Characterization of Inverted Micelles of Calcium Alkarylsulfonates by

7 Characterization of Inverted Micelles of Calcium Alkarylsulfonates by Some Pyrene Fluorescence Probes Tze-Chi Jao and Kenneth L. Kreuz

Downloaded by HARVARD UNIV on June 17, 2014 | http://pubs.acs.org Publication Date: June 5, 1986 | doi: 10.1021/bk-1986-0311.ch007

Texaco Research Center, Beacon, NY 12508

1-Pyrene carboxaldehyde and a series of pyrene carboxylic acids were found useful as fluorescence probes in describing the constitution of inverted micelles of certain calcium alkarylsulfonates in hydrocarbon media. 1-Pyrene carboxaldehyde is a convenient probe for studying the particle sizes of micelles in the region of 100A. A series of graded probes, pyrene carboxylic acids with varying alkyl chain length, have been used to determine internal fluidity and micropolarity as a function of distance from the polar core of these inverted micelles. Pyrene excimer to monomer fluorescence intensity ratio and fluorescene lifetime provided the means of measurement of internal fluidity and micropolarity, respectively.

The use of the fluorescence probe as a tool for characterizing aggregate systems in non-polar media (e.g.; "inverted micelles") has become increasingly popular within the last decade among chemists and biochemists (1-4). Its utility has been demonstrated for providing constitutional (e.g.; micro-viscosity, -polarity, and -pH) information on aggregates, and for demonstrating the dynamic nature of these structures. Such information has been applied toward an improved understanding of the function of bio-membranes, and to a better utilization of surfactants in industrial processes and products. Much remains to be learned, however, regarding the limits of applicability of the fluorescence probe technique to aggregates in non-polar media. A number of obvious experiments are conspicuous by their absence from the published literature. For example, 1-pyrene carboxaldehyde is a well known probe which has been used to measure the microscopic polarity of sodium dodecyl sulfate micelles in aqueous medium (5); there is, however, no account of its use in non-polar media. 0097-6156/ 86/ 0311 -0090S06.00/ 0 © 1986 American Chemical Society

In Phenomena in Mixed Surfactant Systems; Scamehorn, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

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The p r e s e n t s t u d y demonstrates the u t i l i t y o f the above probe i n d e s c r i b i n g the c o n s t i t u t i o n of aggregates of c e r t a i n a l k a r y l s u l f o n a t e s i n h y d r o c a r b o n media. I t a l s o demonstrates t h e use o f the probe t e c h n i q u e i n measuring the m i c r o p o l a r i t y o f t h e s e same a g g r e g a t e s as a f u n c t i o n o f d i s t a n c e from t h e p o l a r c o r e . The m i c r o v i s c o s i t y o f i n v e r t e d o r normal m i c e l l e s i n t h e p a s t has been e s t i m a t e d o n l y as an average v a l u e o f e i t h e r t h e p o l a r o r n o n - p o l a r regions ( 6 ) . I t i s worthy o f note t h a t t h e m i c e l l a r systems d e a l t w i t h i n t h i s s t u d y d i f f e r from c o n v e n t i o n a l " i n v e r t e d m i c e l l e s " i n t h a t they contain s o l u b i l i z e d inorganic species i n t h e i r cores. I t was o f a d d i t i o n a l i n t e r e s t t o o b s e r v e t h e response o f such systems t o the f l u o r e s c e n c e probe t e c h n i q u e .


