7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
1/46
COLLOI DS
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
2/46
Collo id a l Disp e r s ion s
Dispe r sed sys t em s con s is t o f :a) particulate matter (dispersed phase).
b) dispersion medium (continuous medium).
Clas s i fica t ion o f d i spe r sed sys t em s ( a cco r d i n g t o
pa r t ic le s i ze ) :
MOLECULAR
DISPERSION
COLLOIDAL
DISPERSION
COARSE
DISPERSION
- Less than 1 um
- Particles undergorapid diffusion e.g. O2
& glucose
- 1 um to 500 um
- Very slow diffusione.g. colloidal silver sol.
- Greater than 500 um
- Dont diffuse
e.g. suspension &emulsion
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
3/46
Col lo id a l D isper s ions
MOLECULAR
DISPERSION
COLLOIDAL
DISPERSION
COARSE
DISPERSION
-Particles invisiblein electron
microscope.
-Pass throughsemipermeablemembranes and
filter paper.
-Particles resolvedby electron
microscope.
- Pass throughfilter paper but not
pass throughsemipermeable
membrane.
-Particles arevisible under
ordinarymicroscope.
- Do not passthrough filter
paper or
semipermeablemembrane.
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
4/46
Typ es o f co llo id a l sys te m s:
o According to the i n t e r ac t i on between particles ofdispersed phase & those of dispersion medium:
1) L y o p h ilic ( so lv en t lo v in g ) .
2 ) L y o p h o b ic ( s o lv en t h a t in g ) .
3 ) A s s o cia t io n (a m p h ip h ilic) .
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
5/46
N.B.
DISPERSION MEDIUM = SOLVENT.
DISPERSED PHASE = MATERIAL = COLLOIDALPARTICLES.
SOL. = COLLOIDAL SOLUTION.
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
6/46
1) Lyop h i lic col lo id s
Colloidal particles interact to an appreciable extent with the molecules of the
dispersion medium ( s o lv e n t lo v i n g ) .
Obtained simplyby dissolving the material in the solvent ( due to the highaffinity).
Typ es of lyop h i lic col loids ;
(Accord ing to type o f so lven t )
Hydr oph i li c co l lo ids ;
Solvent: w a t e r .
Example: acac i a ,i n s u l in . in wa t e r .
Lipo ph i li c co l lo ids ;
Solvent: n o n - a q u e o u s ,o r gan i c so lven t .
Example: r u b b e r
&polys tyrene .
S O; m a t e r i a l t h a t f o r m l y o p h il ic co l lo id i n a c e r t a in s o l v e n t m a y n o t d o s o
in a n o t h e r s o l v e n t , e.g.; acacia + water lyophilic colloid (hydrophilic type).
acacia + benzene NO lyophilic colloid formed.
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
7/46
1 ) Ly o p h i l ic co l l o i d s
o the dispersed phase does not precipitate easily
o the sols are quite stable as the solute particlesurrounded by two stability factors:
a- negative or positive chargeb- layer of solvent
o If the dispersion medium is separated from thedispersed phase, the sol can be reconstituted by
simply remixing with the dispersion medium.Hence, these sols are called reversible sols
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
8/46
2) Lyoph ob ic col lo ids
o Colloidal particles have very little or no attraction for the dispersion
medium ( s o lv e n t h a t i n g ) .
o Colloidal particles: in o r gan ic pa r t ic le s (e.g. gold, silver, sulfur.)Dispersion medium: w a t e r .
- These colloids are easily precipitated on the addition of smallamounts of electrolytes, by heating or by shaking
- Less stable as the particles surrounded only with a layer ofpositive or negative charge
- Once precipitated, it is not easy to reconstitute the sol bysimple mixing with the dispersion medium. Hence, these sols
are called irreversible sols.
o Not obtained simplyi.e need special method for preparation
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
9/46
2) Lyop h ob ic co l lo id s
o M e th o d s t o p r e p a r e lyo p h o b iccol loids :
A) Dispersion methods:o coarse particles are reduced in sizeby;
1) Ultrasonic generator
2) Electric arc.
