Segment Density Profiles of Adsorbed Polymers - American Chemical

10 Segment Density Profiles of Adsorbed Polymers

Downloaded by CORNELL UNIV on May 24, 2017 | http://pubs.acs.org Publication Date: February 10, 1984 | doi: 10.1021/bk-1984-0240.ch010

T. COSGROVE, B. VINCENT, and T. L. CROWLEY— University of Bristol, Cantock's Close, Bristol BS81TS,England M. A. COHEN STUART- Laboratory for Physical and Colloid Chemistry, Agricultural University, De Dreijen 6, 6703 BC Wageningen, The Netherlands Segment density profiles and hydrodynamic thickness measurements have been made for a series of polyethylene oxides of molecular weights from 25K to 1.3M adsorbed on polystyrene latex in the 'plateau' region of the adsorption isotherm. At high molecular weights the hydrodynamic thickness occurs at the extremity of the density profile. Comparison with a theoretical model based on solvent flow through a porous layer shows that, although the density profile and the hydrodynamic thickness results are consistent, the experimental profile is not sensitive enough to detect the low concentration of segments in tails at large distances from the interface. This is confirmed by further theoretical calculations based on the Scheutjens and Fleer lattice model for an adsorbed polymer. S e v e r a l e x p e r i m e n t a l parameters have been used t o d e s c r i b e t h e conformation o f a polymer adsorbed a t t h e s o l i d - s o l u t i o n interface; these i n c l u d e t h e t h i c k n e s s o f t h e adsorbed l a y e r (photon c o r r e l a t i o n spectroscopy(J_) ( p . c . s . ) , s m a l l angle neutron s c a t t e r i n g ( 2 ) ( s . a . n . s . ) , e l l i p s o m e t r y ( 3 ) and f o r c e - d i s t a n c e measurements b e t w e e n a d s o r b e d l a y e r s ( 4 ) , and t h e s u r f a c e bound f r a c t i o n ( e . s . r . ( 5 ) , n.m.r. ( 6 ) , c a l o r i m e t r y ( 7 ) and i . r . ( 8 ) ) . However, i t i s v e r y d i f f i c u l t t o d e s c r i b e t h e a d s o r b e d l a y e r w i t h a s i n g l e p a r a m e t e r and i d e a l l y t h e segment d e n s i t y p r o f i l e o f t h e adsorbed c h a i n i s r e q u i r e d . R e c e n t l y s.a.n.s. (9) has been used t o o b t a i n segment d e n s i t y p r o f i l e s f o r p o l y e t h y l e n e o x i d e (PEO) and p a r t i a l l y h y d r o l y s e d p o l y v i n y l a l c o h o l a d s o r b e d o n p o l y s t y r e n e latex. F o r PEO, two t y p e s o f s y s t e m w e r e e x a m i n e d : one where t h e c h a i n s were t e r m i n a l l y - a n c h o r e d a n d t h e o t h e r where t h e p o l y m e r was p h y s i c a l l y a d s o r b e d f r o m s o l u t i o n . The p r o f i l e s f o r t h e s e two 0097-6156/84/0240-0147S06.00/0 © 1984 American Chemical Society

Goddard and Vincent; Polymer Adsorption and Dispersion Stability ACS Symposium Series; American Chemical Society: Washington, DC, 1984.

