14 Surface Adsorption and Micellization of the Mixed Solution of Fluorocarbon and Hydrocarbon Surfactants Downloaded by PENNSYLVANIA STATE UNIV on February 16, 2013 | http://pubs.acs.org Publication Date: June 5, 1986 | doi: 10.1021/bk-1986-0311.ch014
Guo-Xi Zhao and Bu-Yao Zhu Laboratory of Colloid Chemistry, Department of Chemistry, Peking University, Beijing, People's Republic of China
Various systems of fluorocarbon and hydro carbon surfactant mixtures were investiga ted, By considering the effect of counter -ion on the interactions between the surface active ions, the general equation for c a l culating the interaction parameters in the micelle (β ) and at the surface (β ) have been obtained and applied to the mixed sys tems. It i s shown that: (1) the "mutual phobicity" between FC- and HC-chains i s clearly illustrated by the positive β -values for the anionic-anionic and nonionic-nonionic surfactant mixtures, and by the positive deviation of mixture cmc data from ideal solution theory; (2) for the cationic-anionic surfactant mixtures there are significant synergism and very large negative values of β and β , indicating the great molecular interactions between them; (3) considerable interactions exist in the ionic-nonionic FC- and HC-surfactants system; (4) β -value obviously increa ses with the surface pressure of the mixed solutions (especially in the systems with stronger interactions). m
σ
σ
m
σ
σ
The fluorocarbon (FC) surfactants possess many salient features which can not be found in the common hydrocarbon (HC) surfactants. They are extremely surface active. Dilute aqueous solution may have surface tension values as low as ^ 15 mN«r . They are chemically stable and resistant to heat. The FC-surfactant surface layer formed on a solid renders the solid surface not only hydrophobic but also leophobic. Recently more attention was paid to the investigation of FC-surfactants and mix tures of FC- and HC-surfatants (1-9) partly because of r
0097-6156/86/0311-0184$06.00/0 © 1986 American Chemical Society
In Phenomena in Mixed Surfactant Systems; Scamehorn, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
Downloaded by PENNSYLVANIA STATE UNIV on February 16, 2013 | http://pubs.acs.org Publication Date: June 5, 1986 | doi: 10.1021/bk-1986-0311.ch014
14.
Fluorocarbon and Hydrocarbon Surfactants
ZHAO AND ZHU
185
t h e p r a c t i c a l i m p o r t a n c e of s u r f a c t a n t m i x t u r e w i t h h i g h e r s u r f a c e a c t i v i t y but l o w e r p r i c e t h a n t h e F C - s u r f a c t a n t i t s e l f , and p a r t l y b e c a u s e of t h e t h e o r e t i c a l importance of u n d e r s t a n d i n g t h e p e c u l i a r i t i e s of t h e i n t e r a c t i o n s between t h e CF- and C H - s u r f a c t a n t s . These i n v e s t i g a t i o n s have shown t h a t u n l i k e t h e common H C - s u r f a c t a n t m i x t u r e s , f r e q u e n t l y t h e FC- and H C - s u r f a c t a n t m i x t u r e s c a n n o t f o r m t h e e n t i r e l y m i s c i b l e m i c e l l e s i n t h e mixed s o l u t i o n , but e s s e n t i a l l y t h e i n d i v i d u a l m i c e l l e s of t h e s i n g l e s u r f a c tant. Some of t h e s y s t e m s of FC- and H C - s u r f a c t a n t s e x h i b i t e x t r a o r d i n a r y h i g h i n t e r f a c i a l and s u r f a c e a c t i v i t y , hence s u c h a mixed a q u e o u s s o l u t i o n i s c a p a b l e of s p r e a d i n g on an o i l s u r f a c e ( 9 ) , and c a n be u s e d a s a component i n f i r e - e x t i n g u i s h e r f o r m u l a t i o n s . In o r d e r t o u n d e r s t a n d f u r t h e r t h e e s s e n t i a l n a t u r e of t h e p e c u l i a r i t i e s o f t h e mixed FC- and H C - s u r f a c t a n t s s y s t e m , i n t h i s i n v e s t i g a t i o n t h e s u r f a c e a d s o r p t i o n and m i c e l l e f o r m a t i o n o f some mixed s o l u t i o n s of v a r i o u s t y p e F C - and HCs u r f a c t a n t s and t h e m o l e c u l a r i n t e r a c t i o n s a t t h e i n t e r f a c e and i n m i c e l l e s were s t u d i e d .
