Coacervate formation by aerosol OT with sodium chloride

Coacervate Formation by Aerosol OT with Sodium Chloride was d e t e r m i n e d b y u l t r a v i o l e t absorbance at a w a v e l e n g t h of 215 rim. I n a n o t h e r series, the salt c o n c e n t r a t i o n was k e p t c o n s t a n t at 2.5% in all t h e systems. Aerosol OT c o n c e n t r a t i o n s were v a r i e d from 1 to 10% (w/v). T h e volumes of the upper a n d lower phases were m e a s u r e d after the systems reached a n e q u i l i b r i u m state. T a b l e I summarizes the general characteristics and volumes of coacerv a t e phases as a f u n c t i o n of sodium chloride conc e n t r a t i o n in t h e range of 1 to 4%. T h e r e is no phase s e p a r a t i o n u n t i l a p p r o x i m a t e l y 1.6% salt c o n c e n t r a t i o n is reached. F u r t h e r increase in salt

T h e b i n a r y and t e r n a r y phase equilibria diagrams of sodium di(2-ethylhexyl) sulfosuceinate [Aerosol OT], h y d r o c a r b o n s a n d w a t e r systems h a v e b e e n discussed in detail b y Ekwall, M a n d e l l , a n d F o n t e l l (1, 2). However, no previous report has b e e n m a d e concerning t h e ability of Aerosol OT to form coacervates and of t h e theological properties of these coacervates. I t is t h e purpose of this p a p e r

TABLE

I

PROPERTIES OF AEROSOL O T

Salt conch

(%)

1-1.6

Vol of lower phase (ml)

COACERVATESa Appearance

Conchof Aerosol OT in the lower phase (%)

.....,,.,,.,,.,,,,, Upper phase

4O

Lower

phase 30

No phase s e p a r a t i o n

1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4

94.60 79.00 66.00 42.00 40.00 41.00 40.50 38.00 37.00

3.6 3.8 4.0

34.50 30.00 29.00

10.21 11.37 13.41 20.43 23.68 23.64 24.05 25.32 25.80 B e g i n n i n g of precipitation (i.e., a t h i r d , phase)

Turbid Turbid Clear Clear Clear Clear Clear Clear Clear

Clear Clear Clear Clear Clear Clear Clear Clear Clear

Clear Clear Clear

Cloudy or ppt.

-S > 20

10

[

l

I

I

r

[

I

I

[

i

2

5

4

5

6

7

8

9

1O

II

[2

% Conc. of Aerosol-0T(W/V)

F I G . 1. P e r c e n t volume coacervate phase as a f u n c t i o n of aerosol OT concentration.

c o n c e n t r a t i o n increases t h e c o n c e n t r a t i o n of Aerosol OT in the coacervate phase. At a salt concent r a t i o n greater t h a n 2.6% c o n c e n t r a t i o n there is no f u r t h e r increase of Aerosol OT in the eoaeervate phase. Figure 1 shows t h e percentage b y volume of the eoaeervate phase as a f u n c t i o n of Aerosol OT c o n c e n t r a t i o n in t h e systems which all cont a i n e d a 2.5% c o n c e n t r a t i o n of salt. T h e volume of t h e coacervate phase increases w i t h the increase in Aerosol OT concentration. Aqueous dispersions of Aerosol OT in concent r a t i o n s of 5% or higher were found to exhibit c h a r a c t e r i s t i c aging properties. After aging a t room t e m p e r a t u r e for a period of 2 weeks or more, mild s h a k i n g converts t h e liquid into a gel s t r u t -

I

100 ml of 10% (w/v) Aerosol OT in all systems.

to m a k e a p r e l i m i n a r y r e p o r t on findings on t h e physical properties of Aerosol OT, sodium chloride a n d w a t e r coaeervate systems. T h e required q u a n t i t i e s of sodium chloride were added to dispersions of Aerosol OT in distilled water. W i t h i n a few m i n u t e s oil-like droplets beg a n to s e p a r a t e a n d settle. T h e phase s e p a r a t i o n was allowed to proceed u n t i l t h e r e was no f u r t h e r change in t h e volumes of the two liquid phases. T h e c o n c e n t r a t i o n of Aerosol OT in each phase Copyright © 1972 by Academic Press, Inc.

I

1

Journal of Colloid and Interface Science, Vol. 40, No. 1, July 1972.

125

126

LETTERS TO.TttE EDITORS

ture. The gel structure reverts to the liquid state within 15 to 20 rain after cessation of shearing. A more detailed report on the nature of the coacervate phase and its rheoplexotropic properties will be published later. REFERENCES

1. ]~I(-WALL, ~., ~/[2~NDELL~ L., AND FONT]ELL, I~., J. Colloid Interface Sei. 33, 215 (1970). 2. PAn~, D., ROGERS, J., TOFT, ]=~. W., AND

Journal of Colloidand InterfaceScience,Vol. 40, No. 1, July 1972

WINSOR, P. A., J. Colloid Interface (1970). ~. B. R.

Sci. 32, 81 ACHARYA ECANOW BALAGOT

University of Illinois, College of Pharmacy Chicago, Illinois 60612; and Hines V.A. Hospital, H~ines, Illinois 60141 Received January 11, I972; accepted April 7, I972