Experimental Materials. 1-pyrene c a r b o x a l d e h y d e , 1-pyrene v a l e r i c a c i d (PVA), 1-pyrene n o n a n o i c a c i d (PNA), and 1-pyrene h e x a d e c a n o i c a c i d (PHA) were purchased from M o l e c u l a r Probes, I n c . (Eugene, Oregon). S p e c t r a l grade n-hexane, n-heptane, η-octane and n-nonane were obtained either from Burdick and Jackson Laboratories, Inc. (Muskegan, M i c h i g a n ) o r from P f a l t z and Bauer, I n c . (Stamford, Connecticut). Two k i n d s o f c a l c i u m a l k a r y l s u l f o n a t e s were used: s u l f o n a t e A c o n t a i n e d b a s i c Ca e q u i v a l e n t t o o n e - h a l f mole CaiOH)^ per mole o f Ca a l k a r y l s u l f o n a t e ; s u l f o n a t e Β c o n t a i n e d 20 mole o f a m i x t u r e o f CaCO^ and t h e above type o f b a s i c Ca. The average m o l e c u l a r weight o f t h e p a r e n t s u l f o n i c a c i d f o r b o t h m a t e r i a l s was 450. Both s u l f o n a t e s were a m i x t u r e o f 35% (w/w) s y n t h e t i c s u l f o n a t e ( c o n t a i n i n g o v e r 90% d i - d o d e c y l benzene s u l f o n a t e ) and 65% (w/w) petroleum sulfonate (branched monoalkaryl sulfonate ca. ^28 35^ " s u l f o n a t e s were t h e s u b j e c t o f a p r e v i o u s communication from t h i s l a b o r a t o r y (7) · A e r o s o l OT was purchased from P f a l t z and Bauer, I n c . F u r t h e r p u r i f i c a t i o n was c a r r i e d out by p r e c i p i t a t i o n from methanol; the p r e c i p i t a t e was then d r i e d under vacuum a t 40°C f o r s e v e r a l days. A l l t e s t s o l u t i o n s , e x c e p t o t h e r w i s e mentioned, were degassed by ^ h r e e freeze-pump-thaw c y c l e s w i t h a vacuum l i n e o p e r a t e d under 10 t o r r p r e s s u r e . Problems o f background f l u o r e s c e n c e o r i g i n a t i n g from s u l f o n a t e s themselves c o u l d be a d e q u a t e l y m i n i m i z e d by p r o p e r choice of probe/sulfonate r a t i o s . The e x c i t a t i o n wavelength was s e t a t 340 nm. E m i s s i o n s p e c t r a were o b t a i n e d i n c o n s t a n t energy mode. The s p e c t r a l r e s o l u t i o n was 3 nm. T

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Instrumentation. The steady-state fluorescence spectra were measured w i t h P e r k i n - E l m e r MPF-44B f l u o r e s c e n c e s p e c t r o p h o t o m e t e r . The single-photon counting instrument f o r fluorescence lifetime measurements was assembled in-house from components o b t a i n e d from EG&G ORTEC. A PRA-510B l i g h t p u i s e r f i l l e d w i t h KL gas was used as the e x c i t a t i o n s o u r c e . Instrument r e s p o n s e f u n c t i o n was o b t a i n e d w i t h DuPont Ludox s c a t t e r s o l u t i o n a t the e x c i t a t i o n w a v e l e n g t h .