Experimental P e r f l u o r o o c t a n o i c a c i d ( C 7 F / 5 C O O H , C F H ) , sodium p e r f l u o r o o c t a n o a t e ( C F , COONa, C F N a ) , sodium d e c y l s u l f a t e ( C ) H2.1 5U4Na, C j o S N a ) , s o d i u m d o d e c y l s u l f a t e (C\z H ^ S u ^ N a , CizSNa), octyltrimethylammonium b r o m i d e ( C 8 H 1 7 N( C H ) B r , C e N B r ) , η - h e p t a n e , s o d i u m c h l o r i d e and s o d i u m b r o m i d e a r e all t h e same a s used i n t h e p r e v i o u s works ( 4 - 7 ) , Triton X-IOOi Rohm & Haas p r o d u c t ( t - C ô H - C H 0 ( C i H 4 O ) , H, TX100). -6203- ( C . o F i a 0 ( C z H 4 0 ) ^ H ) i s u p p l i e d by S h a n g h a i I n s t i t u t e of Organic Chemistry. Octylmethyl sulfoxide ( C g H i S 0 C H , C Ô S O C ) and d e c y l m e t h y l s u l f o x i d e (C ,0 H i i S0CH , C | 5 0 C ) t s y n t h e s i z e d i n our l a b o r a t o r y by t h e t h i o e t h e r o x i d a t i o n method ( w i t h H a 0 a ) ( l 0 ) , and p u r i f i e d by r e p e a t e d r e c r y s t a l l i z a t i o n from petroleum e t h e r . The w a t e r u s e d was t h e d i s t i l l e d d e i o n i z e d w a t e r (Klïln04-treated). S u r f a c e t e n s i o n and i n t e r f a c i a l t e n s i o n (n-heptane/H^O) were d e t e r m i n e d by t h e d r o p - v o l u m e method ( 1 1 ) , The d e n s i t y of s o l u t i o n s f o r c a l c u l a t i n g s u r f a c e and i n t e r f a c i a l t e n s i o n were measured w i t h a U - t u b e p y c n o m e t e r . 7
7
5
7
0
3
l 7
7
6
4
3
0
3
3
O
Theoretical
background
The m i c e l l i z a t i o n of t h e s u r f a c t a n t i n an aqueous s o l u t i o n c a n be r e g a r d e d as a phase s e p a r a t i o n p r o c e s s ( 4 , 1 2 ) , At e q u i l i b r i u m , t h e c h e m i c a l p o t e n t i a l of s u r f a c t a n t component i , / i j , i s e q u a l t o t h a t i n t h e m i c e l l e (JU[ ) 1 m
In
the
solution
of a s i n g l e
surfactant
In Phenomena in Mixed Surfactant Systems; Scamehorn, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
186
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
+ RT
M\
In t h e
In a;, = j U {
s o l u t i o n of s u r f a c t a n t Mi
+ RT
» V'm
In a^
mixture
(3)
• RT In
where a^ i s t h e a c t i v i t y of component i monomer i n t h e solution; f and X >» a r e t h e a c t i v i t y c o e f f i c i e n t and mole f r a c t i o n of i i n t h e m i c e l l e , r e s p e c t i v e l y . In g e n e r a l , t h e s o l u t i o n c o n c e n t r a t i o n of a s u r f a c t a n t a t cmc ( 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 ) i s d i l u t e enough t o assume t h a t m o l a l i t y e q u a l s a c t i v i t y ; equations (2) and (3) become im
Downloaded by PENNSYLVANIA STATE UNIV on February 16, 2013 | http://pubs.acs.org Publication Date: June 5, 1986 | doi: 10.1021/bk-1986-0311.ch014
(2)
m
t
Mi
* RT
l n cmcl
=
μ°»
Mi
•
In
*
M°im •
RT
cmc-
(4) RT
(5)
ln
