Macro- and Microemulsions - American Chemical Society

7 Effect of Chain Length Compatibility on Monolayers, Foams, and Macro- and Microemulsions

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on January 2, 2017 | http://pubs.acs.org Publication Date: March 27, 1985 | doi: 10.1021/bk-1985-0272.ch007

M. K. SHARMA, S. Y. SHIAO, V. K. BANSAL, and D. O. SHAH Departments of Chemical Engineering and Anesthesiology, University of Florida, Gainesville, FL 32611

The effect of chain length compatibility of various surfactants on molecular packing, foams, macro- and microemulsion structures, solubilization and oil displacement efficiency in porous media has been studied using different techniques. Moreover, the solubilization of water in microemulsions was studied in detail as a function of alkyl chain length of oils and cosurfactants. The solubilization behavior is discussed in terms of partitioning of alcohol among oil, water and the interface depending upon the chain length of alcohol andoil,as well as in terms of molecular packing at the interface in relation to the disorder produced by the chain length compatibility effects. It is proposed that the chain length compatibility strikingly affects the properties of interfacial film, which in turn influences emulsion stability, foam stability, solubilization capacity, molecular packing at the interface, fluid displacement efficiency and effective gas mobility in oil recovery processes. The formation and s t a b i l i t y of foams and emulsions depend on the structure of surfactants and cosurfactants employed in these systems. It has been reported that the structure of alcohol strongly influences the properties of microemulsions (.1-.5 ) . Moreover, the i n t e r f a c i a l composition and alcohol p a r t i t i o n i n g between aqueous phase and oil are influenced by the a l k y l chain length ofoiland alcohol (6^.7). The s t r u c t u r a l aspects of microemulsions using various techniques such as X-ray d i f f r a c t i o n , viscometry, l i g h t scattering, u l t r a c e n t r i f u g a t i o n , electron microscopy and e l e c t r i cal conductivity have been reported by previous investigators (8-10). From these studies, it is proposed that microemulsions are i s o t r o p i c , clear or translucent and thermodynamically stable dispersions ofoil,water and emulsifiers with the droplet diameter ranging from 100 - 1000 Â.

0097-6156/85/0272-0087$06.00/0 © 1985 American Chemical Society

Shah; Macro- and Microemulsions ACS Symposium Series; American Chemical Society: Washington, DC, 1985.


