH 12.0
(a)
0
2
4
6
8
10
12
12
(Ca)(C
s)x10-7/A
Cs x 10-4
(mol dm-3
)
pH 4.0
pH 6.6
pH 10.0
pH 12.0
(b)
0
5
10
15
20
25
30
St/So
M x 10-5
(mol dm-3)
pH 4.0
pH 6.6
pH 10.0
pH 12.0
(c)
0 15 30 45 60 75 90
0 2 4 6 8 10
7.2
7.6
8.0
8.4
8.8
9.2
1/A
[Csmo- kCa + (1+k)Caj]
-1 x102dm3mol-1
(d)
0 2 4 6 8 10
Fig. 5 a Plot of inverse of differential absorbance (1/DA) versus
(Ca ? Csmo)-1 for 1FuE and concentration of CTAB in different
media; b Relationship between (Ca 9 Cs)/DA for AYR and concen-
tration of CTAB in various pH ranges; c Relationship between
relative solubility of AYR and CTAB micellar concentration in
various pH ranges; d Relationship between 1/DA and 1Cmos kCa1kCajfor CTAB in the presence of AYR
Table 2 Values of Kc, Kx, Ksand DG0p of Alizarin Yellow R
in micellar solution of cationic
surfactant (CTAB) in various
pH ranges
pH Kc (dm3 mol-1) Kx DG
0p (kJ/mol) K s (dm
3 mol-1) De (dm3 mol-1 cm-1)
4.0 1.55 9 104 8.6 9 105 -33.85 7,517 7,883
6.6 3.23 9 103 1.8 9 10
5-29.98 2,020 7,110
10.0 1.95 9 103 1.1 9 105 -28.76 1,267 9,513
12.0 1.75 9 103 9.7 9 104 -28.45 1,256 17,039
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AYR + CTAB ion-pair complex
In order to calculate AYRCTAB binding constant, a
quantitative approach is provided by the following relation
[21]:
AYR T CTAB
DA
CTAB
Del
1
KsDel6
where [AYR]T is the total dye concentration (Ca), [CTAB]
is the molar surfactant concentration (Cs), DA is the dif-
ference in absorbance between the complex and AYR
obtained from the differential absorbance spectrum, De is
the difference in absorption coefficients and l is the path
length (1.0 cm). To test the validity of Eq. 6, the left-hand
side term in the equation was plotted against [CTAB] in
different media, which was found to be fairly linear
(Fig. 5b).
From the slope and intercept of the straight line, values
of the binding constant (Ks) and De were calculated and are
reported in Table 2. To identify the position or location ofsolubilized dye molecules in the micelle, it is useful to
calculate the binding constant and partition coefficient of
AYRCTAB in various pH ranges. The results (Table 2)
indicate that the partition of AYR into the micelle with its
hydroxyl and carboxylic moieties near the watermicelle
interface takes place in such a way that it leads to depro-
tonation and thus making it a charged molecule. This
phenomenon facilitates insertion of an azo ring into the
core of the micelle.
Decreased pH of the medium (acidic medium) causes
protonation of the ionizable carboxylic group of AYR,
leading to elevated hydrophobicity and finally aggregationresults. In this way more hydrophobic additives are buried
deeply inside the core of micelles at a lower pH value.
Conversely, additives with hydrophilic interactions are
oriented near the surface region of the micelle. Neutral
species, mono and di-anionic forms of AYR, bind to CTAB
showing a strong pH effect on the binding constant. Using
partition coefficient (Kx) values obtained from differential
absorbance method, the relative solubility (St/So) of AYR
in various pH ranges can be obtained by employing the
relationship [22].
St=So 1 KxvM 7
St and So are total and intrinsic water solubility values,
respectively, m is the partial molal volume of the micelle
that in case of CTAB is 0.3654 dm3 mol-1 [15], and M is
micellar concentration and is given by well-known rela-
tionship in Eq. 2. Relative solubility of Alizarin Yellow R
increases with the increase of micellar concentration and its
hydrophobic interactions within the micelles. This implies
that relative solubility depends upon the hydrophobicity of
the additive molecules which is also shown by partition
coefficient values. In addition, either acidic or basic media
also affect the relative solubility (Fig. 5c).
Conductivity Experiments
The critical micelle concentration of CTAB in aqueous
solution containing AYR was determined by plotting the
specific conductance against the surfactant concentration(Cs), shown in Fig. 6a. Conductance experiments were
carried out at pH[ 10 to maximize the azo dye (dianionic
form) solubility in aqueous solution by using phosphate
buffer. Small amounts of organic additives may produce
marked changes in the CMC in aqueous media [17].
The critical micelle concentration of CTAB decreases
linearly with increases in concentration of AYR dye as
shown in Fig. 6b. This indicates that the CMC is a function
of additive concentration (Ca) and its depression by adding
solubilized material is due to a greater degree of interaction
between the hydrophobic group of the surfactant and the
hydrophobic chain of the additive used. In addition,a strong
0 1 2 3 4 5
0
30
60
90
120
Specificconductance(S/cm)
Cs x 10-3
(mol dm-3)
no dye
0.1mM dye
0.5mM dye
0.7mM dye
1.0mM dye
(a)
0.0 0.2 0.4 0.6 0.8 1.0
7.6
8.0
8.4
8.8
9.2
9.6
CMCx
10-4(mol/dm3)
Ca x 10-3 (mol/dm3)
(b)
Fig. 6 Effect of concentration of dye on the CMC of CTAB, at
25.0 C; a Specific conductance versus concentration of CTAB,
b CMC of CTAB as a function of AYR concentration (C a)
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oppositely charged attractive force between the di-anionic
form of the azo dye and the cationic surfactant CTAB on
the stern layer of surfactant is responsible for a declining
CMC of CTAB. Discussing this more quantitatively, the
entropy of the mixing dye in micellar solution causes a
reduction in the free energy of micelles in addition to
hydrophobic interactions; hence the CMC is lowered [23].
