Polymer Adsorption at the Lower Critical Solution Temperature and Its

9 Polymer Adsorption at the Lower Critical Solution Temperature and Its Effect on Colloid Stability

Downloaded by UNIV OF PITTSBURGH on October 21, 2015 | http://pubs.acs.org Publication Date: February 10, 1984 | doi: 10.1021/bk-1984-0240.ch009

KUNIO FURUSAWA and YOSHIHIRO ΚIMURA—Department of Chemistry, The University of Tsukuba, Sakura-mura Niihari-gun, Ibaraki 305, Japan TORU TAGAWA—Mitsubishi Chemical Industries Ltd., Kamoshida-cho, Yokohama, Kanagawa 227, Japan

Adsorption behavior and the effect on colloid stability of water soluble polymers with a lower critical solution temperature(LCST) have been studied using polystyrene latices plus hydroxy propyl cellulose(HPC). Saturated adsorption(As) of HPC depended significantly on the adsorption temperature and the As obtained at the LCST was 1.5 times as large as the value at room temperature. The high As value obtained at the LCST remained for a long time at room temperature, and the dense adsorption layer formed on the latex particles showed strong protective action against salt and temperature. Furthermore, the dense adsorption layer of HPC on silica particles was very effective in the encapsulation process with polystyrene via emulsion polymerization in which the HPC-coated silica particles were used as seed. Among t h e v a r i o u s b r a n c h e s i n c o l l o i d a n d i n t e r f a c e s c i e n c e , p o l y m e r a d s o r p t i o n a n d i t s e f f e c t o n t h e c o l l o i d s t a b i l i t y i s one o f t h e most c r u c i a l p r o b l e m s . P o l y m e r m o l e c u l e s a r e i n c r e a s i n g l y u s e d a s s t a b i l i z e r s i n many i n d u s t r i a l p r e p a r a t i o n s , where s t a b i l i t y i s n e e d e d a t a h i g h d i s p e r s e d p h a s e volume f r a c t i o n , a t a h i g h e l e c t r o l y t e c o n c e n t r a t i o n , as w e l l as under extreme temper ature and f l o w v e l o c i t y c o n d i t i o n s . U n d e r s t a n d i n g how p o l y m e r f u n c t i o n s a s a s t a b i l i z e r a n d f l o c c u l a n t i s o b v i o u s l y a problem o f polymer adsorption and i t s c o n f o r m a t i o n a t t h e p a r t i c l e / l i q u i d i n t e r f a c e ( l , 2). The p r o c e s s o f p o l y m e r a d s o r p t i o n i s f a i r l y c o m p l i c a t e d ; t h e b e h a v i o r depends on many f a c t o r s , e.g., t h e n a t u r e o f t h e a d s o r b e n t , t h e m o l e c u l a r weight o f the polymer, t h e temperature, t h e e f f e c t o f t h e s o l v e n t ,

0097-6156/84/0240-0131 $06.00/0 © 1984 American Chemical Society

In Polymer Adsorption and Dispersion Stability; Goddard, E., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