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Results


1-Pyrene Carboxaldehyde Probe S t u d i e s . Fluorescence spectra of 1-pyrene c a r b o x a l d e h y d e i n nonane s o l u t i o n s o f s u l f o n a t e s A and Β and i n an o c t a n e s o l u t i o n o f A e r o s o l OT a r e compared t o the probe s p e c t r a i n pure h y d r o c a r b o n media i n F i g u r e 1. P a r t s (a) and (b) a r e o f s u l f o n a t e s A and Β systems, r e s p e c t i v e l y ; p a r t (c) i s of a e r o s o l OT system. They were c o n s t r u c t e d at d i f f e r e n t g a i n s e t t i n g s and t h e r e f o r e the i n t e n s i t i e s shown f o r the i n d i v i d u a l system a r e not d i r e c t l y comparable. The f l u o r e s c e n c e i n t e n s i t y o f 1-pyrene c a r b o x a l d e h y d e i n nonane a l o n e i s much weaker than i n e i t h e r the s u l f o n a t e A or s u l f o n a t e Β s o l u t i o n . A e r o s o l OT c o n t a i n i n g s o l u b i l i z e d H«0 does n o t enhance the f l u o r e s c e n c e i n t e n s i t y o f 1-pyrene c a r b o x a l d e h y d e as much as s u l f o n a t e s A and B, but the band maximum i s s h i f t e d as e x p e c t e d f o r t h i s probe i n a w a t e r - r i c h medium. We measured the time-dependent a n i s o t r o p y o f 1-pyrene c a r b o x aldehyde i n s u l f o n a t e A and Β systems. The r e s u l t s a r e shown i n F i g u r e 2. R e l a x a t i o n times d e t e r m i n e d from the u n c o n v o l u t e d a n i s o t r o p y decays f o r s u l f o n a t e s A and Β i n heptane s o l u t i o n were found t o be 7 ns and 28 ns, r e s p e c t i v e l y . In o r d e r to t e s t f u r t h e r the a p p l i c a b i l i t y o f 1-pyrene c a r b o x a l d e h y d e as a f l u o r e s c e n t p r o b e , we a p p l i e d Keh and V a l e u r s method (4) t o determine average m i c e l l a r s i z e s o f s u l f o n a t e A and Β micelles. T h i s method i s based on the assumption t h a t the m o t i o n o f a probe m o l e c u l e i s c o u p l e d t o t h a t o f the m i c e l l e , and t h a t the m i c e l l a r hydrodynamic volumes are the same i n two a p o l a r s o l v e n t s o f different viscosities. For our p u r p o s e s , time averaged a n i s o t r o p i e s of these systems were measured i n two n - a l k a n e s : hexane and nonane. The f l u o r e s c e n c e l i f e t i m e o f 1-pyrene c a r b o x a l d e h y d e w i t h the two s u l f o n a t e s i n b o t h these s o l v e n t s was found to be a p p r o x i m a t e l y 5 ns. The m i c e l l a r s i z e s ( d i a m e t e r ) c a l c u l a t e d f o r s u l f o n a t e s A and Β were 53 ± 5A and 82 ± 10A, respectively. S i n c e these m i c e l l e s p o s s e s e d s o l i d p o l a r c o r e s , they were p r o b a b l y more t i g h t l y bound than t y p i c a l i n v e r t e d m i c e l l e s such as those o f a e r o s o l OT. Hence, i t was e x p e c t e d t h a t the probe m o l e c u l e s would not p e r t u r b the m i c e l l e s to an e x t e n t which would s u b s t a n t i a l l y a f f e c t the m i c e l l a r s i z e s measured. I f one assumes f o r an extreme case t h a t the c o r e m a t e r i a l s o f s u l f o n a t e s A and Β a r e C a ( 0 H ) and CaCO p l u s C a ( 0 H ) respectively, one can d e r i v e a l i m i t i n g c o n s t i t u t i o n f o r these m i c e l l e s . I f one f u r t h e r assumes t h a t the d e n s i t i e s o f c a l c i u m h y d r o x i d e and c a l c i u m c a r b o n a t e i n the p o l a r c o r e a r e 2.2 g/cm and 2.4 g/cm , r e s p e c t i v e l y , and t h a t the average d e n s i t y o f b o t h m i c e l l e types e x c l u d i n g the p o l a r core i s about 1 g/cm , one a r r i v e s a t a g g r e g a t i o n numbers, c a l c u l a t e d from the m i c e l l a r s i z e s d e t e r m i n e d , f o r these two s u l f o nate m i c e l l e s to be n e a r l y the same, a p p r o x i m a t e l y 50. 1

2

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L a t e r a l M o b i l i t y ( F l u i d i t y ) o f S u l f o n a t e A and Β M i c e l l e s . The r a t i o o f excimer t o monomer f l u o r e s c e n c e i n t e n s i t y o f pyrene had p r e v i o u s l y been used to measure the f l u i d i t y o f b i o l o g i c a l membranes (8). The ease o f excimer f o r m a t i o n was c o r r e l a t e d w i t h the f l u i d i t y o f the membrane. The same p r i n c i p l e may be a p p l i e d t o the measure ment o f f l u i d i t y i n i n v e r t e d m i c e l l e s . To t h i s end, we used t h r e e pyrene c a r b o x y l i c a c i d probes o f v a r y i n g c h a i n l e n g t h : PVA, PNA and