The watermicelle partition coefficient Kc (dm3 mol-1) of
AYR is calculated by using an improved relationship given
in [19]; this gives a relatively precise approximation
introducing two new factors j and k into Eq. 4:
1DA
1KcDA1 Cmos kCa 1 kCaj
1DA1
8
In the above equation, k can be obtained by plotting the
CMC of CTAB against different dye concentrations as
shown in Fig. 6b. Slope of line through CMCo (dCMC/
dCa) provides k as given in Table 3, whereas j is the
fractional amount of solubilized organic additive of total
added organic additive in the solution. Factor j becomes
zero at a certain Ca in the premicellar region up to the
CMC and increases with increasing Cs above the CMC. As
Cs increases up to infinity, j approaches unity, since
virtually all the added organic additive has been solubilized
in micelles Cma ffi Ca Thus, we can write:
j DA=DA1 9
By plotting 1/DA against 1=Cmos kCa 1 kCaj,
intercept and slope of the straight line give the value of Kcas shown in Fig. 5d.
The partition coefficient obtained from Eq. 8 and the
standard free energy change is calculated from Eq. 5, as
reported in Table 3.
There seems to be agreement between Kc values deter-
mined by Eq. 4 at constant AYR (Ca) and those determined
by Eq. 8 in a variable concentration (Ca) of AYR in pres-
ence of a higher surfactant concentration region (Cs). The
standard free energy change (DG0p) is shown in Table 3. It
was found that Kc is independent of both Cs and Ca in such a
low Ca region whereas j and kare slightly dependent on Ca.
Conclusion
Different parameters obtained from spectroscopic mea-
surements and conductance data indicate an enhanced
solubility of AYR dye in the micellar region. Intra-
molecular hydrogen bonding within the dye molecule
effectively reduces intermolecular attraction, thereby
increasing solubility in non-polar solvents (micelles).
Medium effects on the position of the long wavelength
absorption band of the azo dye characterize it as a pH
chromic reporter molecule. A partitioning study of the
solubilized system provides useful insight into the processof solubilization that is applicable to the general problem
of membrane solubilization properties and in drug delivery
to quantify the degree of drug-micelle interaction. The
partition coefficient value obtained is important in micellar
electrokinetic capillary chromatography and high pressure
liquid chromatography (HPLC) for drug quality control.
Thus, interaction with micellar aggregates induces signifi-
cant pKa shifts of Alizarin Yellow R that can be rational-
ized in terms of the partitioning of species and electrostatic
contribution. Likewise, knowledge of the effects of organic
additives on the CMC of surfactants is used both for the-
oretical and practical purposes because some additives arelikely to be present as impurities or byproducts in the
manufacturing of surfactants and their presence may cause
significant differences in supposedly similar commercial
surfactants.
Acknowledgments The financial support of the Quaid-i-Azam
University and the Higher Education Commission of Pakistan is duly
acknowledged.
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Table 3 Partition coefficient (Kx) and Standard free energy change
of penetration (DG0p) of dye (AYR) in aqueous micellar solution
(using Eq. 8)
k= dCMC/dCa j Kc (dm3 mol-1) Kx DG
0p (kJ/mol)
-0.1639 0.78 3.28 9 103 1.82 9 10
5-30.00
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Author Biographies
Muhammad Faizan Nazar obtained his masters degree in chemistry
from Quaid-i-Azam University Islamabad, Pakistan in 2005. He
obtained his M.Phil. in 2007 from the same institute. He is a Ph.D.
student of the Chemistry Department at Quaid-i-Azam University,
Islamabad. His research interests are synthesis and characterization of
microemulsions and their applications in drug delivery systems, as
well as electronic and hydrophobic interactions in dye-surfactant
aggregates.
Syed Sakhawat Shah obtained his masters degree (chemistry) in
1971 and M.Phil. (chemistry) degree in 1973 in Pakistan. He
specialized in colloids and surfactants and obtained his Ph.D. in
chemistry in Germany in 1978. He received the award of the
presidents pride of performance in 2003 and is now a professor of the
Chemistry Department at Quaid-i-Azam University, Islamabad,
Pakistan. His research interests include micellar drug delivery system,
colloidal interactions, separation and purification techniques using
surfactants.
Muhammad Arshad Khosa obtained his M.Sc. in chemistry from
Bahaudin Zakariya University, Multan Pakistan in 1994. He com-
pleted his M.Phil. degree in 2005. He is currently a Ph.D. student at
the chemistry department, Quaid-i-Azam University, Islamabad,
Pakistan. His research interests include the removal of pollutants
from aqueous solutions by micellar enhanced ultrafiltration tech-
niques and spectroscopic studies of dye-surfactant interactions.
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