Emulsion Polymers and Emulsion Polymerization - American

15 The Relationship Between the Electrophoretic Mobility and the Adsorption of Ions on Polystyrene Latex 1

Downloaded by PURDUE UNIVERSITY on June 13, 2013 | http://pubs.acs.org Publication Date: October 7, 1981 | doi: 10.1021/bk-1981-0165.ch015

C. M. MA , F. J. MICALE, M. S. EL-AASSER, and J. W. VANDERHOFF Department of Chemistry, Center for Surface and Coatings Research, Sinclair Laboratory #7, Lehigh University, Bethlehem, PA 18015 The stability of latexes is important for many industrial applications and in theoretical research. One of the measures of the stability is the electrophoretic mobility or zeta potential of the latex particle. Thus far the chemisorbed surface charge groups have been considered as the dominant factor determine the ζ potential. In a previous paper (1), we concluded that the origin of surface charge on polystyrene latex was not simply the charged ionizable groups on the surface of the latex particle,and that the hydrophobic surface of the latex might be playing a more signifi cant role in the origination of the surface charge. In this work, the relationship between electrophoretic mobility and surface charge of latexes, especially the effect of the adsorption of ions from solution on the electrophoretic mobility of polystyrene latex particles, was investigated in more detail. The possible mechan isms of the origination of the surface charge on latex particles are the specific objectives of this investigation. Experimental The latexes investigated were the 357 nm Dow monodisperse polystyrene (LS-1010) and two polydisperse polystyrene latexes prepared in our laboratory (2) where the concentration of func tional monomer, Cops II (Alcolac-ammonium salt of a short chain vinyl sulfonate), added to the recipe was 10 and 10 M for C and C , respectively. The latexes were cleaned by using a mixed ion-exchange resin bed (3). The number of acid surface groups were determined by using a conductometric titration technique (4). Initially the latexes contained only sulfate groups and a small concentration of hydroxyl groups. One of the latexes was hydrolized at 90°C for 120 hrs in order to convert the surface sulfate groups to hydroxyl groups. The electrophoretic mobility of the latexes was measured at 25°C by using a Rank-microelectrophoresis. ^Visiting Research Scientist, Peking University, Peking, Peoples Republic of China. -3

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0097-6156/81/0165-0251 $05.00/0 © 1981 American Chemical Society

In Emulsion Polymers and Emulsion Polymerization; Bassett, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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The a d s o r p t i o n o f s o d i u m l a u r y l s u l p h a t e o n PS l a t e x was d e termined by u s i n g a d i f f e r e n t i a l r e f r a c t o m e t e r ( 5 ) . The s o d i u m l a u r y l - s u l f a t e was a p r o d u c t o f E a s t m a n Kodak Company and d i d n o t undergo f u r t h e r p u r i f i c a t i o n .


