Phenomena in Mixed Surfactant Systems - American Chemical Society

5 Solution Properties of Mixed Surfactant Systems The Interaction Between Azo Oil Dyes and Mixed Surfactant Systems Keizo Ogino and Masahiko Abe

Downloaded by HARVARD UNIV on June 17, 2014 | http://pubs.acs.org Publication Date: June 5, 1986 | doi: 10.1021/bk-1986-0311.ch005

Faculty of Science & Technology, Science University of Tokyo, 2641 Yamazaki, Noda, Chiba 278, Japan

Solution properties of anionic-nonionic mixed surfactant systems have been investigated with addition of azo oil dyes; 4-phenylazo1-naphthylamine (4-NH ) and 4-phenylazo-1-naphthol (4-OH). The interaction of 4-NH with sodium dodecyl sulfate (SDS) was enhanced by the addition of alkyl poly(oxyethylene) ethers (C POE ) surfactants which have a longer alkyl chain and/or fewer ethyleneoxide groups. The fading phenomena was obserbed when 4-OH was added into the mixed surfactant systems, and its rate of 4-OH accelerated by increasing the alkyl chain length or decreasing the number of ethyleneoxide groups in the CΡΟΕn molecule. The interactions of azo oil dyes with mixed surfactant systems would be larger for the system which is easy to form a mixed micelle than for the system which coexists two kinds of micelles. 2

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Mixed surfactant systems are of importance from a fundamental and practical point of view. Therefore, many recent papers have reported on the micellar properties of mixed surfactant solutions (1-9). For example, Tokiwa et al. have measured the NMF spectra (4_) ; Ingram has measured surface tension (5). Previously, we have reported the solution properties of anionic-nonionic surfactant mixed systems from the point of view of electrical (6,7) and surface tension measurements (8-10), and investigated the mixed micelle formation. We have discussed the differences in the mixed micelle forming due to the different alkyl chain lengths (ACL) and/or polyoxyethylene chain lengths (PCL) in nonionic surfactants. We found that the mixed micelle would be formed more easily by a nonionic surfactant including long ACL (or shorter PCL) than by one having shorter ACL (or long PCL). We have also reported that the protonation of 4-phenylazo-l-naphthylamine (4-NH2) was caused by 0097-6156/ 86/ 0311 -0068$06.00/ 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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sodium d o d e c y l s u l f a t e (SDS) m i c e l l e s (11,12). We have, moreover, mentioned t h e e f f e c t o f PCL and/or ACL i n n o n i o n i c s u r f a c t a n t m o l e c u l e on t h e tautomerism o f 4 - p h e n y l a z o - l - n a p h t h o l (4-OH)(13). In t h i s paper, we r e p o r t t h e s o l u t i o n p r o p e r t i e s o f sodium d o d e c y l s u l f a t e ( S D S ) - a l k y 1 p o l y ( o x y e t h y l e n e ) e t h e r ((^ΡΟΙ^) mixed systems w i t h a d d i t i o n o f a z o o i l dyes (4-NH , 4-OH). The 4-NHo dye i n t e r a c t s w i t h a n i o n i c s u r f a c t a n t s such a s SDS (11,12), w h i l e 4-OH dye i n t e r a c t s w i t h n o n i o n i c s u r f a c t a n t s s u c h a s C POEn ( 1 3 ) . However, 4-NH2 i s dependent on t h e m o l e c u l a r c h a r a c t e r i s t i c s o f t h e n o n i o n i c s u r f a c t a n t i n t h e a n i o n i c - n o n i o n i c mixed s u r f a c t a n t systems, w h i l e i n t h e c a s e o f 4-OH, t h e f a d i n g phenomena o f t h e dye i s observed i n the s o l u b i l i z e d s o l u t i o n . T h i s f a d i n g r a t e i s dependent on t h e m o l e c u l a r c h a r a c t e r i s t i c s o f n o n i o n i c s u r f a c t a n t as w e l l a s mixed m i c e l l e f o r m a t i o n . We d i s c u s s t h e d i f f e r e n c e s i n s o l u t i o n p r o p e r i e s o f azo o i l dyes i n t h e d i f f e r e n t mixed s u r f a c t a n t systems. 2