POLYMER ADSORPTION AND DISPERSION STABILITY


132

etc. Among t h e s e f a c t o r s , t h e s o l v e n c y o f t h e medium l i q u i d can h a v e an i n f l u e n c e on t h e a d s o r p t i o n i n two ways (50 . One i s t h e e n e r g e t i c f a c t o r , i . e . , s i n c e a p o l y m e r m o l e c u l e must r e p l a c e s o l v e n t m o l e c u l e s t o he a d s o r b e d , t h e d i f f e r e n c e i n e n e r g y o f i n t e r a c t i o n b e t w e e n a d s o r b e n t and s o l v e n t , and a d s o r b e n t and p o l y m e r moleculet w i l l be i m p o r t a n t i n d e t e r m i n i n g t h e e x t e n t o f a d s o r p t i o n . A n o t h e r i s t h e r e l a t i v e i n t e r a c t i o n o f p o l y m e r - s o l v e n t and s o l v e n t s o l v e n t , which leads t o the e x p e c t a t i o n t h a t a d s o r p t i o n i s best from a poor s o l v e n t . Apart from e n e r g e t i c reasons, the t i g h t e r c o i l i n g o f the polymers i n the poorer s o l v e n t would i n c r e a s e the amount o f p o l y m e r t h a t c o u l d f i t i n t o a g i v e n a r e a o f an a d s o r b e n t s u r f a c e . The r i s e i n a d s o r p t i o n i n r e v e r s e o r d e r t o s o l v e n t power has b e e n c o n f i r m e d by many r e s e a r c h e r s (J+, 5.). According t o t h i s concept, i t i s expected t h a t polymer mole c u l e s , e s p e c i a l l y h i g h m o l e c u l a r w e i g h t p o l y m e r s , g i v e an i n c r e a s e d a d s o r p t i o n a t a t e m p e r a t u r e c l o s e t o t h e c l o u d p o i n t , and p a r t i c l e s w i t h t h e t h i c k ( o r dense) a d s o r p t i o n l a y e r o f polymer formed out o f a p o o r s o l v e n t w o u l d show s t r o n g p r o t e c t i o n a g a i n s t f l o c c u l a t i o n . In t h i s study, a d s o r p t i o n behavior o f water s o l u b l e polymers and t h e i r e f f e c t on c o l l o i d s t a b i l i t y have b e e n s t u d i e d u s i n g p o l y s t y r e n e l a t i c e s p l u s c e l l u l o s e d e r i v a t i v e s . As t h e aqueous s o l u t i o n o f h y d r o x y p r o p y l c e l l u l o s e ( H P C ) has a l o w e r c r i t i c a l s o l u t i o n t e m p e r a t u r e ( L C S T ) , n e a r 50 °C(6), an i n c r e a s e d a d s o r p t i o n and s t r o n g p r o t e c t i o n can be e x p e c t e d b y t r e a t i n g t h e l a t i c e s w i t h HPC a t t h e LCST. A l s o , h e r e , t h e e f f e c t o f t h e a d s o r p t i o n l a y e r o f HPC on e n capsulation of s i l i c a p a r t i c l e s i n polymerization of styrene i n t h e p r e s e n c e o f s i l i c a p a r t i c l e s has b e e n i n v e s t i g a t e d . E n c a p s u l a t i o n i s p r o m o t e d g r e a t l y by t h e e x i s t e n c e o f t h e a d s o r p t i o n l a y e r on t h e s i l i c a p a r t i c l e s , and t h e dense a d s o r p t i o n l a y e r f o r m e d a t t h e LCST makes c o m p o s i t e p o l y s t y r e n e l a t i c e s w i t h s i l i c a p a r t i c l e s i n t h e core(7_). T h i s type o f examination i s e n t i r e l y new i n p o l y m e r a d s o r p t i o n s t u d i e s and we b e l i e v e t h a t t h i s work w i l l c o n t r i b u t e n o t o n l y t o new c o l l o i d a n d i n t e r f a c e s c i e n c e , but a l s o to i n d u s t r i a l technology. Experimental Materials P o l y s t y r e n e l a t i c e s u s e d as an a d s o r b e n t were p r e p a r e d by t h e Kotera-Furusawa-Takeda method(8j t o reduce the spurious e f f e c t s o f surface a c t i v e substances. The a v e r a g e d i a m e t e r ( D ) and t h e s u r f a c e g h a r g e density(σο) o f t h e l a t e x p a r t i c l e s w e r e d e t e r m i n e d : D = 2 0 0 0 A and σ = 1.5 uC/cm . A s i l i c a sample was p r e p a r e d b y t h e m e t h o d d e s c r i b e d by S t 8 b e r e t a l . ( £ ) , and was composed o f h i g h l y monod i s p e r s e s p h e r i c a l p a r t i c l e s o f 1900 X i n d i a m e t e r . These c o l l o i d s were u s e d a f t e r d i a l y z i n g e x h a u s t i v e l y a g a i n s t d i s t i l l e d w a t e r t o remove t h e i o n i c i m p u r i t i e s . The c e l l u l o s e d e r i v a t i v e s u s e d were o b t a i n e d by t h e f r a c t i o n a l p r e c i p i t a t i o n method w i t h t h e use o f e t h a n o l as s o l v e n t and n2

0



9.

FURUSAWA ET AL.