88

M A C R O - A N D MICROEMULSIONS

S c h i c k and Fowkes (11) s t u d i e d the effect of alkyl chain length of surfactants on c r i t i c a l m i c e l l e c o n c e n t r a t i o n (CMC). The maximum l o w e r i n g o f CMC o c c u r r e d when both the anionic and nonionic surfactants had the same c h a i n length. It was a l s o r e p o r t e d t h a t the c o e f f i c i e n t o f f r i c t i o n between polymeric surfaces reaches a minimum as the c h a i n l e n g t h o f p a r a f f i n i c o i l s approached t h a t o f s t e a r i c a c i d ( 1 2 ) . In o r d e r t o delineate the effect of chain l e n g t h o f f a t t y a c i d s on l u b r i c a t i o n , the s c u f f l o a d was measured by Cameron and Crouch ( 1 3 ) . The maximum scuff l o a d was o b s e r v e d when both h y d r o c a r b o n oil and f a t t y a c i d had the same c h a i n l e n g t h . S i m i l a r r e s u l t s o f the e f f e c t o f chain length c o m p a t i b i l i t y on d i e l e c t r i c a b s o r p t i o n , s u r f a c e v i s c o s i t y and r u s t p r e v e n t i o n have been r e p o r t e d in the l i t e r a t u r e ( 1 4 - 1 6 ) . The g a s / l i q u i d and liquid/liquid systems a r e relevant to biomedical and engineering applications. The l a r g e i n t e r f a c i a l a r e a in foams, m a c r o - and m i c r o e m u l s i o n s is suitable for rapid mass transfer from gas t o l i q u i d or l i q u i d t o gas in foams and from one l i q u i d t o a n o t h e r or v i c e v e r s a in macro- and m i c r o e m u l sions. The f o r m a t i o n and s t a b i l i t y o f t h e s e systems may be i n f l u enced by the c h a i n l e n g t h c o m p a t i b i l i t y which may also influence the flow t h r o u g h porous media b e h a v i o r o f t h e s e s y s t e m s . Theref o r e , the p r e s e n t communication d e a l s w i t h the effect of chain length compatibility on the properties of m o n o l a y e r s , foams, macro- and m i c r o e m u l s i o n s . An attempt is made to correlate the chain length compatibility effects with surface properties of mixed s u r f a c t a n t s and t h e i r flow b e h a v i o r in porous media in r e l a t i o n t o enhanced oil r e c o v e r y . Experimental Materials. Sodium d o d e c y l s u l f a t e was s u p p l i e d by A l d r i c h C h e m i cal Company, Milwaukee, WI, and various alkyl a l c o h o l s were o b t a i n e d from S u p e l c o , I n c . , B e l l e f o n t e , PA, w i t h purity greater than 99%. F o r m i c r o e m u l s i o n p r e p a r a t i o n , sodium s t é a r a t e (>> 99% p u r e ) was s u p p l i e d by Matheson, Coleman and B e l l , I n c . and sodium myristate was s u p p l i e d by Κ & Κ L a b o r a t o r i e s , I n c . A l l the o i l s (>> 99% pure) were obtained from Chemical Samples Company. D o u b l e - d i s t i l l e d water was used in a l l e x p e r i m e n t s . F o r monolayer s t u d i e s , the 4 . 0 mM s o l u t i o n s o f all pure alkyl a l c o h o l s were prepared in a m i x t u r e o f m e t h a n o l , c h l o r o f o r m and n-hexane in a volume r a t i o 1 : 1 : 3 . The sand used as porous media was p u r c h a s e d from AGSCO C o r p . , Peterson, NJ. The t r a n s d u c e r used f o r the measurements o f p r e s s u r e drop a c r o s s the porous medium was s u p p l i e d by (Validyne DP15), Validyne Engineering Corporation, Northridge, CA. The r e c o r d e r was o b t a i n e d from ( H e a t h / S c h l u m b e r g e r 225), Heath Com pany, Benton Harbor, MI. The water was pumped u s i n g Cheminert M e t e r i n g Pump (Model EMP-2), Laboratory Data Control, Riviera Beach, F L .



7.

S H A R M A

ET

AL.

Effect of Chain Length Compatibility

Methods. Using an Agla microsyringe, a l k y l alcohol solution (O.025 ml) was spread on the subsolution of O.01 M HC1. A time i n t e r v a l of 5 minutes was allowed for spreading solvents to evaporate or diffuse in the subsolution from the monolayers. The monolayer was compressed at a constant rate by an e l e c t r i c a l l y operated motor. The surface pressure area curve for a monolayer was recorded automatically by x-y recorder. Three to five monolayers of each mixture were studied and the results reported are average values. The r e p r o d u c i b i l i t y of data was + O.15 Â /molecule. The detailed discussion of the apparatus is given elsewhere (17). The macroemulsions were prepared by mixing an aqueous surfactant solution and oil in a volume r a t i o 3:1. O i l phase also contained an equimolar a l k y l alcohol. The emulsions were produced by using an ultrasonic device (Model W185) for two minutes. The volumes of the emulsions were recorded at d i f f e r e n t time i n t e r vals. The microemulsions were prepared by mixing surfactant (1 g), alcohol (4 or 8 ml), oil (10 ml) and water (1 ml) to get a clear solution. The water s o l u b i l i z a t i o n capacity was determined by adding more water slowly from a graduated 1 ml pipette to the microemulsion, u n t i l t u r b i d i t y was observed and two-phase formation occurred upon standing. The surface tension of freshly prepared aqueous solutions was measured by Wilhelmy plate method (18) and surface v i s c o s i t y was measured by a single knife-edge rotational viscometer (19). For flow through porous media studies, the sandpacks used as porous media were flushed v e r t i c a l l y with carbon dioxide for an hour to replace i n t e r s t i t i a l a i r . D i s t i l l e d water was pumped and the pore volume (PV) of the porous medium was determined. By this procedure, the trapped gas bubbles in the porous media can be e a s i l y eliminated because carbon dioxide is soluble in water. For determining the absolute permeability of the porous medium, the water was pumped at various flow rates and the pressure drop across the sandpack as a function of flow rate was recorded. After the porous medium was characterized, the mixed surfactant solutions of known surface properties were injected. This was followed by a i r i n j e c t i o n to determine the e f f e c t of chain length compatibility on f l u i d displacement e f f i c i e n c y , breakthrough time and a i r mobility in porous media. Results and Discussion Mixed Monolayers. Figure 1 shows the excess area/molecule when C^g a l k y l alcohol was mixed with a l k y l alcohols of various chain lengths. In t h i s figure, A^g represents the molecular area at surface pressure of 20 dynes/cm, whereas A and A represent the area/molecule at zero surface pressure in the condensed and expanded states of the mixed monolayers. The excess area/molecule is the difference between the experimentally measured area/molecule in the mixed monolayers and that expected from the simple a d d i t i v i t y rule (17 ). The comparison of the results of area/molecule in pure and mixed monolayers indicates that the mixed a l k y l alcohols of different chain lengths form a