R e s u l t s and D i s c u s s i o n 1. C h a r a c t e r i z a t i o n o f t h e P o l y s t y r e n e L a t e x S a m p l e s , The p o l y s t y r e n e , PS, l a t e x samples under i n v e s t i g a t i o n were c h a r a c t e r ized according t o p a r t i c l e s i z e , concentration o f surface s u l p h a t e s and e l e c t r o p h o r e t i c m o b i l i t y , em, i n d e i o n i z e d w a t e r . The r e s u l t s , T a b l e I , show t h a t a l l t h e s a m p l e s w e r e o f s i m i l a r s i z e w i t h t h e e x c e p t i o n t h a t t h e Dow l a t e x e s w e r e m o n o d i s p e r s e w h i l e Ci and C5 h a d a b r o a d p a r t i c l e s i z e d i s t r i b u t i o n . The Dow a n d C^ l a t e x e s had r e l a t i v e l y l o w s u r f a c e charge d e n s i t i e s , as determined f r o m c o n d u c t o m e t r i c t i t r a t i o n , o f 3.1 and 5.9 y c / c m , r e s p e c t i v e l y , w h i l e t h e C5 l a t e x e x h i b i t e d a h i g h s u r f a c e c h a r g e d e n s i t y o f 74 y c / c m . The d e c r e a s e i n s u r f a c e c h a r g e d e n s i t y f o r C^ and C 5 , indicated i n Table I , i s a t t r i b u t e d t o p a r t i a l h y d r o l y s i s of t h e s a m p l e s w h i c h w e r e s t o r e d u n d e r room t e m p e r a t u r e c o n d i t i o n s f o r a b o u t two y e a r s . The Dow l a t e x , h o w e v e r , was i n t e n t i o n a l l y h y d r o l y z e d a t 90°C w i t h t h e r e s u l t t h a t no a c i d g r o u p s w e r e d e t e c table. A s t r i k i n g feature o f the electrophoretic m o b i l i t y results i n d e i o n i z e d w a t e r i s t h e t o t a l l a c k o f dependence on t h e concen t r a t i o n o f s u r f a c e a c i d , s u l p h a t e , g r o u p s . The i n d i c a t i o n i s that negative i o n s , the only p o s s i b i l i t y being hydroxyl i o n s , ad s o r b o n t h e h y d r o p h o b i c p a r t o f t h e PS s u r f a c e . 2. The E f f e c t o f N a C l o n t h e E l e c t r o p h o r e t i c M o b i l i t y o f PS Latex P a r t i c l e * The em o f t h e Dow 357 nm l a t e x i n t h e Η-form and N a - f o r m , a l o n g w i t h two o t h e r Dow m o n o d i s p e r s e l a t e x e s i n t h e Hf o r m w i t h d i a m e t e r s o f 795 a n d 1100 nm, w a s m e a s u r e d a s a f u n c t i o n o f NaCl c o n c e n t r a t i o n . The r e s u l t s i n F i g u r e 1 show t h a t t h e em f o r a l l t h r e e l a t e x e s i n c r e a s e d w i t h i n c r e a s i n g c o n c e n t r a t i o n o f N a C l t o a maximum a t a b o u t 1 χ ΙΟ"" M N a C l f o l l o w e d b y a r a p i d decrease. Converting the e l e c t r o p h o r e t i c m o b i l i t y t o zeta p o t e n t i a l , u s i n g t a b l e s d e r i v e d b y O t t e w i l l and Shaw ( 6 ) f r o m t h e r e s u l t s o f W i e r s m a e t a l . i n o r d e r t o a c c o u n t f o r r e l a x a t i o n and r e t a r d a t i o n e f f e c t s , l e d t o t h e same d e p e n d e n c y a s shown i n F i g u r e 2. The Η-form l a t e x was c o n v e r t e d t o N a - f o r m l a t e x b y a d d i n g e i t h e r a n e x c e s s o r a n e x a c t amount o f NaOH a s d e t e r m i n e d b y conductometric t i t r a t i o n i n order t o e l i m i n a t e t h e p o s s i b l e e f f e c t o f t h e i o n - e x c h a n g e b e t w e e n t h e Y& i o n o n t h e l a t e x p a r t i c l e and Na i o n i n the solution. The r e s u l t s showed t h a t t h e N a - f o r m l a t e x h a d t h e same em (3.2 μ.cm/sec. v o l t ) w i t h Η-form l a t e x (3.1 μ.cm/sec. v o l t ) i n d e i o n i z e d w a t e r and same i n c r e a s i n g d e p e n d e n c y o f m o b i l i t y w i t h i n c r e a s i n g N a C l c o n c e n t r a t i o n , F i g u r e 1. A reasonable explanation f o r the increase i n z e t a p o t e n t i a l i s the a d s o r p t i o n o f n e g a t i v e c h l o r i d e i o n from s o l u t i o n t o t h e s u r face of l a t e x p a r t i c l e . The d e c r e a s e i n em a b o v e 10"" M N a C l i s associated w i t h compression o f the e l e c t r i c a l double l a y e r . 2

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Zeta potential of 357-nm PS latex as a function of NaCl concentration