Polymer Adsorption

at LCST and Colloid Stability

133

h e p t a n e a s a p r e c i p i t a n t a t 30 °C. The HPC, f r o m N i p p o n Soda I n d u s t r i e s Co., J a p a n , a n d h y d r o x y e t h y l c e l l u l o s e ( H E C ) , f r o m H e r c u l e s Co., The N e t h e r l a n d s , u s e d i n t h i s s t u d y have a d e g r e e o f e t h e r s u b s t i t u t i o n o f 2 Λ a n d 2.5 on e a c h monomer u n i t , r e s p e c t i v e l y . The m o l e c u l a r w e i g h t o f t h e s e p o l y m e r s was d e t e r mined from t h e i n t r i n s i c v i s c o s i t y - m o l e c u l a r weight r e l a t i o n s h i p . The v i s c o s i t y measurements were c a r r i e d o u t b y means o f a Ubbelohde v i s c o m e t e r a t 25 °C i n a 0.1 M o l N a C l aqueous s o l u t i o n f o r HPC(10) a n d i n d i s t i l l e d w a t e r f o r HEC(11). The m o l e c u l a r w e i g h t d i s t r i b u t i o n o f HPC-samples was a l s o a n a l y z e d b y t h e G e l P e r m e a t i o n Chromatography t e c h n i q u e . The measurements were c a r r i e d o u t w i t h a Toyosoda-HLC-Model-802 a t 25 °C w i t h a 0.1 M o l p o t a s s i u m b i phosphate b u f f e r s o l u t i o n as t h e e l u e n t . P o l y v i n y l a l c o h o l ( P V A ) was o b t a i n e d f r o m t h e K u r a r e y C o . , L t d . J a p a n ; t h e m o l e c u l a r w e i g h t a n d t h e d e g r e e o f h y d r o l y s i s were d e t e r m i n e d b y t h e s u p p l i e r a s 88,000 a n d 80 % r e s p e c t i v e l y . The molecular weight and t h e molecular weight d i s t r i b u t i o n data o f t h e p o l y m e r samples a r e shown i n T a b l e 1. 9

T a b l e 1.

M o l e c u l a r W e i g h t C h a r a c t e r i z a t i o n o f P o l y m e r Sample

Sample

Mw/M

Mw

HPC-L HPC-M HPC-H

5.3 χ 30.3 χ 92.5 χ

HEC-L HEC-H

1 3 . 0 χ 10^ 6 3 . 0 χ 10

2.76

10^ k

10

k

8.8 χ

PVA

k

10

1.8u 2.1+9

-

n

Degree o f hydrolysis

-

Degree o f e t h e r substitution/monomer

2.1* 2.1* 2.1*

—

2.5 2.5

80 %

-

The o t h e r r e a g e n t s , c o m m e r c i a l l y a v a i l a b l e , were o f a n a l y t i c a l g r a d e . A l l t h e s o l u t i o n s o f t h e s e m a t e r i a l s were made w i t h d e i o n i z e d a n d d i s t i l l e d w a t e r , u s i n g an a l l - P y r e x a p p a r a t u s . Phase S e p a r a t i o n Measurements The measurements were c a r r i e d o u t w h i l e i n c r e a s i n g t h e t e m p e r a t u r e i n 0 . 5 °C i n c r e m e n t s a t i n t e r v a l s o f 30 m i n . , u s i n g an aqueous s o l u t i o n o f t h e p o l y m e r s i n P y r e x t u b e s ( 5 m l v o l u m e ) . E a c h t u b e c o n t a i n e d a s h o r t g l a s s r o d w h i c h was u s e d t o s t i r t h e s o l u t i o n ; a f t e r b e i n g f i l l e d w i t h t h e polymer s o l u t i o n o f 0.05 2 . 5 wt % e a c h t u b e was e v a c u a t e d a n d s e a l e d . The warm up t o 70 °C was c a r r i e d o u t i n a w a t e r b a t h . The c l o u d p o i n t was t a k e n as t h e t e m p e r a t u r e a t w h i c h phase s e p a r a t i o n was f i r s t n o t e d ; i t was compared w i t h t h e t e m p e r a t u r e a t w h i c h t h e s o l u t i o n f i r s t became c l e a r a g a i n w h i l e c o o l i n g . 9