89

MACRO- AND MICROEMULSIONS

90


1.6 COMPRESSION RATE 6.5 A / M O L E C U L E S / M I N . 2

1.4 H

ο

1.2

I4 & lii-îii tri Figure

2.

Schematic Diagram o f the Chain Length Compatibility and the Thermal Motion o f the T e r m i n a l Segments o f Molecules.

1.6 COMPRESSION RATE 6.5A /M0LECULE/MIN. 2

COMPRESSION RATE • 2.7 A /MOLECULE/MIN.

I.4H

2

COMPRESSION RATE « 1.0 A / M O L E C U L E / M I N . 2

1.21

< 1.0

ο ( LΚ u α.

O.6

O.4H

ω

O.2

C|6

Cie

C^b

C 2

C20

C20

C20

C20

•

•

•

2

•

CHAIN LENGTH OF FATTY ALCOHOLS(lrl) Figure

3.

E f f e c t o f Compression Rate on the E x c e s s A r e a / M o l e c u l e for V a r i o u s A l k y l A l c o h o l s w i t h C ^ h L ,0H A l c o h o l as a common Component a t pH 2.O.


93


7. SHARMA ET AL.

concept of chain l e n g t h c o m p a t i b i l i t y in m o n o l a y e r s , t h i s study was f u r t h e r extended t o i n v e s t i g a t e t h e s u r f a c e chemical aspects of s e v e r a l c o l l o i d a l systems such a s foams, m a c r o - and m i c r o e m u l sions. Foams. In o r d e r t o c o r r e l a t e t h e c h a i n l e n g t h c o m p a t i b i l i t y with surface p r o p e r t i e s o f foaming s o l u t i o n s and bubble s i z e in foams, sodium i a u r y l s u l f a t e ( C ^ r W S O ^ N a ) and v a r i o u s alkyl alcohols (CgHÔH-C^H-ÔH) used in a molar r a t i o 10:1 a s mixed foam ing agents. F i g u r e 4 shows t h e p h o t o m i c r o g r a p h s o f v a r i o u s foams containing sodium I a u r y l sulfate ( 5 . 0 m M) and d i f f e r e n t a l k y l a l c o h o l s (O.5 m M) a t 15 minutes a f t e r foams were p r o d u c e d . The mixed surfactants o f e q u a l a l k y l c h a i n l e n g t h produced t h e s m a l l e s t b u b b l e s as compared t o t h e mixed s u r f a c t a n t s o f unequal c h a i n length (e.g. C, H S0,Na + C ( +i) > η = 8, 10, 14 and 16). I t is e v i d e n t that as the d i f f e r e n c e in chain length i n c r e a s e s , t h e bubble s i z e a l s o i n c r e a s e s .