3) Colloid mill.
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
10/46
1) U lt r a s o n i c ge n e r a t o r :
Dispersion achieved by high intensity UG at frequencym ore than
20,00 0 cycles/ second
2 ) Ele ct r ic a r c :
Involves production of an electric arc within the liquid anddispersion achieved byintense heat generated by the arc so somemetal of the electrodes dispersed as vapor then condense to colloidalparticles.
3) Col lo id a l m i ll:
Material shearedbetween 2 rapidly rotating close plates.
Low efficiency & reduce the size of small proportion of particlesonly.
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
11/46
2 ) Elect r ic ar c:
ice
Dispersion medium(Water + kOH)
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
12/46
B ) Co n d e n s a t io n m e t h o d s :
materials ofs ub co ll o ida l dimensions are caused to aggrega t e intoparticles with colloidal size range by;
1) Change in solvent.
2) Chemical reaction.
1) Ch a n ge in s o l ve n t :
Change in solvent Super saturation Formation &growth of nuclei.
( colloidal system formation)e.g. sulfur and alcohol inexcess of water
2) Ch em ica l r eac t ion :
Hydrogen sulfide
Br2 + H2S S + 2 HBr
HNO3 + H2S H2O + NO2 + S
Oxidatn. Sulfur atoms Sulfur sol.
Hydrolysis Ferric oxide sol. (red color).
Hydrogen sulfide + arsenous acid Double decomp. Arsenous sulfide sol.
Ferric chloride + water
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
13/46
3. Association colloids:
o Certain molecules or ions termed amphiphile
(surface active agent SAA) are characterized by two
distinct regions of opposing solution affinities within
the same molecules or ions.
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
14/46
3. Association colloids:
- At low concentration: amphiphiles existseparately (subcolloidal size)
- At high concentration: form aggregates ormicelles (50 or more monomers) (colloidal
size)
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
15/46
3. Association colloids:
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
16/46
As with lyophilic sols, formation of association colloids is
spontaneous, provided that the concentration of the
amphiphile in solution exceeds the cmc.
Amphiphiles may be
1. Anionic (e.g., Na. lauryl sulfate)
2. Cationic (e.g., cetyl triethylammonium bromide)
3. Nonionic (e.g., polyoxyethylene lauryl ether)
4. Ampholytic (zwitterionic) e.g., dimethyl dodecyl
ammonio propane sulfonate.
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
17/46
Comparison of properties of colloidal sol
Lyoph i l i c
( s o l v e n t - l o v i n g ) .
L yo p h o b i c
( s o l v e n t - h a t i n g ) .
A sso c ia t i o n (a m p h o p h i l i c ) .
Dispersed
phase
L arg e o rg a n i c
m o l e cu l e s l y i n g w i t h i n
co l lo ida l s i ze
I n o rg a n i c p a r t i c l e s
such as go ld o r
s i l ve r
Aggrega tes (m icel les) o f sma l l
o rgan ic mo lecu les o r ions
w hose s ize i s be low the
co l lo ida l s ize
So lv at io n So lv a t ed l i t t l e Hydroph i l i c o r l i poph i l i c po r t ion
o f th e mo lecu les i s so lva ted
d e p en d in g o n t h e m e d iu m
Pr e pa ra t io n Sp on t an eo us by
d isso lv ing in so lven t
Needs specia l
p ro ce d u re
Spon t aneous w hen conc. Of
a mp h i p h i l e s e xce e d s cm c
Viscosi t y Visco si t y i n cr eased as
the conc. i ncrease . A t
cer t a in conc. Gel so l
g e l f o rm a t i o n .
No t g re a t l y
increased due to
u n so l va t i o n
I ncreased as conc. Of
am ph iph i le i ncrease as
m ice l les no . i ncrease &
b e co me a symme t r i c .