134


A d s o r p t i o n Measurements The amounts o r a d s o r p t i o n o f t h e p o l y m e r on l a t e x and s i l i c a p a r t i c l e s were m e a s u r e d as f o l l o w s . Three m i l l i l i t e r s o f t h e p o l y m e r s o l u t i o n c o n t a i n i n g a known c o n c e n t r a t i o n was i n t r o d u c e d i n t o an a d s o r p t i o n t u b e ( 1 0 m l volume) w h i c h c o n t a i n e d 2 ml o f l a t e x (C = h.O wt %) a n d s i l i c a ( C = 2.0 wt %) s u s p e n s i o n s . A f t e r b e i n g r o t a t e d ( l 0 rpm) e n d - o v e r - e n d f o r 1 h r i n a w a t e r b a t h a t a c o n s t a n t t e m p e r a t u r e , t h e c o l l o i d p a r t i c l e s were s e p a r a t e d f r o m t h e s o l u t i o n b y c e n t r i f u g a t i o n ( 2 5 0 0 0 G, 30 min.) u n d e r a c o n t r o l l e d t e m p e r a t u r e . The p o l y m e r c o n c e n t r a t i o n t h a t r e m a i n e d i n t h e s u p e r n a t a n t was m e a s u r e d c o l o r i m e t r i c a l l y , u s i n g s u l f u r i c a c i d and p h e n o l f o r t h e c e l l u l o s e d e r i v a t i v e s ( 1 2 ) , a n d p o t a s s i u m i o d i d e , i o d i n e and b o r i c a c i d f o r PVA(13). From t h e s e m e a s u r e m e n t s , t h e number o f m i l l i grams o f a d s o r b e d p o l y m e r p e r s q u a r e m e t e r o f t h e a d s o r b e n t s u r f a c e was c a l c u l a t e d u s i n g a c a l i b r a t i o n c u r v e . F l o c c u l a t i o n Experiments I n g l a s s - s t o p p e r e d v i a l s ( 8 ml v o l u m e ) , 5 ml p o r t i o n s o f MgCl2 s o l u t i o n o f v a r i o u s c o n c e n t r a t i o n s were t a k e n and on t o p o f t h e s a l t s o l u t i o n , 2 ml o f the suspension o f polymer-coated p a r t i c l e s , w h i c h were p r e p a r e d by a d s o r b i n g a p o l y m e r a t a c o n t r o l l e d t e m p e r a t u r e , w e r e a d d e d c a r e f u l l y i n s u c h a way t h a t a s h a r p b o u n d a r y b e t w e e n t h e d i s p e r s i o n a n d t h e s a l t s o l u t i o n was f o r m e d . After b e i n g r o t a t e d e n d - o v e r - e n d ( l 0 rpm) f o r 2 h r s , t h e sample was l e f t t o s t a n d f o r 10 h r s i n o r d e r t o a l l o w t h e f l o c c u l a t e d p a r t i c l e s t o settle. T h e n , t h e e x t i n c t i o n o f t h e s u p e r n a t a n t was m e a s u r e d u s i n g a Jasco D i g i t a l Spectrophotometer(Uvidec-UlO) at a wavelength o f 550 nm. The c r i t i c a l f l o c c u l a t i o n c one e nt r a t i o n ( C F C ) was d e f i n e d as t h e s a l t c o n c e n t r a t i o n a t w h i c h t h e a b s o r b a n c e o f t h e s u p e r n a t a n t was r e d u c e d t o 50 % o f t h e o r i g i n a l . The i o n i c s t r e n g t h was v a r i e d u s i n g M g C l 2 , w h i l e a l l t h e e x p e r i m e n t s were c a r r i e d o u t a t a c o n s t a n t t e m p e r a t u r e o f 25 °C. As a n o t h e r c r i t e r i o n o f s t a b i l i t y , a c r i t i c a l f l o c c u l a t i o n t e m p e r a t u r e ( C F T ) was m e a s u r e d . The measurement o f CFT was c a r r i e d o u t as f o l l o w s : t h e b a r e l a t e x s u s p e n s i o n was m i x e d w i t h t h e p o l y m e r s o l u t i o n o f v a r i o u s c o n c e n t r a t i o n s a t kQ °C b y t h e same p r o c e d u r e as i n t h e a d s o r p t i o n e x p e r i m e n t s . T h e n , t h e m i x t u r e i n a P y r e x t u b e ( 8 m l , U.O wt %) was warmed s l o w l y i n a w a t e r b a t h and t h e c r i t i c a l t e m p e r a t u r e a t w h i c h t h e d i s p e r s i o n becomes s u d d e n l y c l o u d y was m e a s u r e d w i t h t h e n a k e d e y e . P o l y m e r i ζation i n t h e P r e s e n c e o f S i l i c a P a r t i c l e s R a d i c a l p o l y m e r i ζ a t i o n o f s t y r e n e was c a r r i e d o u t i n t h e presence o f bare s i l i c a p a r t i c l e s , and o f t h e HPC-coated s i l i c a p a r t i c l e s i n w a t e r b y u s i n g p o t a s s i u m p e r s u l f a t e as an i n i t i a t o r . Table 2 g i v e s t h e t y p i c a l i n g r e d i e n t s used f o r these p o l y m e r i z a tions. The H P C - c o a t e d s i l i c a p a r t i c l e s w e r e p r e p a r e d u n d e r t h e same c o n d i t i o n s as i n t h e a d s o r p t i o n e x p e r i m e n t s . The p o l y m e r i z a t i o n t e m p e r a t u r e was k e p t a t 1+5 °C t o p r o t e c t t h e a d s o r p t i o n l a y e r o f HPC, and p o l y m e r i z e d f o r 2k h r s i n t h e same manner as t h a t


