Ellipsometric Study of Adsorption of Polyelectrolyte onto a Metal

Jul 23, 2009 - The plateau adsorbances at constant molecular weight increased linearly with the square root of NaCl concentration. For the same NaCl ...
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3 Ellipsometric Study of Adsorption of Polyelectrolyte onto a Metal Surface

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A. TAKAHASHI, M. KAWAGUCHI, K. HAYASHI, and Τ. ΚΑΤΟ Department of Industrial Chemistry, Faculty of Engineering, Mie University, Tsu, Mie 514, Japan Adsorption of sodium poly(styrenesulfonate) from aqueous NaCl solutions onto a platinum plate at 25 °C was studied by ellipsometry as functions of molecular weight and concentration of NaCl. The plateau adsorbances at constant molecular weight increased linearly with the square root of NaCl concentration. For the same NaCl concentra­ tion the adsorbance was nearly independent of the molecular weight. The thickness of the adsorbed layer was approximately proportional to the square root of the molecular weight for the Theta solvent (4.17 M NaCl). For good solvents of lower NaCl concentrations the exponent of the molecular weight dependence of the thickness was less than 0.5. At the same adsorbance and molecular weight the cube of the expansion factor α , defined by the ratio of the thicknesses for good solvent and for Theta solvent, was proportional to the inverse square root of NaCl concentration. t

Adsorption o f p o l y e l e c t r o l y t e on i n t e r f a c e s i s concerned with various a p p l i c a t i o n s such as f l o c c u l a t i o n and s t e r i c s t a b i l i z a t i o n of c o l l o i d a l p a r t i c l e s i n an aqueous phase, o i l recovery, and s o i l c o n d i t i o n i n g . In these cases, both the adsorbance o f ρ οlyele c trοly tes and the conformation o f the adsorbed polymer, which i s connected w i t h the thickness o f the adsorbed l a y e r , are very important. Features of p o l y e l e c t r o l y t e adsorption are that both the adsorbance and the thickness can be e a s i l y v a r i e d by changing the concentration o f added s a l t as w e l l as pH i n bulk s o l u t i o n s i n c e such changes cause v a r i a t i o n o f the e l e c t r o s t a t i c r e p u l s i o n s o f p o l y e l e c t r o l y t e chains adsorbed, i . e . , the excluded volume e f f e c t .

0097 6156/ 84/0240 (K)39$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

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40

Hesselink attempted to c a l c u l a t e t h e o r e t i c a l adsorption isotherms f o r f l e x i b l e p o l y e l e c t r o l y t e chains using one t r a i n and one t a i l conformation (1) and l o o p - t r a i n conformation (2) as f u n c t i o n s of the s u r f a c e charge, p o l y i o n charge d e n s i t y , i o n i c s t r e n g t h , as w e l l as molecular weight. His t h e o r e t i c a l treatment l e d to extensive conclusions, which can be compared with the r e l e v a n t experimental data. Experimental s t u d i e s of the adsorption of p o l y e l e c t r o l y t e have been reported by s e v e r a l authors; P e f f e r k o r n , Dejardin, and Varoqui (_3) measured the hydro dynamic thickness of an a l t e r n a t i n g copolymer of maleic a c i d and e t h y l v i n y l ether adsorbed on the pore w a l l s i n c e l l u l o s e e s t e r f i l t e r as a f u n c t i o n of the molecular weight and the concentration of NaCl. Robb e t a l . (4) s t u d i e d the adsorption of carboxy methyl c e l l u l o s e and poly ( a c r y l i c acid) onto surfaces of i n s o l u b l e i n o r g a n i c s a l t s . However, t h e i r s t u d i e s are l i m i t e d to the measurements of adsorbance and the f r a c t i o n of adsorbed segments. For homopolyelectrolyte, we f i r s t s t u d i e d the e l l i p s o m e t r i c measurement of the adsorption of sodium p o l y ( a e r y l a t e ) onto a platinum p l a t e as a f u n c t i o n of added sodium bromide concentrat i o n C5). We measured the e f f e c t o f e l e c t r o l y t e on the thickness of the adsorbed l a y e r and the adsorbances of the p o l y e l e c t r o l y t e . I t was assumed that the Donnan e q u i l i b r i u m e x i s t e d between the adsorbed l a y e r and the bulk phase. The thickness was l a r g e r and the adsorbance o f the p o l y e l e c t r o l y t e was lower f o r the lower s a l t concentration. However, the data on the molecular weight dependence of both the adsorbance and the thickness of the adsorbed p o l y e l e c t r o l y t e have been l a c k i n g compared with the s t u d i e s of adsorption of n o n i o n i c polymers onto metal surfaces (6-9). The aim of t h i s paper i s to o f f e r experimental r e s u l t s f o r the molecular weight dependence of adsorption of p o l y ( s t y r e n e s u l f o n a t e ) onto a platinum p l a t e from aqueous NaCl s o l u t i o n at 25 °C. Measurements of p o l y ( s t y r e n e s u l f o n a t e ) adsorption were c a r r i e d out by e l l i p s o m e t r y . The dependences of molecular weight and added s a l t concentration on the thickness of the adsorbed l a y e r and a l s o the adsorbances of polymer and s a l t are examined. Experimental Materials. Four samples of sodium p o l y ( s t y r e n e s u l f o n a t e ) (NaPSS) prepared by s u l f o n a t i o n of polystyrenes with narrow molecular weight d i s t r i b u t i o n were purchased from Pressure Chemical Co. The c h a r a c t e r i s t i c s o f the samples, according to the manufacturer, are l i s t e d i n Table I. The i n t r i n s i c v i s c o s i t i e s of NaPSS i n aqueous NaCl s o l u t i o n were measured using an Ubbelhode viscometer at 25 °C. Water was twice d i s t i l l e d using an a l l Pyrex apparatus. A n a l y t i c a l grade NaCl was used without f u r t h e r p u r i f i c a t i o n .