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A n i o n i c s u r f a c t a n t : Sodium d o d e c y l s u l f a t e (SDS, C 2 2 5 3 ^ s u p p l i e d by N i h o n S u r f a c t a n t I n d u s t r i e s Co., L t d Tokyo, Japan. I t was e x t r a c t e d w i t h e t h e r and r e c r y s t a l l i z e d from e t h a n o l . The p u r i t y was a s c e r t a i n e d by s u r f a c e t e n s i o n measurement. Nonionic surfactant: A l k y l poly(oxyethylene) ether (C POE , C H2m+lO(CH2CH 0)2oH, m=12, 14, 16, and 18; C H 3 0 ( C H 2 C H 0 ) H , n=10, 20, 30, and 40) were s u p p l i e d by N i h o n S u r f a c t a n t I n d u s t r i e s Co., L t d . These have a narrow m o l e c u l a r weight d i s t r i b u t i o n . Azo o i l dye: The s y n t h e s i s and p u r i f i c a t i o n o f 4 - p h e n y l a z o 1-naphthylamine ( 4 - N H 2 ) , 4 - p h e n y l a z o - l - n a p h t h o l (4-OH) were d e s c r i b e d i n o u r p r e v i o u s paper ( 1 4 ) . Water used i n t h i s experiment was t w i c e d i s t i l l e d and was d e i o n i z e d b y an ion-exchange i n s t r u m e n t (ΝΑΝΟ pure D-1791 o f B a r n s t e a d Co., L t d . ) ; i t s r e s i s t i v i t y was about 18.0 megohm'cm and i t s pH was 6.7. 1

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Method P r e p a r a t i o n o f s u r f a c t a n t s o l u t i o n s i n c l u d i n g o i l dye. I. F o r 4 - N H 9 dye. F i r s t , i n t o s e v e r a l 100 ml g l a s s - s t o p p e r e d E r l e n m e y e r f l a s k s , 25 ml p o r t i o n s o f a g i v e n c o n c e n t r a t i o n o f p u r e s u r f a c t a n t s o l u t i o n were p l a c e d . Next a measured amount o f 4-NH (5.0 χ 1 0 ~ mol/1) was added t o each s o l u t i o n . The m i x t u r e were s t i r r e d u l t r a s o n i c a l l y f o r 5 min and t h e n a g i t a t e d w i t h a s h a k e r (Model SS-82D t y p e o f Tokyo R i k a k i k a i Co., L t d , Tokyo, Japan) f o r 24 h r and a l l o w e d t o s t a n d f o r 24 h r i n a t h e r m o s t a t a t 30°C i n order t o established a s o l u b i l i z a t i o n equilibrium. After the e q u i l i b r i u m had been e s t a b l i s h e d , t h e s e p u r e a n i o n i c s u r f a c a n t s o l u t i o n s i n c l u d i n g 4 - N H 2 were mixed w i t h pure n o n i o n i c surfactants s o l u t i o n s i n v o l v i n g one. 5

I I . F o r 4-OH dye. I n t o s e v e r a l 100 ml f l a s k s , 25 m l p o r t i o n s o f a g i v e n c o n c e n t r a t i o n o f a n i o n i c s u r f a c t a n t s o l u t i o n were p l a c e d , f o l l o w e d by a d d i t i o n o f a g i v e n c o n c e n t r a t i o n o f n o n i o n i c s u r f a c t a n t s o l u t i o n . The m i x t u r e s were s t i r r e d f o r 1 h r i n a t h e r m o s t a t a t 30°C i n o r d e r t o e s t a b l i s h t h e i r e q u i l i b r i a , and t h e n


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a measured amount o f 4-OH (5.0 mixed s u r f a c t a n t s o l u t i o n .