9.

FURUSAWA ET AL.

Table 2 .

Polymer Adsorption


135

T y p i c a l Ingredients used f o r P o l y m e r i z a t i o n o f Styrene i n the Presence o f S i l i c a p a r t i c l e s

Samples

HPL(-) HPL(HPC) SL

Bare s i l i c a p a r t i c l e s ( w t %)

HPC-coated s i l i c a S t y r e n e (mol/l) p a r t i c l e s ( w t %)

0.2

-

O.I85

-

0.83 0.83 0.83

K2S2O8

(mol/l) 3.5x10-3 3.5xl0" 3.5x10" 3

3


P o l y m e r i z a t i o n t e m p e r a t u r e : U5 °C; P o l y m e r i z a t i o n t i m e : 2k h r s d e s c r i b e d p r e v i o u s l y ( J ) · The d e g r e e o f e n c a p s u l a t i o n o f t h e s e p a r t i c l e s was e x a m i n e d b y c o m p a r i n g t h e e l e c t r o n m i c r o g r a p h o f t h e produced p a r t i c l e s and by a n a l y z i n g t h e m o l e c u l a r weight d i s t r i b u t i o n o f t h e l a t e x polymers u t i l i z i n g G e l P e r m e a t i o n Chromatography. Results and D i s c u s s i o n Phase Diagram o f P o l y m e r - w a t e r Systems The p h a s e d i a g r a m s w h i c h were o b t a i n e d f o r t h e aqueous s o l u t i o n s o f HPC a n d PVA s a m p l e s a r e shown i n F i g . l . ( i n t h e case o f t h e HEC s a m p l e , t h e c l o u d p o i n t was n o t f o u n d i n t h e t e m p e r a t u r e r a n g e