Ef fect o fe l e c t ro l y t e s
Stab le in p resence o f
e lec t r o l y tes
D eso l v a t i on and s a l t i ng ou t
i n h igh c onc .
U nstab le due t o
neu t r a l i z at i on o f
c ha r ges on pa r t i c l es
Cm c i s reduced and sa l t i ng
o u t o ccu r a t h i g h sa l t co n c .
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
18/46
Sha pe o f co llo ida l par t i cles :
o The more extended theparticle, the greater itsspecific surface & the greaterthe opportunity for attraction.
o Properties of colloids as Flow,sedimentation rate & O.P. areall affected by the shape ofthe particles.
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
19/46
Pu r i fi ca t ion o f co llo ids
o 1) W h y ?
M a n y lyo p h o b ic s o ls c o n t a i n m o r e o r le s s m a t e r ia l in t r u e
s o lu t io n . wh i ch m a y b e u n d e s ir a b le fo r a n y n u m b e r o f
r easo n s ; e .g .,
n e le c t r o l yt e i m pu r i ti e s : ca u se t h e f loc cu la t i on o f t h e
sol .
2 ) H o w ?
a) Dialysis.
b) Electro dialysis.
c) Ultra filtration.
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
20/46
a) - D ia l y si s:o Depend ondifference in size between colloidal
particles & molecular particles (impurities).
o Technique;1) usesemi permeable membrane (e.g. collodion
(nitrocellulose), cellophane).
2) pore size of used semi permeable membrane preventpassage of colloidal particles & permit passage ofsmall molecules & ions (impurities) such as urea,
glucose, and sodium chloride, to pass through.o A type of dialysis equipment; Neidle dialyzer
o At equilibrium, the colloidal material is retained in
compartment A, while the subcolloidal material is
distributed equally on both sides of the membrane.
By continually removing the liquid in compartmentB, it is possible to obtain colloidal material in A
that is free from subcolloidal contaminants
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
21/46
b ) - El ect r o d i al y si s:o Technique;
o An electric potential may be used to
increase the rate of movement of ionic
impurities through a dialyzing
membrane and so provide rapid
purification.
o Electrodialysis is carried out in a three-
compartment vessel with electrodes inthe outer compartments containing
water and the sol in the center
compartment.
o A typical apparatus is shown in the figure. Application of electrical potential
causes cations to migrate to the negative electrode compartment and anions to
move to the positive electrode compartment, in both of which running water
ultimately removes the electrolyte.
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
22/46
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
23/46
Ar t i fic ia l k idn ey m ach in e :
pa t i en t s b lood ( a r t e r i a l) pass through Cellopha n e co i ls ( i dea l s em i
p e r m e a b le m e m b r a n e fo rhaem odia lys i s ) .
ce lloph an e pa s s u r ea , glu cos e , e l ect r o lyt e s bu t do n t pa s sp l a s m a p r o t e ins & b lood ce l ls
p u r e d ia l yze d b l o o d e n t e r t h e b o d y a g a in t h r o u g h a v e in .
N .B .
success of the artificial kidney m achinedepends on its ability to reduce blood urea.
Cellophane coils are supported on a drumrotat ing in electrolyte solution (rinsing
fluid).
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
24/46
Im p o r t a n ce o f t h e r in s in g s o lu t io n :
S u b s t a n c e s p r e s e n t i n exces s i n b lood (e .g. u r ea ) d i f fuse fr o m b lo o d to
t h e r i n s in g so lu t i o n .
S u b s t a n c e s w h i ch a r e de f ic ien t i n b lood (e .g. b i ca r bon a t e ) d i f fuse f rom
t h e r i n s in g s o lu t i o n t o b l o o d .
S u b s t a n c e s w h i ch a r e p r e s e n t in n o r m a l a m o u n t s in b lo o d a r e k e p t
u n a l t e r e d h a v e t h e s a m e co n c . I n b o t h b lo o d a n d r i n s in g s o lu t i o n .