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D e t e r m i n a t i o n o f maximal a b s o r p t i o n wavelength ( \ n ) and o p t i c a l d e n s i t y o f each s o l u t i o n " " The measurement was the same a s t h a t d e s c r i b e d i n the p r e v i o u s paper (13), except t h a t t h e s p e c t r o p h o t o m e t e r used was a model MPS-2000 d o u b l e beam type (Shimadzu Co., Tokyo, Japan) w i t h a q u a r t z c e l l (10.Ô mm i n l i g h t pass l e n g t h ) . ax

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(1) P r o t o n a t i o n e q u i l i b r i u m of 4-NH? Matsuoka (15) s u g g e s t s t h a t , when t h e p r o t o n goes t o β-azo-nitrogen atom, e l e c t r i c charge t r a n s f e r o c c u r s ; a s a r e s u l t , a n i t r o g e n atom o f amino group becomes p o s i t i v e l y charged ( q u i n o i d a l form) . The protonation e q u i l i b r i u m occurred i n s o l u t i o n s o f anionic surfactant l i k e SDS which have a s t r o n g l y a n i o n i c h y d r o p h i l i c group (11,14). On the o t h e r hand, t h i s azo form was o b s e r v e d i n o t h e r s u r f a c t a n t m i c e l l e s o l u t i o n s such a s sodium l a u r a t e (11) and n o n i o n i c s u r f a c t a n t s (16). The maximal a b s o r p t i o n wavelength i s a t 535 nm ( q u i n o i d a l form) i n t h e SDS s o l u t i o n , w h i l e a t 450 nm (azo one) i n the C P 0 E s o u t i o n . m

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(1*1) E f f e c t o f a l k y l c h a i n l e n g t h i n CmPOEn on the a b s o r p t i o n spectra. The r e l a t i o n s h i p between the a b s o r p t i o n s p e c t r a and the mixed molar r a t i o o f the S D S - C i 2 2 0 s u r f a c t a n t system i s shown i n Fig.l. The maximal a b s o r p t i o n wavelength almost s h i f t s t o 450 nm w i t h i n c r e a s i n g the molar r a t i o o f C]_2 O 20» absorption at 535 nm by the q u i n o i d a l form o f 4-NH2 does not appear. T h i s seems t o be a r e s u l t o f the d i f f e r e n c e i n the s o l u b i l i z i n g power and the v a l u e o f the cmc o f each pure s u r f a c t a n t . In the former, C12POE20 i s about 15-times l a r g e r , and i n the l a t t e r , C P 0 E i s about 100times smaller. Therefore, a t a given c o n c e n t r a t i o n , a s o l u t i o n of CmPOEn has much more s u r f a c t a n t i n the m i c e l l a r phase t h a n a s o l u t i o n o f SDS. These m i c e l l e s o f Ci2POE Q s o l u b i l i z e d 4-NH more than d i d SDS m i c e l l e s . F i g u r e 2 r e p r e s e n t s the case o f SDSCi8 OE20 mixed systems. The s h i f t o f the maximal a b s o r p t i o n wavelength i s not r e m a r k a b l e l i k e t h a t i n F i g . l . Even the molar r a t i o o f C18POE20 i n c r e a s e s up t o 0.5, the a b s o r p t i o n s p e c t r a c o r r e s p o n d i n g t o t h e q u i n o i d a l form o f 4-NH2 s t i l l r e m a i n s . As t h e a l k y l c h a i n l e n g t h o f C P0E2Q i s i n c r e a s e d , i t seems t h a t the m i c e l l e becomes the more s t a b l e f o r the q u i n o i d a l form o f 4-NH2 and the a b s o r p t i o n s p e c t r a c o r r e s p o n d i n g t o the q u i n o i d a l form o f 4-NH2 i s more pronounced a t the same mixed molar r a t i o o f the s u r f a c t a n t s . POE

