13
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The Effect of Alkyl Alcohols on the Surface Adsorption and Micellization of Fluorocarbon and Hydrocarbon Surfactants Bu-Yao Zhu, Guo-Xi Zhao, and Jun-Gang Cui Laboratory of Colloid Chemistry, Department of Chemistry, Peking University, Beijing, People's Republic of China
Mixed aqueous solution of alkyl alcoholC F COONa (I) and alkyl alcohol-C H SO Na (II) were investigated by surface tension analysis. The cmcs of mixtures of (I) and (II) were mostly lower than those of the two pure surfactants, but the reduction of cmc in the systems with fluorocarbon surfactant is less than that with hydrocarbon surfactant, although the cmcs of the fluorocarbon surfactant and the hydrocarbon surfactant are nearly the same. The saturated surface adsorptions of the mixtures are larger than those of the pure surfactants, and the over average molecular areas of the mixtures are smaller accordingly. A l l these facts,combined with the results of molecular interaction parameter calculations, show that alcohol could enhance the adsorption and micellization of both anionic surfactants; also, the mutual phobicity between fluorocarbon and hydrocarbon chains i s revealed in the alkyl alcohol-C F COONa systems. 7
15
10
7
21
4
15
The addition of an alkyl alcohol to the aqueous solution of an ionic surfactant greatly influences the surface act i v i t y of the surfactant. The c r i t i c a l micelle concentration (cmc) of the surfactant becomes lower in presence of alkyl alcohol, and the surface tension of the aqueous solution at cmc reaches a much lower value (1-4). However, no systematic investigation of adsorption and micellization of the alcohol-fluorocarbon (PC) surfactant mixture has been made. Other studies have examined the "mutual phobicity" between the hydrocarbon (HC) and FC chain in the mixed system of FC and HC surfactants (5-10) It i s expected that "mutual phobicity** should be observed in the alkyl alcohol-FC surfactant system.too. In this 0097-6156/ 86/ 0311 -0172S06.00/ 0 © 1986 American Chemical Society
In Phenomena in Mixed Surfactant Systems; Scamehorn, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
13.
Effect of Alkyl Alcohols on Surfactants
ZHU ET AL.
173
p a p e r , s u r f a c e c h e m i c a l p r o p e r t i e s o f mixed aqueous s o l u t i o n o f a l k y l a l c o h o l (R0H)-C F,5 COONa ( C F N a ) and ROHCio H j 5Ο4.Na ( C , 5 N a ) have been i n v e s t i g a t e d = n-C^Hn , n-C$H, , n-C His , n-C H, ) . The e f f e c t o f ROH on 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 i z a t i o n o f C F N a and C , 5 n a 7
2
7
0
3
7
8
T
7
uiere
0
compared.