POLYMER ADSORPTION AND DISPERSION STABILITY


148

c a s e s were m a r k e d l y d i f f e r e n t . The f o r m e r gave a d e n s i t y p r o f i l e w i t h a p r o n o u n c e d maximum and t h e l a t t e r a m o n o t o n i c a l l y decreasing p r o f i l e . These two c a s e s c o r r e s p o n d r e s p e c t i v e l y t o a s y s t e m c o n s i s t i n g o f s h o r t t a i l s and a s y s t e m o f l o o p s , t r a i n s and tails. The PVA s y s t e m gave p r o f i l e s s i m i l a r q u a l i t a t i v e l y t o t h e p h y s i c a l l y a d s o r b e d PEO. I n a l l the c a s e s , however, the e x p e r i m e n t a l p r o f i l e s f e l l somewhat s h o r t o f t h e h y d r o d y n a m i c t h i c k n e s s o b t a i n e d by p . c . s . T h i s s u g g e s t e d t h a t t h e h y d r o d y n a m i c t h i c k n e s s i s d e t e r m i n e d by t h e t a i l s o f t h e d e n s i t y d i s t r i b u t i o n and t h a t s . a . n . s . may n o t be s e n s i t i v e enough t o p i c k up t h e complete d e n s i t y p r o f i l e at the p e r i p h e r y of the adsorbed l a y e r . I n t h i s p a p e r we p r e s e n t r e s u l t s f o r a s e r i e s o f PEO f r a c t i o n s p h y s i c a l l y a d s o r b e d on p e r - d e u t e r o p o l y s t y r e n e l a t e x (PSL) i n t h e ' p l a t e a u r e g i o n o f t h e a d s o r p t i o n i s o t h e r m . H y d r o dynamic and a d s o r p t i o n measurements h a v e a l s o b e e n made on t h i s s y s t e m . U s i n g a p o r o u s l a y e r t h e o r y d e v e l o p e d r e c e n t l y by Cohen S t u a r t (10) we have c a l c u l a t e d t h e h y d r o d y n a m i c t h i c k n e s s o f t h e s e adsorbed polymers d i r e c t l y from the e x p e r i m e n t a l d e n s i t y p r o f i l e s . The r e s u l t s a r e t h e n compared w i t h model c a l c u l a t i o n s b a s e d on d e n s i t y p r o f i l e s o b t a i n e d f r o m t h e S c h e u t j e n s and F l e e r (SF) l a y e r model o f p o l y m e r a d s o r p t i o n ( 1 1 ) . 1

Theoretical The the

Calculations

segment d e n s i t y p r o f i l e o b t a i n e d by s . a . n . s . i s n o r m a l i z e d i n form, #00 p(z)dz =1

(1 )

ο The p h y s i c a l s i g n i f i c a n c e o f t h e e x p e r i m e n t a l p r o f i l e i s t h a t i t i s t h e p r o b a b i l i t y t h a t a segment o f an a d s o r b e d p o l y m e r c h a i n i s a t a d i s t a n c e ζ from the i n t e r f a c e . I n o r d e r to f i n d the volume f r a c t i o n φ(ζ) a t a d i s t a n c e ζ f r o m t h e i n t e r f a c e we r e q u i r e the m a s s / u n i t a r e a Γ and t h e p a r t i a l m o l a r volume o f t h e p o l y m e r v (12) , w h e r e φ(ζ) i s g i v e n by φ(ζ)

= Γνρ(ζ)

(2)

F o r t h e c a l c u l a t i o n o f t h e h y d r o d y n a m i c t h i c k n e s s we d i v i d e the p r o f i l e a r t i f i c i a l l y i n t o e l e m e n t a r y l a y e r s , t h e r e s u l t b e i n g independent o f the d i v i s i o n chosen p r o v i d e d i t i s s u f f i c i e n t l y fine. The s . a . n . s . d a t a i s o b t a i n e d as a f u n c t i o n o f Q, t h e wave v e c t o r (4π/λ s i n ( 6 / 2 ) , where λ i s t h e n e u t r o n w a v e l e n g t h and θ t h e s c a t t e r i n g a n g l e . The Q r e s o l u t i o n c o r r e s p o n d s i n r e a l s p a c e t o a f r a c t i o n o f a bond l e n g t h w h i c h i s s m a l l enough f o r d e f i n i n g an elementary l a y e r .


10.

COSGROVE ET AL.

Adsorbed Polymer Segment Density Profiles

149

F o l l o w i n g Cohen S t u a r t (10) we c h o o s e a s e m i - e m p i r i c a l c o n t i n u o u s f u n c t i o n t o r e l a t e t h e h y d r o d y n a m i c p e r m e a b i l i t y , k, t o the volume f r a c t i o n k = α(ΐ - φ)/φ

(3)

where a i s a n e x p e r i m e n t a l l y d e t e r m i n e d c o n s t a n t f r o m s e d i m e n t a t i o n experiments, k i s related to the sedimentation c o e f f i c i e n t s o f t h e p o l y m e r b y (10)


c(i

- v77v ) 1 ο

(4)

where η i s t h e s o l v e n t v i s c o s i t y , c t h e p o l y m e r c o n c e n t r a t i o n a n d V£ a n d V t h e p a r t i a l s p e c i f i c v o l u m e s o f p o l y m e r a n d s o l v e n t respectively. Hence u s i n g t h e e q u a t i o n s d e v e l o p e d i n (10) we c a n c a l c u l a t e the hydrodynamic t h i c k n e s s d i r e c t l y from the experimental density p r o f i l e . Q