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(1«2) E f f e c t o f p o l y o x y e t h y l e n e c h a i n l e n g t h i n C P 0 E on the absorption spectra. I n the c a s e o f SDS-CièPOE^Q mixed s u r f a c t a n t system, t h e maximal a b s o r p t i o n w a v e l e n g t h almost s h i f t s t o 535 nm except f o r the pure n o n i o n i c , and t h e n the peak a t 450 nm disappear. For SDS-C-J^POE^Q mixed system, the maximal a b s o r p t i o n wavelength almost s h i f t s t o 450 nm r e g a r d l e s s o f the molar r a t i o , and the a b s o r p t i o n a t 535 nm i s v e r y weak. T h i s i s enhanced by the d i f f e r e n c e i n the s o l u b i l i z i n g power f o r 4-NH2 as was o b s e r v e d i n m

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the SDS-Ci2 0E2Q system. A t t h e same mixed molar r a t i o o f t h e s u r f a c t a n t s , s h o r t e r t h e p o l y o x y e t h y l e n e c h a i n l e n g t h , t h e more s t a b l e t h e m i c e l l e becomes f o r s o l u b i l i z a t i o n o f t h e q u i n o i d a l form o f 4 - N H 2 and t h e a b s o r p t i o n s p e c t r a c o r r e s p o n d i n g t o t h e q u i n o i d a l one i s e a s i l y r e c o g n i z e d . E s p e c i a l l y i n t h e c a s e o f t h e SDSCifcPOEiQ mixed s u r f a c t a n t system, t h e a b s o r p t i o n a t 535 nm i n c r e a s e s r e m a r k a b l y . T h i s seems t o be due t o the e f f e c t o f t h e low HLB v a l u e o f C ^ P O E ^ ) . (1*3) E x a m i n a t i o n o f mixed m i c e l l e f o r m a t i o n . We have s t u d i e d t h e mixed m i c e l l e f o r m a t i o n o f p o l y o x y e t h y l e n e c a r b o x y l a t e and C POEn systems by e l e c t r i c measurements (17,18) and s u r f a c e t e n s i o n measurements ( 8 - 1 0 ) . We found t h a t the mixed m i c e l l e was formed more e a s i l y by a n o n i o n i c s u r f a c t a n t i n c l u d i n g l o n g ACL (or s h o r t e r PCL) t h a n by one h a v i n g s h o r t e r ACL ( o r l o n g PCL). We have a l s o o b t a i n e d almost t h e same mentioned above f o r S D S - C P 0 E systems (19). The model o f mixed m i c e l l e f o r m a t i o n i s showm i n F i g . 3 t o summarize the coments above. When SDS and CmPOEn a r e mixed, mixed m i c e l l e s form e a s i e r a s the number o f carbons i n the a l k y l c h a i n s i n c r e a e d and the number o f e t h y l e n e o x i d e groups i s d e c r e a s e d on t h e C P 0 E n s u r f a c t a n t . T h i s tendency o f C P 0 E n i s a c c o r d w i t h the t r e n d o f HLB v a l u e s o f C P 0 E n . The l o w e r the HLB v a l u e o f C P 0 E , t h e g r e a t e r i n t e r a c t i o n w i t h SDS, and t h e q u i n o i d a l form o f 4 - N H 2 appears t o be s t a b l i z e d i n the mixed m i c e l l e . On the o t h e r hand, t h e fewer c a r b o n atoms and/or the more e t h y l e n e o x i d e groups CmPOEn has, t h e i n t e r a c t i o n between C P 0 E n and SDS d e c r e a s e , and t h e y seem t o form two t y p e o f m i c e l l e s , one r i c h i n i o n i c the o t h e r r i c h i n nonionic. I n t h i s c a s e , the azo form o f 4 - N H 2 i s more s t a b l e due t o t h e s o l u b i l i z i n g power o f CmPOEn.