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3. The E l e c t r o p h o r e t i c M o b i l i t y o f t h e H y d r o x y l - f o r m 357 nm PS L a t e x . The h y d r o x y l a t e d 357 nm PS l a t e x was shown i n T a b l e I t o h a v e t h e same em i n d e i o n i z e d w a t e r a s t h e o r i g i n a l l a t e x e v e n t h o u g h no a c i d g r o u p s w e r e d e t e c t a b l e b y c o n d u c t o m e t r i c t i t r a t i o n . S i n c e t h e p r o t o n o n t h e h y d r o x y l was assumed n o t t o be d i s s o c i a b l e , t h e o r i g i n o f t h e n e g a t i v e c h a r g e was a t t r i b u t e d t o t h e a d s o r p t i o n o f a n i o n s , i n t h i s c a s e h y d r o x y l i o n s . The em o f t h i s l a t e x i n b o t h t h e h y d r o x y l - f o r m and t h e o r i g i n a l s u l p h a t e - f o r m was i n v e s t i g a t e d i n F i g u r e 3 a s a f u n c t i o n o f pH. The r e s u l t s f o r b o t h s a m p l e s a r e v e r y s i m i l a r above a pH v a l u e o f 6. When t h e l a t e x e s a r e e x p o s e d t o more a c i d i c e n v i r o n m e n t s , h o w e v e r , t h e n e g a t i v e p o t e n t i a l o f t h e h y d r o x y 1 - f o r m l a t e x d e c r e a s e s more r a p i d l y w i t h d e c r e a s i n g pH t h a n t h e o r i g i n a l l a t e x . Figure 4 shows t h e r e s u l t s f o r t h e same s a m p l e s a s a f u n c t i o n o f pH a t a constant NaCl c o n c e n t r a t i o n o f 2 χ 1 0 " % . No d i f f e r e n c e i n r e s u l t s was o b s e r v e d a t h i g h pH e x c e p t t h a t t h e em f o r b o t h s a m p l e s was h i g h e r b e l o w pH v a l u e s o f 10. F u r t h e r m o r e , when t h e pH was d e c r e a s e d b e l o w 5, t h e em d e c r e a s e d f a s t e r w i t h N a C l p r e s e n t . A l s o , t h e maximum a t pH 2.5 was e l i m i n a t e d i n t h e p r e s e n c e o f NaCl. The em f o r t h e h y d r o x y l - f o r m o f t h e l a t e x was a l s o o b s e r v e d t o d e c r e a s e f a s t e r i n t h e l o w pH r a n g e p o s s i b l y d u e t o t h e a d s o r p t i o n o f p r o t o n s on t h e s u r f a c e h y d r o x y I s . The em o f t h e h y d r o x y l - f o r m l a t e x was a l s o i n v e s t i g a t e d a s a f u n c t i o n o f t h e c o n c e n t r a t i o n o f t h e d i f f e r e n t e l e c t r o l y t e s NaOH, N a C l and HC1. The r e s u l t s i n F i g u r e 5 show t h a t t h e c h a r g e o n t h i s l a t e x i s independent o f t h e type o f e l e c t r o l y t e a t concen t r a t i o n b e l o w 10~5M. The r e s u l t s a t h i g h e r c o n c e n t r a t i o n s show t h a t h y d r o x y l i o n s a d s o r b more s t r o n g l y t h a n c h l o r i d e i o n s , and t h a t h y d r o g e n i o n s a d s o r b more s t r o n g l y t h a n s o d i u m i o n s . The same t r e n d s w e r e o b s e r v e d f o r t h i s l a t e x i n t h e s u l p h a t e f o r m . Thes^ r e s u l t s a r e c o n s i s t e n t w i t h t h e concept t h a t t h e o r i g i n o f c h a r g e on PS l a t e x e s b o t h w i t h and w i t h o u t s u r f a c e a c i d g r o u p s , i s due p r i m a r i l y t o t h e a d s o r p t i o n o f i o n s o n t o t h e h y d r o p h o b i c p a r t s of t h e s u r f a c e . Table I P a r t i c l e S i z e and S u r f a c e C h a r g e D e n s i t y o f PS L a t e x e s Electrophoretic S u r f a c e Charge Mobility i n Particle Density (sulfate Deionized Water, Latex S i z e , nm g r o u p ) , yc/cm2 μπι cm/sec v o l t Dow LS 1010 357 3.1 3.2 ( s u l f a t e form) Dow L S 1010 357 0 3.1 ( h y d r o x y l form) C 416 5.9 ( 1 1 ) * 3.7 C 448 74 ( 1 7 4 ) * 4.3 * 0 r i g i n a l r e s u l t s o b t a i n e d b y S.M. Ahmed s o o n a f t e r s a m p l e p r e paration (2). x

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Electrophoretic mobility of 357-nm PS latex as a function of PH ((Φ) sulfate form; (O) hydroxyl form)

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Electrophoretic mobility of 357-nm PS latex as a function of PH in 2 X 10' M NaCl ((Φ) sulfate form; (O) hydroxyl form) 3



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Figure 5. Electrophoretic mobility of the hydroxyl form 357-nm PS latex as a function of the concentration of electrolytes ((A) in NaOH; ([J) in NaCl; (O) in HCl)

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Figure 6.