Experimental The s . a . n . s . e x p e r i m e n t s w e r e c a r r i e d o u t u s i n g t h e D17 camera a t t h e I . L . L . , G r e n o b l e . D a t a w e r e c o l l e c t e d a t two w a v e l e n g t h s , 0.8 and 1.4 nm a t a sample t o d e t e c t o r d i s t a n c e o f 1.8 m. The o v e r l a p p i n g s p e c t r a w e r e combined t o g i v e a s u f f i c i e n t l y w i d e Q r a n g e to enable t h e data t o be n u m e r i c a l l y i n v e r t e d t o o b t a i n t h e d e n s i t y d i s t r i b u t i o n s . The l a t e x d i s p e r s i o n s w e r e p r e p a r e d a t a s o l i d s c o n c e n t r a t i o n o f 4% a n d p o l y m e r s o l u t i o n c o n c e n t r a t i o n s between 200 a n d 300 ppm. The s e d i m e n t a t i o n e x p e r i m e n t s w e r e c a r r i e d o u t u s i n g a n u l t r a centrifuge . The p . c . s . measurements were c a r r i e d o u t u s i n g a M a l v e r n m u l t i b i t c o r r e l a t o r and s p e c t r o m e t e r t o g e t h e r w i t h a mode s t a b i l i z e d Coherent Krypton-ion l a s e r . The r e s u l t i n g t i m e c o r r e l a t i o n f u n c t i o n s were a n a l y s e d u s i n g a n o n - l i n e a r l e a s t s q u a r e s p r o c e d u r e o n a PDP11 c o m p u t e r . The l a t e x d i s p e r s i o n s were f i r s t d i l u t e d t o a p p r o x i m a t e l y 0.02% s o l i d s a f t e r w h i c h p o l y m e r s o l u t i o n o f t h e r e q u i r e d c o n c e n t r a t i o n was added. The s a m p l e s o f t h e 9 6 % d e u t e r a t e d l a t e x w e r e p r e p a r e d b y a standard s u r f a c t a n t - f r e e procedure which i s described f u l l y e l s e where ( 1 3 ) . The n a r r o w d i s t r i b u t i o n f r a c t i o n s o f PEO w e r e o b t a i n e d f r o m P o l y m e r L a b s (Shawbury) a n d were m a n u f a c t u r e d b y t h e T o y a Soda Co. The d e t a i l s o f t h e s e s a m p l e s a r e g i v e n i n T a b l e I . Results T a b l e I g i v e s d e t a i l s o f t h e a d s o r b e d amounts f o r t h e s i x p o l y m e r f r a c t i o n s o b t a i n e d a t a n e q u i l i b r i u m c o n c e n t r a t i o n o f 2000 ppm. Based o n t h e f u l l a d s o r p t i o n i s o t h e r m (2) t h e s e v a l u e s correspond



150


Table I .

3

MwÎ(xl0" ) 25 40 73 150 280 660 1290 τ t * £

E x p e r i m e n t a l d a t a f o r PEO a d s o r b e d PSL ( d i a m e t e r 240 ±4nm)

2Rg*V nm 12.7 17.5 23.7 40.4 56.9 91 .4 156.4

6 /nm p . c . s . u

5.8 12.0 17.3 28.9 53.0 95.2 160.0

± 1.5 ± 3.0 ± 5.0 ± 3.0 ± 3.0 ±10.0 ±10.0

ό /run s . a . n . s . Η 2.3 2.8 5.7 7.8 12.3 15.1

-

on

Trng/m^ 0.56 0.68 0.89 0.99 1.21 1 .42 1 .74

± ± ± ± ± ± ±

0.5 0.5 0.5 0.5 0.5 0.5 0.5t

maximum p o l y d i s p e r s i t y 1.14 estimated m e a s u r e d a t a s o l u t i o n c o n c e n t r a t i o n o f 2000 ppm a t 25 C i n t e r p o l a t e d u s i n g t h e r e s u l t s o f Cabane e t a l . J . P h y s i q u e ( 1 9 8 2 ) , 4 3 , 1579.


10.