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

3.

T A K A H A S H I ET AL.

Polyelectrolyte Adsorption

41

onto Metal

The platinum p l a t e ( I s h i f u k u Metal Co. Japan) was cleaned by soaking i n a hot concentrated aqueous HNO3-H2SO4 (1:1) mixture, washed thoroughly with d i s t i l l e d water, and then d r i e d i n a dust free box.

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Table I .

Sample

NaPSS-1 NaPSS-2 NaPSS-3 NaPSS-4

C h a r a c t e r i s t i c s of Sodium Poly(styrenesulfonates)

Μ χ 10

-1

Degree of Sulfonation 0.89 0.81 0.99 0.92

88 177 354 1060

Ellipsometry. Adsorption measurements were performed with a Shimadzu P-10 Type e l l i p s o m e t e r at 25 °C. The l i g h t source was a Nihon Denchi SH-85 Type h i g h pressure mercury lamp. The wavelength of the i n c i d e n t l i g h t was 546 nm and i n c i d e n t angle was 70 . B a s i c data of the thickness of the adsorbed l a y e r , t , and the r e f r a c t i v e index, n^, of the adsorbed l a y e r were c a l c u l a t e d from the experimental data of the phase d i f f e r e n c e , Δ , and the azimuth angle, ψ, of the amplitude r a t i o by computer. The computer program proposed by McCrackin (10) was used. Since the components i n the adsorbed p o l y e l e c t r o l y t e l a y e r are considered to be the same as the bulk phase w i t h a three component system which c o n s i s t s of p o l y e l e c t r o l y t e , simple s a l t , and water, we c a l c u l a t e the adsorbances of p o l y e l e c t r o l y t e and s a l t by assuming the Donnan e q u i l i b r i u m between the bulk phase and the adsorbed p o l y e l e c t r o l y t e l a y e r , as described p r e v i o u s l y (5). To determine the adsorbances of p o l y e l e c t r o l y t e and s a l t , the f o l l o w i n g r e l a t i o n s h i p s are used 0

R - (n

2 f

- 1) M / ( n

2 f

+ 2) d

(1)

where R i s the mean molar r e f r a c t i v i t y , M the mean molecular weight, and d the density of the adsorbed l a y e r . R and M are given by R = Z(X.R.) i i

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

(2)

42

POLYMER ADSORPTION AND DISPERSION STABILITY Μ = Σ(Χ.Μ )

(3)