Zeta potential of 357-nm PS latex as a function of SLS concentration



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4. The E f f e c t o f A d s o r b e d SLS o n t h e E l e c t r o p h o r e t i c M o b i l i t y o f PS L a t e x . The z e t a p o t e n t i a l , c o r r e c t e d f o r r e t a r d a t i o n and r e l a x a t i o n e f f e c t s ( 6 ) , o f t h e o r i g i n a l 3 5 7 nm PS l a t e x was d e t e r m i n e d a s a f u n c t i o n o f SLS c o n c e n t r a t i o n . The r e s u l t s i n F i g u r e 6 show t h a t t h e r e i s e s s e n t i a l l y no change i n t h e z e t a p o t e n t i a l up t o t h e CMC a f t e r w h i c h t h e z e t a p o t e n t i a l i n c r e a s e s , w h i c h i s c o n s i s t e n t w i t h r e s u l t s o b t a i n e d by Kayes ( 7 ) . S o l u t i o n a d s o r p t i o n i s o t h e r m s o n t h e same l a t e x a t d i f f e r e n t N a C l c o n c e n t r a t i o n , F i g u r e 7 , show t h a t t h e a d s o r p t i o n o c c u r s up t o t h e CMC, a f t e r w h i c h a d s o r p t i o n t e n d s t o l e v e l o f f . The f a c t i s t h a t t h e z e t a p o t e n t i a l measured under these c o n d i t i o n s i s n o t a f u n c t i o n o f t h e c o n c e n t r a t i o n o f a d s o r b e d SLS. The i n t e r p r e t a t i o n o f these r e s u l t s , which i s c o n s i s t e n t w i t h the r e s u l t s presented a b o v e , i s t h a t t h e n e g a t i v e c h a r g e o n t h e PS l a t e x s u r f a c e i n d e i o n i z e d water i s c o n t r o l l e d p r i m a r i l y by the a d s o r p t i o n o f hyd r o x y l i o n s . The i n c r e a s e i n SLS c o n c e n t r a t i o n r e s u l t s i n a d s o r p t i o n L S i o n s , p o s s i b l y t h r o u g h d i s p l a c e m e n t o f h y d r o x y l i o n s , and a decrease i n the degree o f d i s s o c i a t i o n o f the s u r f a c e sulphate groups. The i n c r e a s e i n t h e z e t a p o t e n t i a l above t h e CMC i s n o t w e l l u n d e r s t o o d a t t h i s t i m e , b u t c o u l d b e due t o t h e a d s o r p t i o n o f m i c e l l e s , w h i c h c o n c e n t r a t i o n range has been beyond t h e scope o f s o l u t i o n a d s o r p t i o n measurements. The em o f t h e 3 5 7 nm PS l a t e x was m e a s u r e d a s a f u n c t i o n o f SLS c o n c e n t r a t i o n i n t h e p r e s e n c e o f d i f f e r e n t c o n c e n t r a t i o n s o f NaCl. The r e s u l t s i n F i g u r e 8 show t h a t N a C l a f f e c t s t h e n e g a t i v e c h a r g e o f t h i s l a t e x i n a c o m p e t i t i v e f a s h i o n w i t h SLS. As the c o n c e n t r a t i o n o f NaCl i n c r e a s e s t h e n e g a t i v e charge o n t h e l a t e x s u r f a c e i n c r e a s e s , and s u b s e q u e n t a d s o r p t i o n o f SLS h a s a decreasing e f f e c t on the e x i s t i n g surface o r z e t a p o t e n t i a l . A l t h o u g h P i i r m a ( 8 ) h a s shown t h a t t h e s a t u r a t e d a d s o r p t i o n o f SLS on PS l a t e x i n c r e a s e s w i t h i n c r e a s i n g N a C l c o n c e n t r a t i o n , o u r r e s u l t s , F i g u r e 7 , show o n l y a s m a l l i n c r e a s e i n t h e a d s o r p t i o n o f SLS. The i n t e r p r e t a t i o n o f t h e r e s u l t s i n F i g u r e 8 i s t h a t t h e C I i o n a d s o r b s o n t h e h y d r o p h o b i c p a r t o f t h e PS l a t e x s u r f a c e , and t h a t LS i o n d i s p l a c e s t h e CI i o n by p r e f e r e n t i a l adsorption. As t h e adsorbed CI i o n c o n c e n t r a t i o n i n c r e a s e s , subsequent a d s o r p t i o n o f t h e LS i o n by displacement o f t h e CI i o n has a d e c r e a s i n g e f f e c t o n t h e s u r f a c e p o t e n t i a l . These r e s u l t s a l s o suggest that the decreasing order o f a d s o r p t i o n o f anions a r e L S , OH, and C I r e s p e c t i v e l y . 5. E l e c t r o p h o r e t i c M o b i l i t y o fLatexes w i t h High Concentrat i o n o f S u r f a c e S u l p h a t e G r o u p s . The two PS l a t e x e s , C^ and C 5 , were prepared w i t h i n c r e a s i n g c o n c e n t r a t i o n s o f s u l p h a t e f u n c t i o n a l monomers ( 2 ) . C o n d u c t o m e t r i c t i t r a t i o n r e s u l t s f o r a c i d g r o u p s , T a b l e I , showed t h a t t h e s u r f a c e c h a r g e d e n s i t y was 5 . 9 and 7 4 y c / c m f o r C^ and C 5 , r e s p e c t i v e l y , w h i l e t h e em i n d e i o n i z e d w a t e r was e s s e n t i a l l y i n s e n s i t i v e t o s u r f a c e charge density. The em f o r t h e s e two l a t e x e s was m e a s u r e d a s a f u n c t i o n o f NaCl c o n c e n t r a t i o n . The z e t a p o t e n t i a l c a l c u l a t e d f r o m t h e s e r e s u l t s , F i g u r e 9 , show t h a t f o r C\ t h e r e i s no c h a n g e up t o a c o n 2