w

2

e

r

e

2 5

n

H

0 H

2 r i

w

h

e

r

e

T a b l e I shows v a r i o u s s u r f a c e and m i c r o s c o p i c p r o p e r t i e s such as s u r f a c e t e n s i o n , s u r f a c e v i s c o s i t y , foaminess ( i . e . foam volume g e n e r a t e d in a g i v e n t i m e ) and bubble s i z e in foams o f t h e s u r f a c tant solutions as a function of chain length c o m p a t i b i l i t y . The r e s u l t s i n d i c a t e t h a t a minimum in s u r f a c e t e n s i o n , a maximum in surface v i s c o s i t y , a maximum in foaminess and a minimum in bubble s i z e were o b s e r v e d when b o t h t h e components o f t h e mixed surfac tant system have t h e same c h a i n l e n g t h . These r e s u l t s c l e a r l y show t h a t t h e m o l e c u l a r p a c k i n g a t a i r - w a t e r i n t e r f a c e influences surface properties o f t h e s u r f a c t a n t s o l u t i o n s , which can i n f l u ence m i c r o s c o p i c c h a r a c t e r i s t i c s o f foams. The e f f e c t o f chain l e n g t h c o m p a t i b i l i t y on m i c r o s c o p i c and s u r f a c e p r o p e r t i e s o f s u r f a c t a n t s o l u t i o n s can be e x p l a i n e d as r e p o r t e d in the previous section. Macroemulsions. F i g u r e s 5 and 6 show t h e e m u l s i o n stability for various e m u l s i o n s c o n t a i n i n g sodium a l k y l s u l f a t e s ( C ^ * ' sodium a l k y l soaps ^ ] 2 ' ^ 1 4 ^ ^ hydrophilic emulsifiers, and v a r i o u s a l k y l a l c o h o l s as t h e h y d r o p h o b i c e m u l s i f i e r s . The s t a b i l i t y o f v a r i o u s macroemulsions was measured by r e c o r d i n g the volume o f t h e u n s e p a r a t e d e m u l s i o n in a g i v e n p e r i o d o f t i m e . The volume o f t h e e m u l s i o n was maximum when both mixed e m u l s i f i e r s had t h e e q u a l c h a i n l e n g t h ( F i g u r e s 5 and 6 ) . As t h e d i f f e r e n c e in a l k y l c h a i n l e n g t h i n c r e a s e s , t h e volume o f t h e macroemulsion decreases. It clearly shows t h a t t h e s u r f a c t a n t m o l e c u l e s w i t h s i m i l a r a l k y l c h a i n l e n g t h pack t i g h t l y a t l i q u i d / l i q u i d i n t e r f a c e similar to that observed a t g a s / l i q u i d i n t e r f a c e . Moreover, the t i g h t p a c k i n g a t t h e l i q u i d / l i q u i d i n t e r f a c e seems t o reduce t h e rate o f water or oil s e p a r a t i o n from t h e macroemulsion p h a s e . These results indicate that the gas/liquid (foams) and liquid/liquid (macroemulsions) systems behave in t h e same manner in the p r e s e n c e o f mixed s u r f a c t a n t s . a

a

s

n

e

c

o

m

m

o

n

c

n

T a b l e II shows t h e e f f e c t o f c h a i n length compatibility on oil r e c o v e r y , f l u i d d i s p l a c e m e n t e f f i c i e n c y , b r e a k t h r o u g h time and e f f e c t i v e gas m o b i l i t y in porous m e d i a . For g a s / l i q u i d systems (e.g. Foams), a maximum in fluid displacement efficiency, a


94


MACRO- AND MICROEMULSIONS

Figure 4.

Photomicrographs of Various Foams Containing Sodium Lauryl Sulfate (5 mM) and Different Alkyl Alcohols (O.5 mM).



in

Diameter

(cm)

Bubble S i z e

Foam Volume 1st Min. (ml) O.21

284

9.8X10"

(s.p.)

Surface V i s c o s -

ity

25.8

0 H

3

H

24.3

10 21 0 H

O.13

310

14.5X10"

C

3

+

H

8 17

+

C

C^H^SO^Na

C

+ 0 H

O.05

480

32.0X10"

22.9

12 25 H

3

C^H^SO^Na

C

+ 0 H

O.16

298

26.2X10"

25.6

14 29 H

3

C^H^SO^Na

E f f e c t o f C h a i n Length C o m p a t i b i l i t y on S u r f a c e P r o p e r t i e s o f Mixed S u r f a c t a n t S o l u t i o n s

C^H^SO^Na

I.