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(2) Tautomerism e q u i l i b r i u m o f 4-OH M i t s u i s h i e t a l . d e s c r i b e d (20) t h a t 4-OH was i n the hydrazo form i n p o l a r s o l v e n t s , and azo form i n n o n p o l a r s o l v e n t s . I t was suggested t h a t one hydrogen atom o f the h y d r o x i d e group a t t h e 4 - p o s i t i o n o f the n a p h t h a l e n e r i n g t r a n s f e r r e d t o t h e β-position o f the azo group, and t h e tautomerism was e s t a b l i s h e d between h y d r a z o form o f the k e t o t y p e and the a z o form o f the e n o l t y p e . In t h i s s t u d y , we c o n s i d e r t h a t t h e spectrum w i t h a peak a t t h e 480 nm c o r r e s p o n d s t o t h e former and t h a t a t t h e 415 nm t o t h e l a t t e r i n aqueous s o l u t i o n s o f C P0En s u r f a c t a n t . The 4-OH goes i n t o the a z o form when i t i s s o l u b i l i z e d i n the c a r b o n c o r e o f C^POEn m i c e l l e s . On the o t h e r hand, 4-OH becomes h y d r a z o form when s o l u b i l i z e d i n the p o l y o x y e t h y l e n e c h a i n . F i g u r e 4 demonstrates the a b s o r p t i o n s p e c t r a o f 4-OH i n pure SDS, pure C16POE20 and m i x t u r e s o f t h e s e s u r f a c t a n t s . As can be seen from F i g . 4 , t h e X x o f 4-OH appears a t 480 nm i n the SDS s o l u t i o n , on the o t h e r hand, a t 415 nm i n t h e C16POE20 s o l u t i o n and a s h o u l d e r appears a t 480 nm. Tautomerism o f 4-OH i s a l s o o b s e r v e d i n t h e s e mixed s o l u t i o n . Time dependence o f o p t i c a l d e n s i t y o f 4-OH a t two peaks a r e not o b s e r v e d i n the s i n g l e solutions. m

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(2*1) F a d i n g phenomena o f 4-OH. One s p e c i a l e f f e c t on 4-OH i s t h e f a d i n g phenomena o f t h e dye o b s e r v e d i n the mixed s u r f a c t a n t systems. Time dependence o f t h e a b s o r p t i o n s p e c t r a o f 4-OH i n t h e mixed s o l u t i o n i s shown i n F i g . 5 . The absorbances a t b o t h 415 and



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480 nm d e c r e a s e w i t h t i m e . T h i s f a d i n g phenomena i s a l s o o b s e r v e d f o r o t h e r a n i o n i c s u r f a c t a n t s ; f o r example, p o l y o x y e t h y l e n e c a r b o x y l a t e and sodium d o d e c y l b e n z e n e s u l f o n a t e . The change o f t h e a b s o r b a n c e a t 480 nm i s p l o t t e d a g a i n s t t i m e i n F i g . 6 . The a b s o r b a n c e a t 480 nm i n each s u r f a c t a n t s o l u t i o n i s i n d e p e n d e n t o f t i m e and i s c o n s t a n t . In t h e mixed s o l u t i o n , t h e a b s o r b a n c e a t 480 nm d e c r e a s e s w i t h t i m e , and f a d i n g phenomena o f 4-0H i s o b s e r v e d . The a b s o r b a n c e becomes a minimum i n t h e v i c i n i t y o f m o l a r r a t i o o f SDS/Ci6P0E20 l/l. On t h e o t h e r hand, a f a d i n g e f f e c t l i k e t h i s i s not r e c o g n i z e d i n c a t i o n i c - n o n i o n i c s u r f a c t a n t mixed systems. Namely, t h e f a d i n g phenomena o f 4-OH seems t o a r i s e from t h e system which c o n s i s t s o f a n i o n i c s u r f a c t a n t h a v i n g s t r o n g l y p o l a r groups and n o n i o n i c s u r f a c t a n t . I t seems t h a t t h e i n t e r a c t i o n between h y d r o p h i l i c groups o f SDS and C ^ O E ^ p a r t i c i p a t e i n f a d i n g phenomena o f 4-OH.