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M

440

410 λ , nm

380

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410 λ , nm

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F i g u r e 1. F l u o r e s c e n c e spectra o f 1-pyrene c a r b o x a l d e h y d e (2.5 χ 10 M) i n : (a) s u l f o n a t e A (5.0 χ 10 M)/ nonane solution, heptane, (b) s u l f o n a t e Β (5.0 χ 10 M)/ nonane s o l u t i o n , heptane, (c) 3% (w/w) A0T/1.5% (w/w) H«0/0ctane s o l u t i o n , Octane. E x c i t a t i o n wavelength i s 350 nm.


PHENOMENA IN MIXED SURFACTANT SYSTEMS

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F i g u r e 2. U n c o n v o l u t e d a n i s o t r o p y decays o f 1-pyrene c a r b o x aldehyde i n s u l f o n a t e m i c e l l e s : (a) s u l f o n a t e A (5 χ 10 M)/ heptane (7 n s ) , (b) S u l f o n a t e Β (5 χ 10 M^/heptane (28 n s ) . The cmc o f s u l f o n a t e A i s l e s s than 10~ M, w h i l e t h a t o f sulfonate Β i s " i n f i n i t e l y " dilute.



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PHA. The r e l a t i v e l o c a t i o n o f each probe i n the m i c e l l e had r e a s o n a b l y been e s t a b l i s h e d i n our e a r l i e r r e p o r t 07) by d e m o n s t r a t i n g the a n c h o r i n g of the c a r b o x y l a t e m o i e t y i n the p o l a r c o r e . For t h i s s t u d y , we m a i n t a i n e d the pyrene probe c o n c e n t r a t i o n s c o n s t a n t , w h i l e we varied sulfonate concentration. The measured excimer to monomer r a t i o s as a f u n c t i o n o f the molar r a t i o o f probe to s u l f o n a t e f o r s u l f o n a t e s A and Β are shown i n F i g u r e 3. I t can be seen t h a t the excimer t o monomer f l u o r e s c e n c e i n t e n s i t y r a t i o s f o r the same molar r a t i o o f probe to s u l f o n a t e are much s m a l l e r i n the s u l f o n a t e A system than i n the s u l f o n a t e Β system. For b o t h s u l f o n a t e s A and B, the i n t e n s i t y r a t i o tends t o i n c r e a s e w i t h the c h a i n l e n g t h o f the c a r b o x y l i c a c i d . The v a r i a t i o n i s d i s t i n c t l y e s t a b l i s h e d f o r s u l f o n a t e Β m i c e l l e s , but l e s s so f o r sulfonate A micelles. The r e s u l t s i n d i c a t e that the internal f l u i d i t y o f the m i c e l l e s d e c r e a s e s from the edge o f the p o l a r c o r e to the c o n t i n u o u s h y d r o c a r b o n medium; the g r a d i e n t i s s t e e p e r f o r s u l f o n a t e B. P o l a r i t y V a r i a t i o n i n Sulfonate M i c e l l e s . Other workers have established a c o r r e l a t i o n between the fluorescence lifetime of pyrene i n s o l u