136



e x a m i n e d ) . A l l t h e s y s t e m s show a l o w e r c r i t i c a l s o l u t i o n t e m p e r a t u r e (LCST) i n t h e 35 - 55 °C r a n g e , t h a t i s , t h e p h a s e s e p a r a t i o n o c c u r s a t a d e f i n i t e t e m p e r a t u r e on w a r m i n g , and t h e s y s t e m s become homogeneous a g a i n on c o o l i n g . I t a p p e a r s t h a t t h e LCST i s i n f l u e n c e d e x t e n s i v e l y b o t h b y t h e p o l y m e r c o n c e n t r a t i o n , and b y i t s m o l e c u l a r w e i g h t , i . e . , t h e LCST becomes l o w e r b o t h b y an increase i n t h e c o n c e n t r a t i o n and i n t h e m o l e c u l a r w e i g h t o f t h e p o l y m e r . These phenomena may be e x p l a i n e d b y t h e c o n c e p t o f t h e F l o r y ^ S c h u l z t h e o r y ( i k ) f o r t h e c r i t i c a l s o l u t i o n phenomenon. Adsorption Behavior F i g u r e 2 shows a d s o r p t i o n i s o t h e r m s o f HPC, HEC a n d PVA p o l y mers on t h e l a t i c e s a t a t e m p e r a t u r e o f k& °C. I t i s evident that t h e i s o t h e r m f o r HPC i s o f t h e h i g h a f f i n i t y t y p e , w i t h a w e l l d e f i n e d p l a t e a u . W h i l e t h e i s o t h e r m s f o r HEC and PVA a r e n o t h i g h a f f i n i t y , t h e i r p l a t e a u s a r e i n f l u e n c e d by t h e p o l y m e r c o n c e n t r a t i o n s o v e r a w i d e r a n g e . The t e m p e r a t u r e dependence o f t h e s a t u r a t e d a d s o r p t i o n ( A s ) o f t h e s e p o l y m e r s i s shown i n F i g s . 3 and k f o r t h e p o l y s t y r e n e l a t e x p a r t i c l e s , and i n F i g . 5 f o r t h e s i l i c a p a r t i c l e s . The t e m p e r a t u r e dependence f o r t h e H P C - l a t e x s y s t e m s i s shown i n Fig.3 f o r three molecular weights. A f t e r a constant value, there i s a s h a r p i n c r e a s e i n t h e As v a l u e s f o r b o t h HPC a n d PVA. The t e m p e r a t u r e dependence o f t h e As i s e s p e c i a l l y r e m a r k a b l e i n t h e HPC sample w i t h a h i g h m o l e c u l a r w e i g h t , where t h e As o f o f HPC-H a t U8 °C i s 1.5 t i m e s as l a r g e as t h e v a l u e a t 30 °C. With the H E C - l a t e x s y s t e m s , h o w e v e r , no d e f i n i t e t e m p e r a t u r e t r e n d c o u l d be d e t e c t e d . M o r e o v e r , i t seems t h a t t h e r e i s a s l i g h t d e c r e a s e i n t h e As v s . t e m p e r a t u r e c u r v e f o r HEC a d s o r p t i o n on t h e s i l i c a particles. From a c o m p a r i s o n w i t h t h e p h a s e d i a g r a m shown i n F i g . 1 , i t i s e v i d e n t t h a t t h e t r e n d s i n t h e As s e e n i n F i g s .3 - 5 a r e b a s e d on t h e s o l v e n c y o f t h e medium, i . e . r e d u c t i o n i n t h e s o l v e n c y l e a d s t o an i n c r e a s e d a d s o r p t i o n a t t h e s o l i d / w a t e r i n t e r f a c e . F u r t h e r m o r e , i t a p p e a r s t h a t t h e t e m p e r a t u r e dependence o f t h e As i s a l s o i n f l u e n c e d by t h e a d s o r b e n t , i . e . t h e dependence i s more e x t e n s i v e i n the p o l y m e r - s i l i e a p a r t i c l e system than i n the p o l y m e r - l a t e x p a r t i c l e s y s t e m . T h i s i n d i c a t e s t h a t some e n e r g e t i c f a c t o r s ( h y d r o phobic i n t e r a c t i o n , e l e c t r o s t a t i c i n t e r a c t i o n , etc.,) are a l s o p l a y i n g a r o l e t o some e x t e n t i n d e t e r m i n i n g t h e a d s o r p t i o n amounts. I t i s g e n e r a l l y accepted t h a t the time r e q u i r e d f o r desorption o f a d s o r b e d p o l y m e r i s v e r y l o n g , and t h i s p r o c e s s seems t o a p p e a r t o be i r r e v e r s i b l e ( 1 5 ) . A c c o r d i n g l y , i t i s e x p e c t e d t h a t t h e h i g h a d s o r p t i o n v a l u e s w h i c h a p p e a r e d n e a r t h e LCST may be h e l d f o r a l o n g t i m e u n d e r d i f f e r e n t t e m p e r a t u r e c o n d i t i o n s . I n T a b l e 3, e x p e r i m e n t a l r e s u l t s f o r i r r e v e r s i b i l i t y o f a d s o r p t i o n i n t h e HPCl a t e x s y s t e m s a r e shown. A f t e r t h e HPC s a m p l e s and t h e l a t e x p a r t i c l e s were m i x e d f o r 2 h r s a t U8 °C u n d e r t h e same c o n d i t i o n as i n t h e c a s e o f t h e a d s o r p t i o n p r o c e s s , one p o r t i o n o f one o f t h e s a m p l e s was s e p a r a t e d i m m e d i a t e l y b y c e n t r i f u g a t i o n a t kB °C. The o t h e r h a l f p o r t i o n o f t h e H P C - c o a t e d l a t e x s u s p e n s i o n was k e p t a t room t e m p e r a t u r e f o r k& h r s and t h e n c e n t r i f u g e d a t 6 °C. As



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FtJRUSAWA ET AL.

Polymer Adsorption


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