Sui t a r t ificia l k idn ey m a ch in e ;
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
25/46
P h ar m aceu t ica l ap p l ica t ion s o f co llo i ds ;
1) Col lo ida l s ilver iodide , s ilver ch lor ide & s i lver p r o te in ar e
effect ive g e r m i cid e s & n o t cau s e ir r it a t i on as i on i c s ilve r s a l t s .
2 ) Co l lo ida l copp er u s ed i n cancer .
3) Co l lo ida l go ld u s ed as d i a g n o s t i c a g e n t .
4 ) Co l lo ida l m er cur y u s ed i n s y p h i l i s .
5) Asso cia t ion col lo ids (SAA) ar e u sed to i nc rease so lu b i li t y &s tab i l i t y o f c e r t a in c o m p o u n d s i n a q u e o u s & o ily
p h a r m a c eu t ic a l p r e p a r a t io n s .
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
26/46
7) B lo o d p la sm a s u b s t it u t es as de x t r a n , PVP & ge la t i n a r e
h y d r o p h ilic c o llo id s u s e d t o r e s t o r e o r m a i n t a i n b lo o d v o lu m e .
8 ) I r o n - d e x tr a n c o m p le x fo r m n o n -io n ic h y d r o p h i lic s o lsu s e d fo r t r e a t m e n t o f a n e m i a .
Su it P h a r m a c e u t ica l a p p lica t io n s o f
col lo ids ;
6 ) Ef f icien cy o f c e r t a i n s u b s t a n c e s is in c r e a s e d w h e n u s e d i n
c o llo id a l fo r m d u e t o la r g e su r fa c e a r e a .e.g. efficiency of kaolin in adsorbing toxins from GIT.e.g. efficiency of aluminum hydroxide as antacid.
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
27/46
Pr op e r t ie s o f co llo ids
A) K in e t ic p r o p e r t ie s .
B) O p t ica l p r o p e r t ie s .
C) E le c t r i ca l p r op e r t ie s .
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
28/46
A) Kin e t ic p r o p e r t ie s :
W h i ch r e la t e t o t h e m o t io n o f t h e p a r t ic le s w it h i n t h ed i sp e r s io n m e d iu m a s fo llo w in g:
Br o w n ia n m o t io n .
Diffus ion .
S e d i m e n t a t i o n .
Os m o t ic p r e s su r e .
Th e D o n n a n m e m b r a n e e ffe ct .
Viscosity.
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
29/46
1) Br o w n ia n m o t io n :
o Def in i t ion: colloidal particles are subjected torandom collision with molecules of the dispersionmedium (solvent) so each particle move in irregularand complicated zigzag pathway.
o
First observed by Robert Brown (1827) with pollengrains suspended in water.
o The ve loc i ty of pa r t i c les i n c r e a s e s wi thd e c r e a s i n g pa r t i c le s ize an d v i scos i ty.
o In c rea s in g t he v i scos it y o f d i spe r s ionm e d i u m (by g lycer in) d e c r e a s e t h e n s t o p
Br o w n i a n m o t io n .
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
30/46
2) Di ffu s ion :
o Defini t ion :o As a result of Brownian motion
particles pass (diffuse) from a region ofh i g h e r concentration to one with lo w e r
conc.
o Rate of diffusion is expressed by;
Fick s f i r s t law :dm/dt = -DA dc/dx
W h e r e d m is t h e m a s s o f s u b s t a n c ed i ffu s ing in t im e d t a cr o s s a n a r e aA u n d e r t h e in flu e n c e o f ac o n c en t r a t io n gr a d ie n t d C / d x.
Th e m in u s s ign d e n o t e s t h a t
d i ffu s ion t ak es p l ace in t h ed i r e c t io n o f d e c r e a s in gc o n c e n t r a t i o n .