t i o n and the p o l a r i t y o f the s o l v e n t medium (9). P o l a r media quench the e x c i t e d e l e c t r o n i c s t a t e of pyrene and hence shorten i t s fluorescence l i f e t i m e . We a p p l i e d t h i s p r i n c i p l e to measure the p o l a r i t y v a r i a t i o n w i t h i n the m i c e l l e s o f s u l f o n a t e s A and B. The f l u o r e s c e n c e l i f e t i m e s of the t h r e e pyrene c a r b o x y l i c a c i d probes (PVA, PNA, PHA) were d e t e r m i n e d w i t h o u t c o n v o l u t i o n with r e s p e c t to the i n s t r u m e n t r e s p o n s e f u n c t i o n , s i n c e the f l u o r e s c e n c e l i f e t i m e s o f the pyrene p r o b e s (280 ns) are sufficiently long compared w i t h the pulse-width of the ^ lamp p r o f i l e (5 ns). Background f l u o r e s c e n c e from the a r o m a t i c m o i e t i e s o f the s u l f o n a t e s was found to be s u f f i c i e n t l y s t r o n g t o g i v e the appearance of a double e x p o n e n t i a l (see F i g u r e 4 ) . The s h o r t e r component l a r g e l y originated from the sulfonate itself. We analyzed the longer l i f e t i m e component i n o r d e r t o c a l c u l a t e the f l u o r e s c e n c e l i f e t i m e f o r p y r e n e . The r e s u l t s are shown i n F i g u r e 5. Fluorescence l i f e t i m e s o f PVA, PNA and PHA i n heptane a l o n e were found t o v a r y s l i g h t l y among t h e m s e l v e s . S i n c e i t would not a f f e c t our i n t e r p r e t a t i o n , no attempt was made to s t u d y the o r i g i n of the d i s c r e p a n c y . I t was c o n c l u d e d t h a t the probe (PVA) t h a t i s c l o s e s t to the p o l a r c o r e o f the m i c e l l e e x p e r i e n c e s the most p o l a r environment, s i n c e i t s f l u o r e s c e n c e l i f e t i m e was found to be s h o r t e r than those of PNA and PHA. The v a r i a t i o n i n p o l a r i t y i s seen t o be g r e a t e r i n the m i c e l l e s of s u l f o n a t e A than those of s u l f o n a t e B. Discussion 1-Pyrene Carboxaldehyde i n C a l c i u m A l k a r y l s u l f o n a t e s . Our work shows t h a t 1-pyrene c a r b o x a l d e h y d e as a f l u o r e s c e n t probe f o r the s u l f o n a t e systems behaves v e r y much the same as rhodamine Β (1) and a n i l i n o n a p h t h a l e n e s u l f o n a t e ( 2 ) , whose f l u o r e s c e n c e i n t e n s i t i e s i n h y d r o c a r b o n media are enhanced i n the p r e s e n c e of i n v e r t e d m i c e l l e s . However, the i n t e n s i t y i n c r e a s e o b s e r v e d w i t h AOT was considerably l e s s than t h a t o b s e r v e d w i t h the s u l f o n a t e s . I t i s speculated that