Surface Tension (dynes/cm)

Surface Properties

Systems

Table

C

+ 0 H

O.17

260

21.0X10"

30.3

16 33 H

3

C^H^SO^Na


96


C S0 Na C S0 No C S0 Na C S0 Na C S0 No |2

4

|2

4

4

|2

4

|2

+

+

+

C OH

C OH

C 0H

C, 0H

e

|0

1


|2

+

13.01

|2

1

'

1

C, 0H

4

I

4

+ 6

'

'

1

1

1

1

»

C S0 Na C S0 No C S0 Na C S0 Na C S0 Na + + + + + C 0H C 0H C 0H C 0H C, 0H l4

4

|4

e

4

|4

4

|0

|4

4

|2

|4

4

|4

e

Choin-length of mixed emulsifiers

Figure

5.

Emulsion

Stability

for

the

12 25 4 ^ ^ w i t h the W a t e r - T e t r a d e c a n e R a t i o C

H

S 0

N a

m

M

a

n

d

V

a

r

i

o

u

s

(II)

Mixed A l l

C soap

C soap

C, soap

C soap

C, soap

C 0H

C 0H

C 0H

C 0H

CÔH

l2

+ e

l2

+

|0

2

+

|2

l2

+

)4

Systems

< y l A l c o h o l s (5 3:1.

of mM)

2

+

ε iao[

Initial volume of emulsions =20ml

C 3oap + C,OH |4

C $oap |4

ι C soap l4

C o OH C, OH |0

C, OH 2

(

soap

C OH M

C h a i n - l e n g t h of mixed emulsifiers

Figure

6.

C soop |4

C..OH (hi)

E m u l s i o n S t a b i l i t y f o r the Mixed Systems (4.5 mM) and V a r i o u s A l k y l A l c o h o l s ( 4 . 5 Water-Tetradecane Ratio 3:1.

o f C^Jn^Ha mM) w i t h the



II.

Effect

H 2 5

1 2

+ 2 5

0H

4

S0 Na

C H

2 5

C

1 4

H 2 5

+ 2 9

Oil

Foam

Recovery, %

Floodinq

Steam Foam

Air

Recovery, %

Surfactant

Oil

35.8

41.1

36.8

49.5

55.0

51.5

49.8

33.2

39.1

43.3

38.7

36.5

0H

4

S0 Na

C H

1 2

30.6

0H

H

46.8

2 1

1 2

41.3

+

C

25.1

1 Q

4

S0 Na

C H

1 2

Breakthrough Time ( m i n . )

C

69.6

0 H

4

S0 Na

83.0

H

2 5

8 17

H

78.1

C

1 2

77.8

C

o f C h a i n Length C o m p a t i b i l i t y on Flow Through Porous Media B e h a v i o r o f Foams and Macroemulsion Systems

Fluid Displacement E f f i c i e n c y , %

Foams

Measured Parameters

Systems

Table


C 2 5

+

3 3

35.0

47.6

35.9

27.2

0H

4

S0 Na

68.9

1 6

H

C H

1 2

98



maximum in b r e a k t h r o u g h t i m e , a minimum in e f f e c t i v e gas mobility and a maximum in oil r e c o v e r y were o b s e r v e d when b o t h the components o f mixed s u r f a c t a n t system had the same chain length. Similar results were a l s o o b s e r v e d by d i s p l a c i n g oil w i t h s o l u t i o n s of s u r f a c t a n t s of equal chain length (Table II). These results can be u t i l i z e d t o d e s i g n the s u r f a c t a n t f o r m u l a t i o n s f o r optimum performance in enhanced oil r e c o v e r y p r o c e s s e s . Microemulsions. The effect of chain length compatibility on microemulsion formation was studied by measuring the amount o f water s o l u b i l i z e d in the s y s t e m . The amount o f water solubilized as a function o f oil c h a i n l e n g t h f o r sodium s t é a r a t e system in the p r e s e n c e o f v a r i o u s a l c o h o l s is shown in F i g u r e 7. It was o b s e r v e d t h a t f o r n - b u t a n o l c o n t a i n i n g m i c r o e m u l s i o n s , the maximum amount o f water s o l u b i l i z e d d e c r e a s e d c o n t i n u o u s l y with increase in oil c h a i n l e n g t h , whereas f o r n - h e p t a n o l it i n c r e a s e d c o n t i n u ously. F o r n - p e n t a n o l and n-hexanol containing microemulsions, water solubilization reached a maximum v a l u e f o r t r i d e c a n e and dodecane s y s t e m s . S i m i l a r r e s u l t s were a l s o observed for sodium myristate system (Figure 8). A maximum in water s o l u b i l i z a t i o n was o b s e r v e d when m i c r o e m u l s i o n contains n-hexanol and decane. From the observed findings, one can c o n c l u d e t h a t when the oil chain length is increased, the solubilization capacity of microemulsions can decrease, increase or exhibit a maximum, depending upon the s t r u c t u r e and c h a i n length of alcohol used. From the r e s u l t s o f sodium s t é a r a t e and sodium m y r i s t a t e s y s t e m s , it is i n f e r r e d t h a t the water solubilization reached a maximum when a l c o h o l c h a i n l e n g t h (1 ) p l u s t h a t o f the oil (1 ) is e q u a l t o t h a t o f the s u r f a c t a n t (1 . a