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Figure 8. Electrophoretic mobility of 357-nm PS latex as a function of concentra tion of SLS in different concentrations of NaCl ((O) without NaCl; (Φ) 10~ M NaCl; (A) 10' M NaCl; Ο 10 M NaCl) 4

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c e n t r a t i o n of 1 0 " % , a f t e r which the z e t a p o t e n t i a l i n c r e a s e s t o a maximum f o l l o w e d b y a d e c r e a s e . The C 5 s a m p l e , w h i c h has a n order of magnitude h i g h e r c o n c e n t r a t i o n o f s u r f a c e a c i d groups, h o w e v e r , d e c r e a s e s l i n e a r l y w i t h i n c r e a s i n g N a C l c o n c e n t r a t i o n up t o 10""%, a f t e r w h i c h t h e z e t a p o t e n t i a l r e m a i n s c o n s t a n t . The i n t e r p r e t a t i o n o f these r e s u l t s i s that the z e t a p o t e n t i a l o f i s c o n t r o l l e d p r i m a r i l y b y t h e a d s o r p t i o n o f C I i o n s r e p l a c i n g OH i o n s on the hydrophobic p a r t o f the s u r f a c e , w h i l e the z e t a potent i a l o f C5 i s c o n t r o l l e d by the d e c r e a s i n g i o n i z a t i o n p o t e n t i a l o f t h e s u r f a c e s u l p h a t e s w i t h i n c r e a s i n g c o n c e n t r a t i o n o f Na i o n s . The em was a l s o m e a s u r e d f o r and C 5 a s a f u n c t i o n o f SLS concentration. The r e s u l t s , F i g u r e 10, show t h a t t h e z e t a p o t e n t i a l i n c r e a s e s w i t h i n c r e a s i n g SLS i n a manner s i m i l a r t o w h a t was o b t a i n e d f o r t h e 357ranPS l a t e x i n F i g u r e 8. The C 5 s a m p l e , howe v e r , d e c r e a s e d l i n e a r l y w i t h i n c r e a s i n g SLS c o n c e n t r a t i o n up t o 1 0 ~ % , f o l l o w e d b y a n i n c r e a s e above t h e CMC c o n c e n t r a t i o n . The c o n c e n t r a t i o n e f f e c t o f SLS o n t h e z e t a p o t e n t i a l o f t h e C 5 s a m p l e i s i n q u a n t i t a t i v e agreement w i t h t h e c o n c e n t r a t i o n e f f e c t o f N a C l on t h i s s a m p l e up t o 10"*%. T h e s e r e s u l t s s u g g e s t t h a t SLS d o e s not adsorb s t r o n g l y o n a l a t e x sample c o n t a i n i n g a h i g h c o n c e n t r a t i o n o f s u r f a c e s u l p h a t e s , and t h a t t h e d e c r e a s e i n z e t a p o t e n t i a l w i t h i n c r e a s i n g c o n c e n t r a t i o n o f e i t h e r N a C l o r SLS i s d u e t o t h e decrease i n the degree o f d i s s o c i a t i o n o f the s u r f a c e s u l p h a t e s w i t h i n c r e a s i n g Na i o n c o n c e n t r a t i o n . Solution adsorption i s o t h e r m s o f SLS w a s m e a s u r e d o n C^ and C 5 . The r e s u l t s o n C 5 w e r e l i m i t e d b e c a u s e o f t h e l i m i t e d amount o f s a m p l e a v a i l a b l e . The r e s u l t s , F i g u r e 11, show t h a t SLS a d s o r b s t o a much g r e a t e r e x t e n t on a s compared t o C 5 w h e r e t h e c a l c u l a t e d c r o s s s e c t i o n a l a r e a w e r e 57 and 300 Â /molecule f o r C^ and C 5 , r e s p e c t i v e l y . T h e s e r e s u l t s a r e i n agreement w i t h t h e i n t e r p r e t a t i o n o f t h e em r e s u l t s p r o p o s e d above. 2