P H E N O M E N A IN M I X E D S U R F A C T A N T

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F i g u r e 3. P l o t s o f excimer ( a t 470 nm) t o monomer (370 nm) intensity ratios as a f u n c t i o n of probe/sulfonate molar ratio. (a) s u l f o n a t e A /heptane, (b) s u l f o n a t e B / t i t a n e . T h e c o n c e n t r a t i o n s o f PHA, PNA, and PVA a r e 1 χ 10" M, 1 χ 10 M, and 5 χ 10 M, r e s p e c t i v e l y . 5

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F i g u r e 4. F l u o r e s c e n c e decay o f PVA i n t h e s u l f o n a t e A/heptane system. Wavelength o f e x c i t a t i o n i s 340 nm and e m i s s i o n i s c o l l e c t e d a t 390 nm.


Inverted Micelles of Calcium

Alkarylsulfonates


JAO AND KREUZ

F i g u r e 5 . P l o t s of the f l u o r e s c e n c e l i f e t i m e o f pyrene as f u n c t i o n o f d i s t a n c e from t h e p o l a r c o r e o f t h e m i c e l l e s s u l f o n a t e s A and Β i n heptane s o l u t i o n s .


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P H E N O M E N A IN M I X E D S U R F A C T A N T S Y S T E M S


i n the case o f s u l f o n a t e system, 1-pyrene c a r b o x a l d e h y d e c o u l d r e a c t w i t h the b a s i c s p e c i e s i n the p o l a r c o r e , so t h a t the probe c o u l d be f i r m l y h e l d by the m i c e l l e . A e r o s o l OT, o f c o u r s e , l a c k s such b a s i c m a t e r i a l s , and i n c o n t r a s t t o the s u l f o n a t e s i s a c t u a l l y a w a t e r i n - o i l microemulsion. The i n t e r n a l r o t a t i o n a l r e l a x a t i o n times o f 1-pyrene c a r b o x a l d e h y d e i n s u l f o n a t e systems may o f f e r some i n d i c a t i o n o f the e x t e n t of probe b i n d i n g t o the i n v e r t e d m i c e l l e . In the absence of any background fluorescence interference to the time-dependent a n i s o t r o p y decay p r o f i l e , the i n t e r n a l r o t a t i o n a l r e l a x a t i o n time should c o r r e l a t e with the strength of binding with the polar m a t e r i a l i n the p o l a r c o r e . However, s p e c t r a l i n t e r f e r e n c e from the a r o m a t i c m o i e t i e s o f s u l f o n a t e s i s s u b s t a n t i a l , so t h a t the v a l u e s of i n t e r n a l r o t a t i o n a l r e l a x a t i o n time can o n l y be used f o r q u a l i t a t i v e comparison. Lateral Mobility in Alkarylsulfonate Micelles. In o r d e r t o make a valid comparison o f fluidity between s u l f o n a t e s A and B, the m i c e l l a r s i z e s s h o u l d be comparable. T h i s c o n d i t i o n i s r e q u i r e d so t h a t e q u a l p o p u l a t i o n o f pyrene m o i e t i e s between the two sulfonate systems can be assumed. A l t e r n a t i v e l y , the r e q u i r e m e n t s might be met i f they have e q u a l a g g r e g a t i o n numbers. I f the above-mentioned (See S e c t i o n A under " R e s u l t s " ) assumptions r e g a r d i n g p o l a r core c o m p o s i t i o n are r e a s o n a b l e , the c o n d i t i o n f o r e q u a l probe p o p u l a t i o n between the two sulfonate micelles can still be reasonably approximated. The l a t e r a l m o b i l i t y e x p e r i m e n t s demonstrate t h a t the m i c e l l a r a g g r e g a t e , e x c l u d i n g p o l a r c o r e , of s u l f o n a t e A i s l e s s f l u i d than t h a t o f s u l f o n a t e B. I t would then f o l l o w t h a t the sulfonate m o i e t i e s are l e s s d e n s e l y packed on the p o l a r c o r e of s u l f o n a t e B. P o l a r i t y V a r i a t i o n i n Sulfonate M i c e l l e s . Our results here suggest that a p o l a r i t y gradient i n the inverted micelles of s u l f o n a t e s , e x c l u d i n g the p o l a r c o r e , does e x i s t i n a manner s i m i l a r to the oxygen concentration gradient for the same sulfonates r e p o r t e d p r e v i o u s l y by us 07). E a r l i e r , Wheeler and Thomas (10) e s t a b l i s h e d t h a t the v i b r a t i o n a l f i n e s t r u c t u r e o f bands I I and I I I o f a pyrene d e r i v a t i v e probe can be used t o measure the local p o l a r i t y of a micro-environment i n aggregates. We noted t h a t bands I I and I I I i n the v i b r a t i o n a l f i n e s t r u c t u r e o f PVA f o r both s u l f o n a t e systems has c o m p l e t e l y d i s a p p e a r e d , w h i l e t h a t o f PHA i s retained. The d i s a p p e a r a n c e o f bands I I and I I I i n d i c a t e s t h a t the probe has e x p e r i e n c e d a h i g h l y p o l a r medium. Hence, the p o l a r i t y g r a d i e n t o b s e r v e d here i s r e a s o n a b l y e s t a b l i s h e d d e s p i t e the f a c t t h a t background f l u o r e s c e n c e i n t e r f e r e n c e from the a r o m a t i c m o i e t i e s of s u l f o n a t e s produced c o n s i d e r a b l e uncertainty i n the lifetime v a l u e s measured. The oxygen c o n c e n t r a t i o n g r a d i e n t and p o l a r i t y g r a d i e n t seem to be r e l a t e d . I t i s l i k e l y t h a t the oxygen c o n c e n t r a t i o n g r a d i e n t i s c r e a t e d by the e x i s t e n c e o f the p o l a r i t y g r a d i e n t . More work i s needed to e s t a b l i s h the r e l a t i o n s h i p .