Our proposed e x p l a n a t i o n f o r the maximum water s o l u b i l i z a t i o n and chain length c o m p a t i b i l i t y e f f e c t o b s e r v e d f o r p e n t a n o l and h e x a n o l c o n t a i n i n g systems is s c h e m a t i c a l l y shown in Figure 9. The size of m i c r o e m u l s i o n d r o p l e t s is e x p e c t e d t o i n c r e a s e w i t h i n c r e a s i n g water c o n t e n t which in t u r n i n c r e a s e s the interfacial area. Up t o a c e r t a i n e x t e n t , the a l c o h o l from the oil phase can p a r t i t i o n i n t o the i n t e r f a c e t o s t a b i l i z e the a d d i t i o n a l interfacial area. As the a l c o h o l in the oil phase is d e p l e t e d , f u r t h e r growth o f water d r o p l e t s would r e s u l t in an i n c r e a s e of interfacial t e n s i o n a t the oil/water i n t e r f a c e due t o an i n c r e a s e in the a r e a per m o l e c u l e . This w i l l destabilize the microemulsion as well as prevent further solubilization of water. It has been shown t h e o r e t i c a l l y (Z3) t h a t for microemulsion formation, the int^rfacial tension at the oil/water i n t e r f a c e s h o u l d be about 10 dynes/cm. When the c h a i n l e n g t h o f oil p l u s a l c o h o l is not equal to that o f the s u r f a c t a n t (1 +1 < 1 ), t h e r e w i l l be a r e g i o n o f d i s o r d e r e d h y d r o c a r b o n c h a i n s near the terminal methyl groups around the g l o b u l e s ( F i g u r e 9) due t o t h e r m a l motion which produces a disruptive effect on the packing of surfactant molecules and increases a r e a per m o l e c u l e a t the i n t e r f a c e . It was s u g g e s t e d ( Γ 7 ) t h a t the t h e r m a l motion o f a l k y l chains which causes d i s r u p t i v e e f f e c t can i n c r e a s e the i n t e r m o l e c u l a r d i s t a n c e between s u r f a c t a n t m o l e c u l e s by about O.05 A . T h i s change influ ences various properties of the systems such as e v a p o r a t i o n o f



SHARMA ET AL.

Να -STEARATE • I gm ALCOHOL* 4cc OIL- lOcc


S

5

8

10

12

14

16

CHAIN LENGTH OF OIL

Figure 7. Effect of Alcohol and O i l Chain Length on Water Solu b i l i z a t i o n Capacity of Sodium Stéarate Containing Microemulsions.

No MYRISTATE « I gm ALCOHOL • 8 cc OIL « lOcc

6

7

8

9 10

12

14

16

OIL CHAIN LENGTH

Figure 8. Effect of Alcohol and O i l Chain Length on Water Solub i l i z a t i o n Capacity of Sodium Myristate Containing Microemulsions.