±

where denotes the mole f r a c t i o n of component i . d i s expressed by

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d = d

+ (M

ο

- d V . ^ c / l O O O + (M ο + +

+

The d e n s i t y ,

- d V °)C /1000 _ o _ _

+ (M - d V °)C /1000 (4) Ρ ο ρ ρ where d i s the density of water, V ° , V _ ° , and V ° are the apparent molar volumes, M , WL, and M the molecular weights, and Of, C_, and C the molar concentrations of c a t i o n , anion, and polyion, respectively. The Donnan e q u i l i b r i u m gives Q

+

+

p

C

s

0 ( C

s

O + v

[C

V p ° > = s°

(r

+

s

+ ^ r

p

/ t ) ]

(C ° + r /t) s

(5)

s

where C ° and C ° are the molar concentrations of u n i - u n i v a l e n t s a l t and p o l y e l e c t r o l y t e i n the bulk phase, r e s p e c t i v e l y , ν i s the number of charges per p o l y i o n , φ and φ are the osmotic c o e f f i c i e n t s f o r the s a l t - f r e e bulk p o l y e l e c t r o l y t e phase and the adsorbed l a y e r , and Γ and r are the adsorbances of poly­ e l e c t r o l y t e and simple s a l t expressed i n mol/cm . Equation 5 was f i r s t d e r i v e d by Frommer and M i l l e r (11) assuming the a d d i t i v i t y r u l e f o r the osmotic f a c t o r s . From the measured r e f r a c t i v e i n d i c e s and d e n s i t i e s f o r NaPSS i n aqueous NaCl s o l u t i o n the molar r e f r a c t i v i t i e s and the apparent molar i o n volumes were c a l c u l a t e d . The f o l l o w i n g values were obtained; R ^ = 9.23 cm /mol, R ^ O 3.73 cmvfymol, s

p

ρ

ρ

g

3

=

N a C

R

NaPSS

=

71.23

3

cm /mol, V °

N a

+ = - 1.55

3

3

cm /mol, V °

c l

~ =

18.3

3

cm /mol, and V ° = 127.81 cm /mol. With φ = φ = 0.17, which was reported p r e v i o u s l y ( 12) , and the measurecf values of f » p°» ^ C ° , Γ and T were c a l c u l a t e d by s o l v i n g Equations 1, 2, 3, 4, End 5. N a P S S

n

t y

C

ρ

3 1 1

s

Q

Results Adsorption K i n e t i c s . Figure 1 shows the adsorbance, Ap, of NaPSS-3 as a f u n c t i o n of adsorption time f o r two NaCl concentrations a t the NaPSS concentration of 0.04 g/100ml. The Ap f i r s t i n c r e a s e s with adsorption time and then the e q u i l i b r i u m adsorbance i s a t t a i n e d a f t e r 1.5 χ 10 minutes. The t h i c k n e s s , t, o f the adsorbed l a y e r f o r NaPSS-3 i s p l o t t e d against adsorption time as shown i n Figure 2. The t a l s o increases with i n c r e a s i n g adsorption time and becomes a constant value. S i m i l a r time dependence was obtained i n the other experiments. Therefore, both Ap and t determined a f t e r 1.5 χ 103 minutes were taken as the e q u i l i b r i u m values.

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

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TAKAHASHI ET AL.

Polyelectrolyte Adsorption

onto Metal

Adsorption Time χ 10" (min) F i g u r e 1. A d s o r b a n c e , A , o f NaPSS-3 a s a f u n c t i o n o f a d s o r p t i o n t i m e : Ο , NaPSS c o n c e n t r a t i o n , C = 0.04 g/100ml, N a C l c o n c e n t r a t i o n , C ° = 4.17 Μ; φ , C = 0.04 g/100ml, r» O — A c iur s

Adsorption Time χ 10" (min) F i g u r e 2. T h i c k n e s s , t , o f t h e a d s o r b e d l a y e r f o r NaPSS-3 as a f u n c t i o n o f a d s o r p t i o n t i m e . S y m b o l s a r e t h e same as i n F i g u r e 1.

