24 Behavior and Applications of Surfactant Mixtures John F. Scamehorn
Downloaded by UNIV LAVAL on February 16, 2013 | http://pubs.acs.org Publication Date: June 5, 1986 | doi: 10.1021/bk-1986-0311.ch024
School of Chemical Engineering and Materials Science, University of Oklahoma, Norman, OK 73019
Future trends in research into the science and technology of surfactant mixtures is discussed. This is a field rich in opportunities for innovative scientific research and also practical applications. Research in this area will dramatically increase in quantity in the next several decades and great progress in the understanding and utilization of surfactant mixtures is expected. Research i n t o t h e c h e m i s t r y and p h y s i c s o-f sur-f a c t a n t mixture behavior has seen a r a p i d i n c r e a s e i n a c t i v i t y over t h e l a s t decade. New t e c h n o l o g i c a l a p p l i c a t i o n s involving sur-f a c t a n t s h a v e e v o l v e d , many o-f w h i c h a r e d e p e n d e n t on t h e u s e o-f s u r f a c t a n t m i x t u r e s . T h e r e i s no r e a s o n t o doubt t h a t new a p p l i c a t i o n s of s u r f a c t a n t m i x t u r e s w i l l c o n t i n u e t o be d i s c o v e r e d and some r e c e n t l y proposed ones w i l l r e a c h l a r g e s c a l e c o m m e r c i a l i z a t i o n . As a r e s u l t o f t h e e c o n o m i c d r i v i n g f o r c e and t h e g r o w i n g awareness of t h e wealth of fascinating scientific phenomena o c c u r r i n g i n m i x e d s u r f a c t a n t s y s t e m s , r e s e a r c h into s u r f a c t a n t mixture behavior w i l l a l s o continue t o increase i n intensity. The n e x t d e c a d e o r t w o p r o m i s e t o be t i m e s o f e x c i t i n g p r o g r e s s i n t h i s f i e l d . Chapter 1 was an o v e r v i e w o f t h i s f i e l d . In t h i s chapter, I w i s h t o d i s c u s s t h e c u r r e n t f o c u s o f work on surfactant mixtures. I will also t r y t o outline the a r e a s i n w h i c h I b e l i e v e r e s e a r c h i s needed i n s u r f a c t a n t mixture behavior. As a r e s u l t , this will be a h i g h l y opinionated, s p e c u l a t i v e , and p e r s o n a l c h a p t e r . I f some of t h e d i s c u s s i o n s t i m u l a t e s c r e a t i v e thought i n other r e s e a r c h e r s , w h e t h e r t h e y a g r e e w i t h me o r n o t , a g o a l o f t h i s c h a p t e r w i l l have been a c h i e v e d . 0097-6156/ 86/ 0311 -0324$06.00/ 0 © 1986 American Chemical Society
In Phenomena in Mixed Surfactant Systems; Scamehorn, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
24. SCAMEHORN
Future Perspectives
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One o f t h e most e n c o u r a g i n g a s p e c t s o f t h i s - f i e l d i s t h e i n c r e a s i n g l y i n t e r n a t i o n a l n a t u r e o-f work i n t h e area. The c h a p t e r s i n t h i s book r e p r e s e n t c o n t r i b u t i o n s •from A u s t r a l i a , Canada, E n g l a n d , J a p a n , P e o p l e s R e p u b l i c o-f C h i n a , U n i t e d S t a t e s , Sweden, and West Germany. This c h a p t e r w i l l be o r g a n i z e d i n t o s e c t i o n s d e a l i n g with t h e v a r i o u s aggregates which s u r f a c t a n t s can form. Applications will be i n c l u d e d a s p a r t o-f t h e d i s c u s s i o n of t h e s e o t h e r t o p i c s .
Downloaded by UNIV LAVAL on February 16, 2013 | http://pubs.acs.org Publication Date: June 5, 1986 | doi: 10.1021/bk-1986-0311.ch024
M i c e l l e Formation Micelles are often present i n surfactant systems. In some p r o c e s s e s , s u c h a s s o l u b i l i z a t i o n , t h e y a r e d i r e c t l y involved. Micelles indirectly affect many other p r o c e s s e s b e c a u s e monomer c o n c e n t r a t i o n s o r a c t i v i t i e s o f t h e s u r f a c t a n t components a r e d i c t a t e d by t h e monomermicelle equilibrium at total surfactant concentrations a b o v e t h e CMC. Therefore, i n t e r e s t i n mixed micelle f o r m a t i o n w i l l c o n t i n u e t o grow. T h e r e a r e some l a r g e g a p s i n o u r k n o w l e d g e o f m i x e d m i c e l l e s which i s s e r i o u s l y impeding p r o g r e s s toward u n d e r s t a n d i n g and q u a n t i f y i n g t h e i r b e h a v i o r . These g a p s are mainly experimental i n nature; i . e . , although improved models a r e needed, t h e r e is little value i n further t h e o r e t i c a l development w i t h o u t c e r t a i n c r i t i c a l d a t a t o compare p r e d i c t i o n s a g a i n s t . S u r f a c t a n t A c t i v i t y i n M i c e l l a r S y s t e m s , The activities or concentrations o f i n d i v i d u a l s u r f a c t a n t monomers i n e q u i l i b r i u m w i t h m i x e d m i c e l l e s a r e t h e most important quantities predicted by m i c e l l a r t h e r m o d y n a m i c m o d e l s . These v a r i a b l e s o f t e n d i c t a t e p r a c t i c a l performance of surfactant solutions. The monomer c o n c e n t r a t i o n s in mixed micellar systems have been measured by ultrafiltration ( 1_) , d i a l y s i s (2) , a c o m b i n a t i o n o f c o n d u c t i v i t y and s p e c i f i c i o n e l e c t r o d e measurements ( 3 ) , a method u s i n g s u r f a c e t e n s i o n o f m i x t u r e s a t and above the CMC (4), g e l f i l t r a t i o n (5), c o n d u c t i v i t y (6), specific ion electrode measurements