100



water through m o n o l a y e r s , c o n t a c t a n g l e , s u r f a c e t e n s i o n , boundary lubrication, s u r f a c e v i s c o s i t y , bubble s i z e in foams and e m u l s i o n s t a b i l i t y o f mixed s u r f a c t a n t s y s t e m s . Therefore, our proposed e x p l a n a t i o n based on c h a i n l e n g t h s o f oil, a l c o h o l and s u r f a c t a n t , is t h a t the maximum water s o l u b i l i z a t i o n in m i c r o e m u l s i o n o c c u r r e d at 1 +1 = 1 , which is due t o the maximum c o h e s i v e i n t e r a c t i o n between h y â r o c a r b o n c h a i n s (or due t o minimum d i s r u p t i v e e f f e c t in the i n t e r f a c i a l r e g i o n ) under t h e s e c o n d i t i o n s ( F i g u r e 9 ) . F u r t h e r s t u d i e s i n d i c a t e d t h a t not o n l y the molecular packing, but also the t o t a l amount o f a l c o h o l and s u r f a c t a n t a t the interface influence the water solubilization capacity of the microemulsions (2b). As the amount o f a l c o h o l and s u r f a c t a n t a t the i n t e r f a c e i n c r e a s e s , the water solubilization capacity in microemulsions also increases. Figure 10 s c h e m a t i c a l l y i l l u s t r a t e s the proposed e x p l a n a t i o n f o r the s o l u b i l i z a t i o n b e h a v i o r o f heptanol and butanol containing microemulsions. Previous study (24) on the s u r f a c t a n t p a r t i t i o n i n g in v a r i o u s oil/water systems indicates t h a t the s u r f a c t a n t p a r t i t i o n i n g in oil phase d e c r e a s e s with i n c r e a s i n g a l k y l chain length of oil from n-hexane to nhexadecane. S i m i l a r t r e n d is a l s o e x p e c t e d f o r n - h e p t a n o l . Since the s o l u b i l i t y o f n - h e p t a n o l in water is n e g l i g i b l e , the decrease in n - h e p t a n o l p a r t i t i o n i n g in oil phase as the c h a i n l e n g t h o f oil is i n c r e a s e d from t o C^, would r e s u l t in an increase in the heptanol concentration at the interface ( e . g . i n c r e a s e in the a l c o h o l / s o a p molar r a t i o at the interface, Figure 10). This indeed was confirmed by the titration method ( F i g u r e 11) as d e s c r i b e d by Bowcott and Schulman (24.). As the chain length of oil is i n c r e a s e d , the i n t e r c e p t , which r e p r e s e n t s the molar r a t i o o f a l c o h o l t o soap a t the i n t e r f a c e , i n c r e a s e s . For m i c r o e m u l s i o n systems c o n t a i n i n g b u t a n o l , the s o l u b i l i z a tion c a p a c i t y d e c r e a s e d w i t h i n c r e a s i n g oil c h a i n l e n g t h ( F i g u r e s 7 and 8 ) . Our proposed e x p l a n a t i o n for this observation is schematically shown in Figure 10. As the oil c h a i n l e n g t h is i n c r e a s e d , a d e c r e a s e in b u t a n o l p a r t i t i o n i n g o c c u r s in the oil phase. S i n c e the t o t a l amount o f b u t a n o l is c o n s t a n t in each s y s tem, a c o n c o m i t a n t i n c r e a s e in the b u t a n o l concentration in the water phase and at the i n t e r f a c e o c c u r s . Unlike heptanol c o n t a i n i n g m i c r o e m u l s i o n s , the water p o o l in b u t a n o l systems gradually becomes water plus butanol p o o l as the b u t a n o l has s u b s t a n t i a l s o l u b i l i t y in w a t e r . T h e r e f o r e , the water p l u s b u t a n o l p o o l as a s o l v e n t w i l l s o l u b i l i z e some o f the soap m o l e c u l e s in the p o o l and remove them g r a d u a l l y from the interface, which results in a decrease in the t o t a l i n t e r f a c i a l a r e a and hence the c o n c o m i t a n t d e c r e a s e in the c a p a c i t y o f water s o l u b i l i z a t i o n . This study s u g gests that the maximum water s o l u b i l i z a t i o n o c c u r s when the soap and a l c o h o l m o l e c u l e s remain p r e d o m i n a n t l y adsorbed a t the interface as w e l l as when the c h a i n l e n g t h o f oil p l u s a l c o h o l e q u a l s t o t h a t o f the s u r f a c t a n t .



DISORDERED

F i g u r e 9.