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Experimental The a l k y l a l c o h o l s a r e o f c h e m i c a l l y pure g r a d e and r e d i s t i l l e d , b o i l i n g p o i n t range* n - C H 0 H ( C 5 O H ) , 137.31 3 8 . 0 C î n - C H , 0 H ( C 0 H ) , 156» 8-157.1° C J n - C H OH ( C OH ) , 1 7 5 . 8 - 1 7 6 . 0 ° C | n-C H, OH ( C 0 H ) , 194.2-194.Q°C. C FNa and C , 5 N a a r e t h e same a s u s e d i n t h e p r e v i o u s uiorks ( 5 ) . The w a t e r u s e d f o r p r e p a r i n g s o l u t i o n s was o b t a i n e d f r o m d i s t i l l a t i o n o f t h e i o n - e x c h a n g e water p r e t r e a t e d w i t h p o t a s s i u m permanganate. Surface t e n s i o n of the w a t e r (30°C) was 71.4 mNm- ( t h e l i t e r a t u r e v a l u e i s 71.18 mNm-» (11)). S u r f a c e t e n s i o n ( 3 0 ° C ) o f t h e s o l u t i o n was 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 2 ) . The d e n s i t y o f t h e s o l u t i o n needed f o r c a l c u l a t i n g t h e s u r f a c e t e n s i o n was meas u r e d by a U - t u b e p y c n o m e t e r . 5
n
e
6
3
6
8
7
7
7
J 5
7
8
0
1
Results
and D i s c u s s i o n s
Surface A c t i v i t y . I t i s o b v i o u s f r o m t h e 7-log C plots ( F l g . l and 2) t h a t t h e a d d i t i o n o f a l k y l a l c o h o l r e s u l t s i n l o w e r i n g b o t h t h e s u r f a c e t e n s i o n and. t h e cmc. I n p a r t i c u l a r , i t i s worth n o t i n g t h a t the s u r f a c e t e n s i o n of t h e mixed s o l u t i o n a t cmc,Terne» i s s i g n i f i c a n t l y l o w e r t h a n t h e s u r f a c e t e n s i o n a t t h e pure s u r f a c t a n t cmc. Cmc and 7cwc o f 111 ( m o l a r r a t i o ) R 0 H - 5 u r f a c t a n t mixed s y s t e m s were shown i n T a b l e 1. % o f R0H-C FNa s o l u t i o n r e a c h e s m
Table
1.
C 0H-C FNa C 0H-C FNa C 0H-C FNa C 0H-C FNa Pure C F N a 7
6
7
7
7
8
7
7
C5OH-C0
SNa
C OH-C,o C 0H-C C 0H-C Pure C,o
SNa SNa SNa SNa
6
7
I0
e
lo
7
7cwc and cmc o f l i l R O H - S u r f a c t a n t Mixture S o l u t i o n s (with NaCl, I o n i c S t r e n g t h : 0.1m; a t 3 0 ° C )
ROH-Surf a c t a n t 5
c
7cm
C
(mNm-' )
20.8 16.0 16.2 17.4 24.4 33.5 28.0 23.0 22.4 37,4
cmc 1.45 1.35 7.70 3.30 1.48 1.48 1.37 7.76 3.10 1.53
(m) X X X X X X X X X X
10~ 10-
In Phenomena in Mixed Surfactant Systems; Scamehorn, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
3
2
174
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
a minimum v a l u e of ^ 1 6 mNm-' (RDH = C$0H and C D H ) uihereas t h e Time o f C F N a s o l u t i o n i s < v 2 4 mNm-' , and t h e l o w e s t v a l u e o f T^mc o f R0H-C, SNa s o l u t i o n i s a b o u t 22-23 mNm-' (ROH = C 0 H and C 0 H ) . A l l t h e s e f a c t s show t h a t t h e surf a c e a c t i v i t y o f FC s u r f a c t a n t can be g r e a t l y e n h a n c e d by t h e a d d i t i o n o f a l k y l a l c o h o l s , t h i s c o u l d be o f g r e a t p r a c t i c a l s i g n i f i c a n c e , b e c a u s e we may o b t a i n h i g h e r s u r f a c e a c t i v i t y u s i n g a s m a l l e r amount o f e x p e n s i v e FC s u r factant. 7
7
0
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7
e
Surface Adsorption. From F i g . l and F i g . 2 we c a n c a l c u l a t e t h e t o t a l s u r f a c e a d s o r p t i o n (£^) o f t h e R O H - s u r f a c t a n t m i x t u r e by a p p l y i n g t h e G i b b s a d s o r p t i o n e q u a t i o n ( 7 ) . I n t h e c a s e o f a mixed a q u e o u s s o l u t i o n w i t h a c o n s t a n t i o n i c s t r e n g t h , the e q u a t i o n i s w r i t t e n as -d?/RT
d
= Ic p-(orC S-) 7
l
n
l0
ro^-corCcS-) * IROH
D
L
N
M
1
t
ROH
)
where y i s t h e s u r f a c e t e n s i o n o f s o l u t i o n , Ic r-