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

44

POLYMER ADSORPTION AND DISPERSION STABILITY

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I n F i g u r e s 3 and 4, p l o t s o f Ap and t a g a i n s t the s q u a r e r o o t o f a d s o r p t i o n t i m e , T, a r e d i s p l a y e d , r e s p e c t i v e l y . Before attainment of adsorption e q u i l i b r i u m both p l o t s are l i n e a r w i t h i n e x p e r i m e n t a l e r r o r and t h e r e f o r e , a d s o r p t i o n p r o c e s s o f NaPSS i s g o v e r n e d by d i f f u s i o n . Adsorption Isotherm. T y p i c a l adsorption isotherms f o r NaPSS-3 i n v a r i o u s N a C l c o n c e n t r a t i o n s a r e i l l u s t r a t e d i n F i g u r e 5. The a d s o r b a n c e , Ap, o f NaPSS f i r s t r i s e s w i t h NaPSS c o n c e n t r a t i o n and l e v e l s o f f t o a p l a t e a u v a l u e . The Ap v a l u e above t h e NaPSS c o n c e n t r a t i o n o f 0.04 g/100ml i s w e l l i n t h e p l a t e a u and i n c r e a s e s w i t h t h e N a C l c o n c e n t r a t i o n . The a d s o r b a n c e , Ag, o f N a C l i s negative, i t s a b s o l u t e v a l u e i n c r e a s e s w i t h t h e NaPSS c o n c e n t r a t i o n , and r e a c h e s a c o n s t a n t v a l u e above t h e NaPSS c o n c e n t r a t i o n o f 0.04 g/100ml f o r r e s p e c t i v e N a C l c o n c e n t r a t i o n s as shown i n F i g u r e 6. The p l a t e a u v a l u e o f Ag d e 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 . The t h i c k n e s s , t , o f t h e a d s o r b e d l a y e r i n c r e a s e s w i t h NaPSS c o n c e n t r a t i o n and becomes c o n s t a n t above 0.04 g/100ml f o r r e s p e c t i v e N a C l c o n c e n t r a t i o n s as i l l u s t r a t e d i n F i g u r e 7. The t i n the p l a t e a u rose w i t h d e c r e a s i n g NaCl c o n c e n t r a t i o n . S i m i l a r i s o t h e r m s f o r Ap, A , and t v a l u e s w e r e o b s e r v e d f o r t h e o t h e r samples. The p l a t e a u i s e s t a b l i s h e d a t t h e NaPSS c o n c e n t r a t i o n o f 0.04 g/100ml i r r e s p e c t i v e o f m o l e c u l a r w e i g h t . The low a d s o r b a n c e and t h e h i g h t h i c k n e s s a t l o w s a l t c o n c e n t r a t i o n a r e due t o t h e e l e c t r o s t a t i c r e p u l s i o n , i . e . , t h e e x c l u d e d volume between the charged groups o f adsorbed p o l y i o n s . As t h e i o n i c s t r e n g t h i s i n c r e a s e d , t h e i n t r a - and i n t e r - p o l y i o n i n t e r a c t i o n s o f a d s o r b e d NaPSS c h a i n s d i m i n i s h s o t h a t a l a r g e r a d s o r b a n c e and s m a l l e r t h i c k n e s s s h o u l d be o b t a i n e d . s

M o l e c u l a r W e i g h t Dependence. The aqueous 4.17 M N a C l s o l u t i o n a t 25 °C was d e t e r m i n e d t o be a t h e t a s o l v e n t f o r NaPSS by T a k a h a s h i , K a t o , and Nagasawa (13) f r o m p r e c i p i t a t i o n measurements. Though T a b l e I shows t h a t t h e d e g r e e o f s u l f o n a t i o n o f t h e NaPSS s a m p l e i s l e s s t h a n u n i t y , a l i n e a r p l o t b e t w e e n the i n t r i n s i c v i s c o s i t i e s o f NaPSS s a m p l e s i n aqueous 4.17 M s o l u t i o n a t 25 °C and t h e s q u a r e r o o t o f t h e m o l e c u l a r weight i s obtained. Thus, we r e g a r d t h e aqueous 4.17 M N a C l s o l u t i o n a t 25 °C as a Theta solvent f o r t h e p r e s e n t NaPSS samples. The m o l e c u l a r w e i g h t s o f t h e NaPSS s a m p l e s g i v e n by the m a n u f a c t u r e r were employed. I n F i g u r e 8, t h e p l a t e a u a d s o r b a n c e , Ap o f NaPSS a t t h e NaPSS c o n c e n t r a t i o n o f 0.04 g/100ml i s p l o t t e d a g a i n s t t h e m o l e c u l a r w e i g h t o f NaPSS on a d o u b l e - l o g a r i t h m i c p l o t f o r s e v e r a l NaCl concentrations. Though d a t a p o i n t s a r e somewhat s c a t t e r e d , the adsorbances are r o u g h l y independent o f the molecular weight. F i g u r e 9 r e p r e s e n t s a d o u b l e - l o g a r i t h m i c p l o t o f the

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

Polyelectrolyte

Adsorption

onto Metal

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TAKAHASHI ETAL.