COSGROVE E T A L


151

1

to a d s o r p t i o n i n t h e ' p l a t e a u r e g i o n . The h y d r o d y n a m i c t h i c k n e s s e s and 2Rg (Rg r a d i u s o f g y r a t i o n o f t h e f r e e c o i l s i n s o l u t i o n ) are a l s o g i v e n . A l s o l i s t e d are the hydrodynamic t h i c k n e s s e s c a l c u l a t e d from the s.a.n.s. d e n s i t y p r o f i l e s ( 6 ). F i g u r e 1 shows t h e u l t r a c e n t r i f u g a t i o n d a t a p l o t t e d u s i n g E q u a t i o n 3. The p l o t i s r e a s o n a b l y l i n e a r g i v i n g a v a l u e f o r α o f 0.5 ±0.03 nm^. F i g u r e 2 shows t h e e x p e r i m e n t a l d e n s i t y p r o f i l e s f o r t h r e e o f t h e s a m p l e s s t u d i e d (Mw 73K, 150K a n d 660K) and t h e c o r r e s p o n d i n g c a l c u l a t e d v a l u e s o f t h e h y d r o d y n a m i c t h i c k n e s s e s . The p . c . s . h y d r o d y n a m i c t h i c k n e s s ( 6 ) i salso shown f o r t h e 150K s a m p l e . s a n s

H

p c s

H


Discussion In p r i n c i p l e , u s i n g t h e porous l a y e r theory, i t i s p o s s i b l e t o o b t a i n the hydrodynamic t h i c k n e s s o f an adsorbed l a y e r u s i n g t h e e x p e r i m e n t a l d e n s i t y p r o f i l e a n d t h e p e r m e a b i l i t y f u n c t i o n . The r e s u l t s o f t h i s c a l c u l a t i o n are given i n Table I . I n f i g u r e 2 i t c a n be s e e n t h a t t h e c a l c u l a t e d 6 values f a l l w i t h i n the t a i l of the s.a.n.s. d e n s i t y p r o f i l e s . However, c o m p a r i s o n w i t h t h e r e s u l t s o b t a i n e d b y p . c . s . ( T a b l e I ) show a l a r g e s y s t e m a t i c discrepancy. Values o f ô ^ i n a s i m i l a r s y s t e m have b e e n p u b l i s h e d b y K a t o (14) a n d t h e r e i s v e r y good agreement w i t h t h e p r e s e n t v a l u e s a l t h o u g h t h e i r q u o t e d a d s o r b e d amounts a r e r a t h e r l a r g e . Klein and Luckham (4) h a v e u s e d a t e c h n i q u e b a s e d o n t h e d i r e c t m e a s u r e ment o f t h e f o r c e s e p a r a t i o n f u n c t i o n b e t w e e n two m i c a s u r f a c e s c o v e r e d w i t h a d s o r b e d PEO c h a i n s i n w a t e r . From t h e s e r e s u l t s they i n f e r a ' s t e r i c ' t h i c k n e s s based on an i n i t i a l i n t e r a c t i o n . I n t e r e s t i n g l y t h e i r measurements c o r r e s p o n d a l m o s t t o 2Rg. of the free c o i l s i n s o l u t i o n . Their r e s u l t s together with the p . c . s . r e s u l t s a n d 2Rg a r e shown i n F i g u r e 3. C l e a r l y b o t h t h i c k n e s s e s t i m a t e s a r e s e n s i t i v e t o p o l y m e r segments a t t h e p e r i p h e r y o f the adsorbed l a y e r . The e x p e r i m e n t a l t h i c k n e s s measurements may a l s o b e compared w i t h t h e o r e t i c a l r e s u l t s b a s e d on p r o f i l e s g e n e r a t e d b y t h e S.F., S c h e u t j e n s F l e e r , t h e o r y ( 1 1 ) . F o r t h i s c a l c u l a t i o n we u s e a v a l u e for x o f 1 ( n e t a d s o r p t i o n f r e e e n e r g y ) , f o r χ o f 0.45 ( e x p e r i m e n t a l v a l u e o f t h e F l o r y - H u g g i n s p a r a m e t e r ) and a p o l y m e r s o l u t i o n c o n c e n t r a t i o n o f 200 ppm. A l t h o u g h t h e v a l u e f o r x seems r a t h e r a r b i t r a r y i t h a s b e e n shown (10) t h a t 6^ i s i n s e n s i t i v e t o t h i s parameter. F i g u r e 4 shows t h e h y d r o d y n a m i c t h i c k n e s s c a l c u l a t e d f o r c h a i n s o f v a r i o u s l e n g t h s , t o g e t h e r w i t h 2Rg c a l c u l a t e d a c c o r d i n g to t h e r e l a t i o n R g = ( r / o ^ ^ w h e r e r i s t h e number o f monomers. The t r e n d s observed i n b o t h t h e e x p e r i m e n t a l ( F i g u r e 3 ) and t h e p u r e l y t h e o r e t i c a l ( F i g u r e 4) c a s e s a r e v e r y s i m i l a r : a t low molecular w e i g h t s 6JJ i s l e s s t h a n 2Rg b u t c r o s s e s t h e 2Rg l i n e a t h i g h molecular weight. The d i f f e r e n t e x p o n e n t s f o r 2Rg and ojj a r e due t o t h e i n c r e a s i n g i m p o r t a n c e o f t a i l s w i t h i n c r e a s i n g s a n s