101


7. SH ARM A ET AL.

DISORDERED

Schematic Diagram of the D i s o r d e r i n g o f the Terminal Segment o f A l k y l C h a i n P r o t r u d i n g out o f the I n t e r f a cial Film and the Solubilization Capacity of Microemulsions 1 , 1 and 1 a r e the C h a i n L e n g t h s o f A l c o h o l , O i l and § u r f a c t a n t Rolecules, r e s p e c t i v e l y .

HEPTANOL CONTAINING MICROEMULSIONS C OIL

C OIL

8

12

A

BUTANOL

Β Increase In Interfacial Area CONTAINING MICROEMULSIONS

|3rvUW. eo«L c

^ U A ^ C

1

2

O . L

C

WATER + HEPTANOL

fc

ÛU^

0 1 6

OIL

WATER D~

E

F

Decrease In Interfacial Area ^

F i g u r e 10.

Schematic I l l u s t r a t i o n o f the E f f e c t Chain Length on the Partitioning Water, O i l and I n t e r f a c i a l R e g i o n .

of Increasing o f A l c o h o l in


Oil the



102

Figure 11.

E f f e c t of O i l Chain Length on the tion Plots for Microemulsions.

Oil/Alcohol


Titra-

7.

SHARMA ET AL.


103

Literature Cited 1. 2. 3.


4. 5.

6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25.

Cooke, C. E.; Schulman, J. H. in "Surface Chemistry"; Ekwall, P; Groth, K.; Runnstrom-Reio; Eds.; Academic Press, New York, 1965, pp. 231-251. Frank, S. G.; Zografi, G. J. Colloid Interface Sci. 1965; 29, 28. Sjoblom, E.; Friberg, S. J. Colloid Interface Sci. 1978, 67, 16. Higuchi, W. I.; Misra, J. J. Pharm. Sci. 1962, 51, 455. Shah, D. O.; Walker, R. D. Jr.; Hsieh, W. C.; Shah, H. J.; Dwivedi, S.; Nelander, J.; Pepinsky, R.; Dermer, D. W., SPE Paper 5815 presented at Improved Oil Recovery Symposium of SPE of AIME, Tulsa, OK. 1976, March 22-24. Bansal, V. K.; Chinnaswamy, K; Ramachandran, C.; Shah, D. O., J. Colloid Interface Sci. 1979, 72, 524-537. Chan, K. S.; Shah, D. O. J. Dispersion Sci. Technol. 1980, 1, 55-95. Stoeckenius, W.; Schulman, J. H.; Prince, L. M. Kolloid-Z. 1960, 169, 170. Schulman, J. H.; Riley, D. P. J. Colloid Sci. 1948, 3, 383. Schulman, J. H.; Stoeckenius, W.; Prince, L. M. J. Phys. Chem. 1959, 63, 1677. Schick, M. J.; Fowkes, F. M. J. Phys. Chem. 1957, 61, 1062. Fort, T., Jr., J. Phys. Chem. 1962, 66, 1136. Cameron, Α.; Crouch, R. F., Nature 1963, 198, 475. Meakins, R. J., Chem. Ind. 1968, 1768. Ries, Η. Ε., Jr.; Gabor, J., Chem. Ind. 1967, 1561. Sharma, M. K.; Shah, D. O., Proc. 18th Intersociety Energy Conversion Engineering Conference, 1983, August 21-26, 527534. Shiao, S. Y., Ph.D. Thesis, University of Florida, Gaines ville, FL., 1976. Wilhelmy, L., Ann. Physik 1863, 119, 117. Brown, A. G.; Thuman, W. C.; McBain, J. W., J. Colloid Sci. 1953, 8, 491. Shah, D. O.; Schulman, J. H., J. Lipid Res. 1967, 8, 215. Shah, D. O.; Schulman, J. H., J. Lipid Res. 1967, 8, 227. Shah, D. O.; Schulman, J. H., J. Colloid Interface Sci. 1967, 25, 107. Ruckenstein, E. in "Micellization, Solubilization and Micro emulsions," K. L. Mittal, ed.; Plenum Press, New York, 1977, Volume 2, pp. 755-778. Bowcott, J. E. L.; Schulman, J. Η., Z. Electrochem. 1955, 58, 283. Pithapurwala, Y. K., Ph.D. Thesis, University of Florida, Gainesville, FL, 1984.

RECEIVED December 20, 1984


Macro- and Microemulsions - American Chemical Society

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