i n w h i c h cmc! i s t h e cmc of t h e p u r e s u r f a c t a n t i ; cmcj , t h e c o n c e n t r a t i o n of s u r f a c t a n t i monomer a t cmc of t h e mixed s o l u t i o n . F o r the i o n i c s u r f a c t a n t s (1-1 t y p e ) , we s h o u l d t a k e a c c o u n t of t h e e l e c t r i c a l l y c h a r g e d s p e c i e s and t h e pos s i b i l i t y of d o i n g e l e c t r i c a l work. The m i c e l l e may be r e g a r d e d as a c h a r g e d p s e u d o - p h a s e , and t h e c h e m i c a l po t e n t i a l i s r e p l a c e d by t h e e l e c t r o c h e m i c a l p o t e n t i a l (12). The e f f e c t i v e e l e c t r i c a l work i n m i c e l l e f o r m a t i o n i s ( l n ( 2 0 0 0 π σ / υ Έ Τ ) - l n C\
)
2
Ν ο Κ ί β ^ = K; RT
(6)
i n w h i c h No i s t h e A v o g a r d r o number, Κ ; i s a c o n s t a n t r e l a t i n g t o d e g r e e of c o u n t e r i o n b i n d i n g t o t h e m i c e l l e of s u r f a c t a n t i ; e, t h e e l e c t r o n i c c h a r g e ; D, t h e d i e l e c t r i c c o n s t a n t ; C« , t h e c o u n t e r i o n c o n c e n t r a t i o n ; and σ i s t h e s u r f a c e c h a r g e d e n s i t y of t h e m i c e l l e . Then f r o m Eqns, (4) and (5) we have e
- K-
l n c\
(7)
ln
cmc? « Ao
In
( CmC; /fim X»m ) « A. - K;
t
(8)
In Cr
i n which A i s a c o n s t a n t (* ( Mïi, - M Î ' ) / R T • Κ ι l n (2000 TtcrVbRT ) ) C £ , t h e c o n c e n t r a t i o n of c o u n t e r i o n i n t h e mixed s o l u t i o n . C o m b i n i n g E q n s . (7) and ( 8 ) , we have c
f
fimXim For binary t i o n s h i p may be In
and
f|
In f ^
» (cmc;/cmcl)(Cr/C ')
Ki
m i x t u r e s y s t e m s , a s i m p l e fim — Xtm obtained from s o l u t i o n theory; «
w
m
(9)
l
rela
fimXJtm
«PwXÎm
In Phenomena in Mixed Surfactant Systems; Scamehorn, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
(t0)
(10)
14.
ZHAO AND ZHU
Fluorocarbon and Hydrocarbon Surfactants
187
i n w h i c h /3 i s t h e m o l e c u l a r i n t e r a c t i o n p a r a m e t e r between two s u r f a c t a n t s i n t h e m i c e l l e . Combining these two r e l a t i o n s h i p s w i t h E q u a t i o n 9.,we o b t a i n m
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(11) From t h e v a r i o u s c o n c e n t r a t i o n v a l u e s and K i , Ko ( i n g e n e r a l , b a s e d on t h e t h e o r e t i c a l and e x p e r i m e n t a l r e s u l t s (12,14), v a l u e s f o r v a r i o u s 1-1 i o n i c s u r f a c t a n t s a r e a p p r o x i m a t e l y ^-0. 6 ) , e q u a t i o n 110) c a n be s o l v e d iteratively forX and X i and y6 i s o b t a i n e d s i m u l taneously. In t h e c a s e where e x c e s s i n o r g a n i c s a l t i s added o r t h e c o u n t e r i o n c o n c e n t r a t i o n i s h e l d c o n s t a n t , i . e . C{ = C J , t h e n e q u a t i o n (10) becomes 1 m
2 m
m
/3m = l n ( c m c i / c m c ? X , ) / *lm - l n (cmc /cmcjX**)/xf m
a
m
(12)
T h i s equation i s applied to the nonionic surfactant system a s w e l l . In t h e c a s e o f s u r f a c e a d s o r p t i o n , a t c o n s t a n t surf a c e t e n s i o n o f s o l u t i o n s , an e q u a t i o n o f t h e same f o r m a s e q u a t i o n 12 i s o b t a i n e d f o r t h e b i n a r y s u r f a c t a n t mixt u r e system (15,16): Ar
= l n ( C . / C Î X , * ) / Χ|β· = I n ( C / C | X . ) / Χ ? 2
ao
σ
(13) i n w h i c h p