Conclusions PS l a t e x e s a r e g e n e r a l l y p r e p a r e d b y e m u l s i o n p o l y m e r i z a t i o n u s i n g potassium persulphate as i n i t i a t o r . The c o n c e n t r a t i o n o f s u r f a c e sulphates i n these l a t e x e s are u s u a l l y i n the range o f 1 t o 5 s i t e s / 1 0 0 0 Â2. The r e s u l t s p r e s e n t e d i n t h i s p a p e r show t h a t the z e t a p o t e n t i a l i s independent o f the c o n c e n t r a t i o n o f s u r f a c e s u l p h a t e s when t h e c o n c e n t r a t i o n o f t h e s e s u r f a c e s u l p h a t e s i s r e l a t i v e l y low. T h e c o n t r o l l i n g mechanism f o r t h e g e n e r a t i o n o f s u r f a c e p o t e n t i a l i n these cases i s the tendency f o r the hydrophob i c p a r t o f t h e s u r f a c e , w h i c h r e p r e s e n t s a much g r e a t e r f r a c t i o n o f t h e s u r f a c e , t o a d s o r b n e g a t i v e i o n s . The a n i o n s w h i c h w e r e i n v e s t i g a t e d w e r e L S , OH, and C I i n t h a t o r d e r w i t h r e s p e c t t o preferential adsorption. When t h e c o n c e n t r a t i o n o f s u r f a c e s u l p h a t e s i s h i g h , i . e . g r e a t e r t h a n 15 s i t e s / 1 0 0 0 Â , t h e s u r f a c e i s h y d r o p h i l i c and t h e z e t a p o t e n t i a l i s p r e d o m i n a n t l y a f u n c t i o n o f the degree o f d i s s o c i a t i o n o f the s u r f a c e s u l p h a t e s . 2


260

AND EMULSION POLYMERIZATION


EMULSION POLYMERS

10

1

10"

10"

z

SLS C o n c e n t r â t ! o n , Γ1

Figure 10.

Zeta potential of the PS latex CI and C5 as a function of the concen tration of SLS



15.

MA ET AL.

Electrophoretic Mobility and Ion Adsorption

SLS Concentration, M

Figure 11.

Λ dsorption of SLS on PS latex Cl and C5


261

262

EMULSION POLYMERS AND EMULSION POLYMERIZATION

Literature Cited 1. 2. 3. 4. 5. Downloaded by PURDUE UNIVERSITY on June 13, 2013 | http://pubs.acs.org Publication Date: October 7, 1981 | doi: 10.1021/bk-1981-0165.ch015

6. 7. 8.

Kamel, Α., Ma, C. M., El-Aasser, M. S., Micale, F. J., Vanderhoff, J. W., presented at 54th Colloid and Surface Science Symposium, June 1980. Ahmed, S. Μ., Ph.D. thesis, Lehigh University, 1979. Vanderhoff, J. W., Van den Hul, H. J., J. Colloid Interface Sci., 1968, 28, 336. Van den Hul, H. J., and Vanderhoff, J. W., Brit. Polymer J. 1970, 2, 121. Saunders, F. L . , J. Colloid and Interface Sci., 1968, 28, 475-80. Ottewill, R. Η., and Shaw, J. N., J. Electroanal. Chem., 1972, 37, 133-42. Kayes, J. B., J. Colloid and Interface Sci., 1976, 56, 426442. Piirma, I., Chen, S. R., J. Colloid and Interface Sci., 1980, 74, 90-102.

RECEIVED

April 6, 1981.


Emulsion Polymers and Emulsion Polymerization - American

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