Figure 4. P l o t s o f t h i c k n e s s , t , a g a i n s t t h e square r o o t of adsorption time. S y m b o l s a r e t h e same a s i n F i g u r e 1.

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

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POLYMER ADSORPTION AND DISPERSION STABILITY

F i g u r e 6. A d s o r b a n c e , Ag, o f N a C l v s . p o l y m e r c o n c e n t r a t i o n f o r NaPSS-3. Symbols a r e t h e same as i n F i g u r e 5.

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

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TAKAHASHI E T A L

Polyelectrolyte

Adsorption

jl/2

onto Metal

1/2

( in ) m

F i g u r e 7. T h i c k n e s s , t , o f t h e a d s o r b e d l a y e r v s . p o l y m e r c o n c e n t r a t i o n f o r NaPSS-3. Symbols a r e t h e same as i n F i g u r e 5.

F i g u r e 8. A d s o r b a n c e , Ap, a t p o l y m e r c o n c e n t r a t i o n o f 0.04 g/100ml v s . t h e m o l e c u l a r w e i g h t . Ο , C ° = 4.17 M; φ , C ° = 0.5 Μ; φ , C ° = 0.1 M. s

s

s

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

POLYMER ADSORPTION AND DISPERSION STABILITY

48

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t h i c k n e s s , t , o f t h e a d s o r b e d l a y e r a t t h e NaPSS c o n c e n t r a t i o n o f 0.04 g/100ml, a g a i n s t t h e m o l e c u l a r w e i g h t . Log t i s l i n e a r w i t h the l o g a r i t h m of the m o l e c u l a r w e i g h t . The s l o p e o f t h e p l o t a t t h e N a C l c o n c e n t r a t i o n o f 4.17 M, w h i c h i s the t h e t a p o i n t f o r t h e NaPSS s a m p l e , i s n e a r l y 0.5 b u t t h e s l o p e s a t t h e l o w e r N a C l c o n c e n t r a t i o n , n a m e l y , good s o l v e n t c o n d i t i o n s a r e l e s s t h a n 0.5. The m o l e c u l a r w e i g h t dependences f o r t h e t h i c k n e s s o f t h e a d s o r b e d NaPSS l a y e r u n d e r T h e t a and good s o l v e n t c o n d i t i o n s a g r e e w i t h t h e c a s e o f a n o n i o n i c p o l y m e r (14). A d s o r b a n c e o f NaPSS, Ap. H e s s e l i n k (J., 2) d e r i v e d a l i n e a r r e l a t i o n s h i p b e t w e e n t h e amount o f p o l y e l e c t r o l y t e a d s o r b e d i n t h e p l a t e a u r e g i o n on an a d s o r b e n t w i t h z e r o s u r f a c e c h a r g e and t h e s q u a r e r o o t o f added s a l t c o n c e n t r a t i o n i n b u l k s o l u t i o n . The t y p i c a l p l a t e a u a d s o r b a n c e f o r t h e NaPSS-3 s a m p l e a t t h e c o n c e n t r a t i o n o f 0.04 g/100ml v a r i e s l i n e a r l y w i t h t h e s q u a r e r o o t o f t h e N a C l c o n c e n t r a t i o n as shown i n F i g u r e 10. E x p a n s i o n o f Thickness of the Adsorbed L a y e r . In the low s a l t c o n c e n t r a t i o n t h e l a r g e t h i c k n e s s compared w i t h t h e c a s e o f t h e T h e t a s o l v e n t (4.17 M N a C l ) i s c o n s i d e r e d t o be due t o t h e e l e c t r o s t a t i c r e p u l s i o n , i . e . , t h e e x c l u d e d v o l u m e e f f e c t o f the a d s o r b e d NaPSS c h a i n s . U s u a l l y , the e x p a n s i o n f a c t o r a > d e f i n e d b y t h e r a t i o o f the t h i c k n e s s i n good s o l v e n t and t h a t i n the Theta s o l v e n t , i s used to q u a n t i t a t i v e l y e v a l u a t e the e x c l u d e d volume e f f e c t f o r t h e a d s o r b e d p o l y m e r s . F o r a d s o r p t i o n o f n o n i o n i c p o l y m e r , Hoeve (15) and J o n e s Richmond (16) a t t e m p t e d t o i n c o r p o r a t e t h e e x c l u d e d - v o l u m e e f f e c t i n t o the expansion f a c t o r , r e s p e c t i v e l y . They s u g g e s t e d t h a t t h e t h i c k n e s s o f t h e a d s o r b e d l a y e r i n good and § s o l v e n t s s h o u l d be t a k e n a t the same adsorbance and molecular weighty respectively. We may c a l c u l a t e t h e e x p a n s i o n f a c t o r a t t h e b u l k NaPSS c o n c e n t r a t i o n o f 0.02 g/100ml, s i n c e t h e a d s o r b a n c e s a r e a l m o s t t h e same f o r t h e r e s p e c t i v e N a C l c o n c e n t r a t i o n s , as s e e n f r o m F i g u r e 5. E x p e r i m e n t a l l y the expansion f a c t o r a of a p o l y e l e c t r o l y t e c h a i n i n b u l k s o l u t i o n i s g i v e n as f o l l o w s (17-19). The α is l a r g e r than a . t