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(2*2) E f f e c t o f a l k y l c h a i n l e n g t h and o x y e t h y l e n e g r o u p s i n C P 0 E on t h e f a d i n g r a t e . The e f f e c t o f t h e number o f c a r b o n atoms on t h e f a d i n g r a t e i s shown i n F i g . 7 . As c a n be seen from Fig.7, f o r longer a l k y l chain lengths, the fading r a t e a c c e l e r a t e s i n t h e mixed s u r f a c t a n t systems. The o p p o s i t e e f f e c t o f e t h y l e n e o x i d e groups i s shown i n F i g . 8 . As t h e PCL d e c r e a s e s , t h e f a d i n g r a t e a c c e l e r a t e s i n t h e mixed systems. From F i g s . 7 and 8, t h i s phenomena i s dependent on t h e m o l e c u l a r c h a r a c t e r i s t i c s o f CJJJPOE^ added t o t h e mixed s u r f a c t a n t systems. We found t h a t , f o r n o n i o n i c s u r f a c t a n t i n c l u d i n g l o n g ACL ( o r s h o r t e r P C L ) , t h e mixed m i c e l l e i s formed more e a s i l y t h a n o t h e r s ; f o r one h a v i n g s h o r t e r ACL ( o r l o n g P C L ) , t h e r e a r e two k i n d s o f m i c e l l e s c o e x i s t i n g (one r i c h i n a n i o n i c s u r f a c t a n t and t h e o t h e r r i c h i n n o n i o n i c surfactant) (8,9,17-19). T h e r e f o r e t h e f a d i n g phenomena o f 4-OH i n t h e mixed s u r f a c t a n t systems a p p e a r s t o be r e l a t e d t o t h e mixed m i c e l l e f o r m a t i o n o f SDS and C ^ O E ^ . m

n

(2·3) E f f e c t o f oxygen on t h e f a d i n g r a t e . We must c o n s i d e r why the f a d i n g phenomena o f 4-OH o c c u r s o n l y i n a n i o n i c - n o n i o n i c mixed surfactant solutions. The mixed s o l u t i o n a f t e r b u b b l i n g 0 gas a c c e l e r a t e s t h e f a d i n g r a t e , w h i l e t h a t a f t e r b u b b l i n g N gas decelerates. B a l l e t a l . (21) have r e p o r t e d t h e p h o t o f a d i n g o f 4-OH i n f i l m s o f polymer s u b s t r a t e s . They have d e s c r i b e d t h a t p h o t o f a d i n g o f 4-OH i s caused by o x i d a t i v e a t t a c k on t h e ground s t a t e h y d r a z o form by s i n g l e t oxygen. G r i f f i t h e t a l . ( 2 2 ) have a l s o stated that the photochemical o x i d a t i o n of 4 - a r y l a z o - l n a p h t h o l s a r e caused by t h e o x i d a t i o n o f s i n g l e t oxygen. Kousaka e t a l . ( 2 3 ) have d e s c r i b e d t h a t t h e s o l u b i l i t y o f oxygen i n c r e a s e s w i t h i n c r e a s i n g s u r f a c t a n t c o n c e n t r a t i o n because o f the p e n e t r a t i o n of i t i n t o m i c e l l e s . However, t h i s f a d i n g phenomena does n o t t a k e p l a c e i n s i n g l e ( o r pure) o r mixed s u r f a c t a n t s o l u t i o n s (cationic-nonionic). M e r k e l e t a l . ( 2 4 ) have d e c l a r e d t h a t t h e l i f e t i m e o f s i n g l e t oxygen i s a p p r o x i m a t e l y 10 t i m e s s h o r t e r i n H 0 than i n D2O. I t can be s p e c u l a t e d t h a t , when t h e t r a n s i t i o n energy o f t h e oxygen i s n o t exchanged t o t h e i n t e r n a l e n e r g y o f t h e w a t e r , mainly t o t h e v i b r a t i o n a l energy o f the water molecule, the s i n g l e t oxygen l i f e t i m e makes l o n g . The l o n g l i f e t i m e o f s i n g l e t oxygen can make t h e f a d i n g r a t e o f 4-OH f a s t e r . 2

2

2

We have found t h a t t h e f a d i n g r a t e becomes f a s t e r under t h e


OGINO A N D A B E


Concn. of surfactants 1.0 χ 10~ mol dm-3 2

Concn. of 4-OH 3

5.0 χ 10" mol dm" 5

Time (hour) 0 3


Phenomena in Mixed Surfactant Systems - American Chemical Society

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