D is the d i ffu s ion coef fi cien t .
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
31/46
3 ) Se d i m e n t a t i on :
o Stok es law ;
V = 2 r 2 ( p -po ) g / 9
v: ve loc i ty o f sed imen ta t ion o f sphe r ica l pa r t i c le s .
p : den s i ty o f the sph e r ica l pa r t i c le s .
p o : d e n s i t y o f t h e m e d iu m .
: v iscos i ty o f th e m ed ium .
g : accele ra t ion d ue to g ra v ity .At sm al l p ar t i cle s ize ( le s s t h a n 0 .5 u m ) B r o w n i a n m o t io n i s
s ig n i fic a n t & t e n d t o p r e ve n t s e d i m e n t a t io n d u e t o g r a v it y &
p r o m o t e m ix in g in s t ea d .
s o , w e u s e a n u l t r a c e n t r i f u g e w h ic h p r o v id e s t r o n g er f o r c e s op r o m o t e s e d im e n t a t io n i n a m e a s u r a b le m a n n e r .
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
32/46
4 ) Os m o t ic p r e s s u r e :
o Th e m e t h o d i s b a s e d o n Van ' s H of f' s law ;P = R TC / M
o F r o m t h e eq u a t io n ;
a ) Th e o s m o t ic p r e s s u r e (P ) d e p e n d s o n m o l a r c o n c . O f t h e
s o l u t e (C) & o n a b s o lu t e t em p . (T) .
b ) Th e o s m o t ic p r e s s u r e i s inver se ly p r o p o r t io n a l t om o le c u la r w e ig h t ( M) .
R= molar gas constant
o The equ a t i on is va lid fo r ve r y d il u t e s o lu t i on s in wh icht h e m o le c u le s d o n o t in t e r a c t m u t u a l ly.
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
33/46
5 ) Th e D o n n a n m e m b r a n e e ffe ct .
o Def in i t ion:
Diffu s ion o f sm a l l i ons t h r ou gh am e m b r a n e w i ll b e a f fe ct e d b y t h ep r e s e n c e o f a c h a r ge d m a c r o m o l ec u let h a t ca n t p e n e t r a t e t h e m e m b r a n edu e t o i t s s i ze .
Appl ica t ion:1) Fac ili t a t in g t he abs o r p t i on o f
i on i zab l e d r ugs f rom GIT by co -a d m in i st r a t io n o f m a c r o m o le c u le s o f s a m e ch a r ge s o m u t u a l io n i cr e p u ls io n o c cu r s e .g
c o -a d m in i st r a t io n o f a n i o n icm a c r o m o l ec u le e .g . s o d i u m c a r b o x ym eth yl ce llu lose , wi th a d i ffu s ib le
an ion e .g . po t a s s iu m ben zyl pen i ci ll into e n h a n c e d i ffu s i o n of t he l a t e ra c r o s s b o d y m e m b r a n e s .
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
34/46
6) v iscos i ty
o Def in i t ion :
o Th e r e s is t a n c e to flo w o f a s ys t e m u n d e r a na p p lie d p r e s su r e
o Viscosi ty of col loid a l low s 1- ca lcu l a t ion o f t h em o le cu la r w e igh t .
2 - P r o vid e u s e fu l in fo r m a t io n a b o u t th e sh a p e o f th e co llo ida l p a r t ic les .
o N .B .o S p h e r o c o l l o i d a l d i s pe r s ions a r e o f r e la t i ve ly lo w
viscosi ty.
o On t h e o t h e r h a n d Lin ea r co ll o ida l d i sp e r s io n s a r e o f
h igh viscos i ty .o I flin ea r co l lo ida l pa r t i c l e s coi l u p in t o sp h e r e s
Th e viscos i ty of t he s ys t em fa l ls d u e t o c h a n g in g t h e
s h a p e .