7. JAO AND KREUZ


99

Conclusion 1-Pyrene c a r b o x a l d e h y d e has u t i l i t y as a f l u o r e s c e n t probe i n some i n v e r t e d m i c e l l a r systems c o n t a i n i n g s o l u b i l i z e d i n o r g a n i c species i n the polar core. I t s f l u o r e s c e n c e l i f e t i m e i s c a . 5 n s ; thus i t i s an a p p r o p r i a t e probe f o r measuring m i c e l l a r s i z e s which a r e a p p r o x i m a t e l y 100A. V a r i a t i o n o f l a t e r a l m o b i l i t y ( f l u i d i t y ) and p o l a r i t y g r a d i e n t have been r e a s o n a b l y e s t a b l i s h e d i n c e r t a i n c a l c i u m a l k a r y l s u l f o n a t e m i c e l l e s u s i n g 1-pyrene c a r b o x y l i c a c i d probes w i t h v a r y i n g alkyl chain lengths. The e x i s t e n c e o f a p o l a r i t y g r a d i e n t i n an i n v e r t e d m i c e l l e may be r e s p o n s i b l e f o r t h e c r e a t i o n o f an oxygen c o n c e n t r a tion gradient.


Acknowledgment We acknowledge the c o n t r i b u t i o n o f Mr. James P. B o o l u k o s , c a r r i e d out t h e f l u o r e s c e n c e measurements f o r t h i s s t u d y .

who

Literature Cited 1.

(a) Arkin, L., and Singleterry, C. R. (1948). J. Am. Chem. Soc. 70, 3965; (b) Arkin, L., and Singleterry, C. R. (1949). J. Colloid Sci. 4, 537-539; (c) Singleterry, C. R., and Arkin-Weinberger, L. (1951). J. Am. Chem. Soc. 73, 4574-4579. 2. (a) Wong, Μ., Thomas, J. K., and Gratzel, M. (1976). J. Am. Chem. Soc. 98, 2391-2397; (b) Thomas, J. K. (1984). The Chemistry of Excitation at Interfaces, ACS Monograph 181, ACS, Washington, D.C. 3. (a) Correll, G. D., Chester, III, R. N., Nome, F., and Fendler, J. H. (1978). J. Am. Chem. Soc. 100, 1254-1262; (b) Fendler, J. H. (1982). Membrane Mimetic Chemistry, Wiley, New York. 4. Keh, Ε., and Valeur, Β. (1981). J. Colloid Interface Sci. 79, 465-478. 5. Kalyanasundaram, K., and Thomas, J. K. (1977) J. Phys. Chem. 81, 2176-2180. 6. Love, L. J. Cline, Harbata, J. G., and Dorsey, J. G. (1984). Anal. Chem. 56, 1133A-1148A. 7. Jao, T. C., and Kreuz, K. L. (1984). J. Colloid Interface Sci. 102, 308-310. 8. Galla, H.-J., and Luisetti, J. (1980). Biochim. Biophys. Acta 596, 108-117. 9. Morris, D. A. N., and Thomas, J. K. (1977). In Micellization, Solubilization, and Microemulsions (K. L. Mittal ed.) Plenum Press, New York, Vol. 2, pp. 913-926. 10. Wheeler, J . , and Thomas, J. K. (1982). In Inorganic Reactions in Organized Media (S. L. Holt, ed.) American Chemical Society, Washington, D.C., ACS Symp. Ser. No. 177, pp. 97-111. RECEIVED

February 3, 1986


Characterization of Inverted Micelles of Calcium Alkarylsulfonates by

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