s

t

a

3 s

- 1

«χ,

J

1/C °

(6)

s

where C ° i s the c o n c e n t r a t i o n o f a u n i - u n i v a l e n t s a l t . In F i g u r e 11, t h e ( a 3 - 1) v a l u e f o r NaPSS-3 i s p l o t t e d a g a i n s t the i n v e r s e square r o o t of NaCl c o n c e n t r a t i o n . F i g u r e 11 i l l u s t r a t e s the l i n e a r p r o p o r t i o n a l i t y of a - Î to ^ 1 / C ° . s

t

3

t

S

Conclusions We

s t u d i e d the a d s o r p t i o n o f s o d i u m p o l y ( s t y r e n e s u l f o n a t e )

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

Polyelectrolyte Adsorption

onto Metal

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T A K A H A S H I E T AL.

F i g u r e 10. A d s o r b a n c e , Ap, a t p o l y m e r c o n c e n t r a t i o n o f 0.04 g/100ml f o r NaPSS-3 v s . t h e s q u a r e r o o t o f N a C l concentration.

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

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POLYMER ADSORPTION AND DISPERSION STABILITY

τ

1

1

r

con cen t r a t i on.

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

3.

T A K A H A S H I ET AL.

Polyelectrolyte

Adsorption

onto Metal

51

f r o m aqueous N a C l s o l u t i o n s o n t o a p l a t i n u m s u r f a c e . The a d s o r p t i o n isotherms a r e h i g h a f f i n i t y type and the adsorbance i n the p l a t e a u r e g i o n i s p r o p o r t i o n a l t o t h e square r o o t o f s a l t concentration a t constant molecular weight. The t h i c k n e s s o f t h e a d s o r b e d l a y e r , t , i s a p p r o x i m a t e l y proportional to W a t t h e T h e t a p o i n t b u t i n good s o l v e n t t h e e x p o n e n t o f t h e m o l e c u l a r w e i g h t dependence o f t i s l e s s t h a n 0.5.

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Acknow l e d gmen t s We a c k n o w l e d g e t h e G r a n d - i n - A i d f o r S c i e n t i f i c R e s e a r c h No. 56470079 f r o m t h e M i n i s t r y o f E d u c a t i o n , S c i e n c e , and C u l t u r e o f Japan and t h e A s a h i G l a s s F o u n d a t i o n o f I n d u s t r i a l Technology f o r p a r t i a l s u p p o r t o f t h i s work.

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5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17.

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Noda, I.; Tsuge, T.; Nagasawa, M. J. Phys. Chem. 1970, 74, 710. Nagasawa, M . ; Takahashi, A. in "Light Scattering from Polymer Solutions", Huglin, M. B. E d . ; Academic: New York, 1972; Chap. 16.

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RECEIVED October 7, 1983

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