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
35/46
B) O p t ica l p r op e r t ie s :
1) Ligh t sca t te r in g (Tyn d a ll e f fec t ) .
1) U lt r a m icr o s co p e .
2 ) E le ct r o n m icr o s co p e .
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
36/46
1) Light scat ter ing (Tyn d al l effect )
o Tr u e s o lu t i ons d o n o t s c a tt e r l igh t a n da pp e a r c le a r bu t co llo ida l d i s pe r s ion sc on t a i n opa qu e pa r t i cle s t ha t do s c a tt e rligh t a n d t h u s a p p e a r t u r b id .
o Tyn d al l effect :
when a beam of light pass through a colloidal
sol, scattered light cause the sol to a p p e a r t u r b i d .
o I m por t a n c e o f ligh t s ca t t e r i ngm e a s u r e m e n t s :
1) Estimate particle size .
2) Estimate particle s h a p e .
3) Estimate particles i n t e r a c t i ons .
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
37/46
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
38/46
2 ) U lt r a m ic r o s co p e :
o P a r t ic le s a p p e a r a s s p o t s
o f l igh t aga ins t t h e da r k
b a c k gr o u n d o f th e
m i c r o s c o p e .
o U s e d in t h e t e ch n iq u e o f
m ic r o e l ec t r o p h o r e s is fo r
m e a s u r in g p a r t ic le
c h a r g e .
o Give ac tua l p i c tu r e o f t hepa r t ic le s ( u p t o 5A) .
o U s e d t o o b s e r v e t h e s iz e ,s h a p e a n d s tr u ct u r e o f
so l s .o H ig h e n e r g y e le c tr o n
b e a m s a r e u s e d . (h a v eg r e a t e r r e s o lvin g p o w e r )
o O n e d is a d v a n t a g e is ;
o n ly d r ie d s a m p l es c a n b eexam in ed . Not givein fo r m a t io n o ns o lva t i on .
3 ) E le ct r o n
m i c r o s c o p e :
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
39/46
C) E lec t r ica l p r op er t ie s :
a ) E le c tr ica l p r op e r t ie s o f in t e r fa c e s .
b ) The e le c t r i ca l d ou b l e la ye r .
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
40/46
a ) E lect r i ca l p r op e r t i e s o f in te r faces :
M o st su r fa ces a cq uir e a su r fa ce e le ct r ic ch a r ge
w h en b r o u gh t in to con ta ct w it h a n a q u eo u s
m e d iu m , th e p r in cip a l ch a r gin g m e ch a n ism s
b e in g a s fo llo w s:
1) Ion d i s so lu t ion .
2 ) I o n iza t io n .
3 ) I o n a d s o r p t io n .
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
41/46
1) Ion d isso lu t ion :
o Surface charge of colloidal particle is con t r o l led b y the charge of ionpresent in excess in the medium.
o E xa m p le s ; 1) AgN o 3 + N a I AgI + N a N o3
a) silver iodide in a solution with excess iodide Particles acquire - ve
b) Aluminum hydroxide in a solution with excess hydroxide
P o t e n t ia l d e t e r m in in g io n s : ions whose conc. determine theelectric potential at the particle surface (e.g. Ag+ , I -, H+, OH- )
charge & vice versa. if excess Ag the charge will be +ve since the conc.Of Ag and I determine the electric potential
particles acquire ve charge & vice versa.
2) Ion iza t ion
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
42/46
2) Ion iza t ion
o Surface charge of colloidal particle is controlled bytheionization of surface groupings
o E x a m p l e s ;
a)polystyrene latex has carboxylic acid group at the surface, ionize to givenegatively charged particles.
b) acidic drugs as ibuprofen & na lidixic acidacquire surface negative
charged.
c)Am ino a cids & prot ein s have carboxyl & amino groups whose ionizationdepend on the pH as follow;
-NH3-R-COO
-NH3-R-COOH
+ +
At high PH
Alkaline medium
Negatively charged
COOH COO-
Zwitter ion
Iso electric point
Zero charge
At low PH
Acidic medium
Positively charged
NH2 NH3+
NH2-R-COO
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
43/46
Su i t ion iza t ion ;
o I so e le c t r i c po i n t :
o p H at wh ich + ve c h a r g e s = -ve c h a r g e s ,
o i .e. n e t ch a r ge o f t h e a m in o a c id = z er o .
o I t is a de fin i t e pH specif ic fo r e a c h p r o t e in .
o At t h i s p H p r o t e i n is leas t so lub le & pr ec ip i t a t ed .
o Q ; H o w c a n yo u p r e cip i ta t e in s u l in ? ??
o BY ADJUSTING THEpHOF the SOLUTIONTO THE ISO ELECTRIC POINT OF INSULIN
(PH 5.2) .
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
44/46
3 ) I o n a d s o r p t io n :
o Sur face cha r ge o f co l lo ida l p a r t ic le is con t r o l led b y th e
u n e q u a l a d s o r p t i o n o f o p p o s it e ly c h a r g ed i o n s
o E x a m p l e s ;
o S u r fa c e s o f s o l in w a t e r a r e m o r e o ft e n ve c h a r g e d
tha n + ve cha r ged ? !!!
B e c a u s e ca t io n s a r e m o r e h y d r a t e d t h a n a n i o n s s o
c a t io n s r e s i d e in t h e b u lk w h ile le s s h yd r a t e d a n io n s
a d s o r b e d o n t h e s u r f a ce .
b) T he e lec t r i ca l d ou b l e laye r :
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
45/46
b) T he e lec t r i ca l d ou b l e laye r :
AgNO3 + Na I AgI +Na NO3
D e ve lo p m e n t o f a n e t c h a r ge a t t h e p a r t ic le s u r f a c e a ffe c ts t h ed i s tr ib u t io n o f io n s in t h e s u r r o u n d i n g in t e r f a cia l r e g io n ,
As a r e s u lt : c o n c e n t r a t io n o f c o u n t e r i o n s in c r e a s e a t t h es u r f a c e ,
Th u s , a n e le c tr i c a l d o u b l e la y e r e x is t s a r o u n d e a c h p a r t ic le .
E x a m p l e ;
Def in i t ion:
I-
Na+At xs NaI :
AgI
AgIAgIAgI
AgIAgI
AgI
( N.B. Vice versa if xs AgNO3 )
o S ilve r io d i d e s o l s ca n b e p r e p a r e d b y t h e r e a c t io n ,
7/31/2019 Colloidal Disp[1]_ppt [Compatibility Mode]
46/46
n AgN0 3 + Na l ---- Agl + Na N0 3
o I n t h e bu lk of AgI pa r t i cles 1 : 1 r a t io of Ag+ an d I -
o I f t h e r e a c t io n is c a r r ie d o u t w it h a n exces s s i lve r n it r a t e ,
t h e r e w ill b e m o r e Ag+ t h a n l- io n s in t h e s u r fa c e o f t h e
pa r t ic le s The pa r t ic le s wi ll t hu s be p os i t ive ly cha r ged
a n d t h e c o u n t e r i o n s s u r r o u n d in g t h e m w ill b e N 0 3 -.
o Th e c o m b i n a t i o n o f t h e p os i t ive ly cha r ged s u r fa c e a n d t h ea t m o s p h e r e o f co u n t e r io n s s u r r o u n d i n g i t is c a lle d th e
e l ect r i c do u b le laye r .
o I f t h e r e a c t io n is c a r r ie d o u t w it h a n exces s Na I , t he r e wi ll
b e m o r e l- t h a n Ag + io n s in t h e s u r fa c e o f t h e p a r t ic le s
The pa r t ic le s wi ll t hu s be n ega t ive ly ch a r ged a n d t h e
co u n t e r io n s s u r r o u n d i n g th e m w ill b e N a + .