H

C

S

g

s




Η -

73

m

ζ

Ο

•ν

N>

Goddard and Vincent; Polymer Adsorption and Dispersion Stability ACS Symposium Series; American Chemical Society: Washington, DC, 1984. 20.0

Dietanoe from e u r f α ο · (nm)

10.0

S

H

30.0

S 3 n S

40.

H

P

Figure 2. Experimental segment density p r o f i l e s f o r P E O adsorbed on P S latex i n water. Molecular weights 73K, 150K, and 660K. V e r t i c a l l i n e s correspond to estimates of the hydrodynamic thickness ( d ) from the experimental p r o f i l e s . Also shown i s the ô ° value f o r the 150K sample

0.0




"V

Η •
ο 2

δ

73

Ο

χ.

> α

m 73

Ο Q


F i g u r e 4. H y d r o d y n a m i c t h i c k n e s s (•) and 2Rg (+) as a f u n c t i o n o f c h a i n l e n g t h c a l c u l a t e d on t h e b a s i s o f t h e o r e t i c a l d e n s i t y p r o f i l e s u s i n g t h e SF t h e o r y .


POLYMER ADSORPTION AND DISPERSION STABU ITY

156

m o l e c u l a r w e i g h t . The a g r e e m e n t b e t w e e n t h e e x p o n e n t f o r t h e p . c . s . measurements (0.8 ±0.003) a n d f o r t h e p u r e l y t h e o r e t i c a l c a l c u l a t i o n (0.8 ±0.05) i s v e r y c l o s e . I t would appear t h a t the p.c.s. r e s u l t s are c o n s i s t e n t w i t h b o t h p u b l i s h e d e x p e r i m e n t a l d a t a and w i t h t h i s t h e o r e t i c a l model. T h i s must c a s t some d o u b t o n the h y d r o d y n a m i c t h i c k n e s s c a l c u l a t e d from the s.a.n.s. p r o f i l e . From T a b l e I we c a n s e e that the values o f δ a r e c o n s i d e r a b l y l a r g e r than and t h a t t h i s d i s c r e p a n c y becomes more p r o n o u n c e d a t h i g h e r m o l e c u l a r weights. T h i s i s i l l u s t r a t e d i n F i g u r e 2 where t h e p . c . s . r e s u l t f o r t h e 150K s a m p l e i s f o u n d i n a r e g i o n where t h e r e i s no d e t e c t a b l e i n t e n s i t y from the neutron s c a t t e r i n g experiment. This suggests t h a t t h e s.a.n.s. experiment i s n o t s u f f i c i e n t l y s e n s i t i v e t o d e t e c t t h e v e r y l o w segment d e n s i t y ( o f t a i l s ) w h i c h determine the p.c.s. hydrodynamic t h i c k n e s s (10). To e x p l o r e t h i s i n more d e t a i l i t i s u s e f u l t o compare t h e e x p e r i m e n t a l p r o f i l e s w i t h t h o s e c a l c u l a t e d f r o m t h e S.F. t h e o r y . F i g u r e 5 shows a p r o f i l e f o r 2000 s e g m e n t s , u s i n g t h e same p a r a m e t e r s a s a b o v e . T h i s p r o f i l e c a n b e q u a l i t a t i v e l y compared w i t h t h e e x p e r i m e n t a l p r o f i l e s i n F i g u r e 2. The m a j o r d i f f e r e n c e b e t w e e n t h e t h e o r e t i c a l a n d e x p e r i m e n t a l p r o f i l e s i s the p r e s e n c e o f a s m a l l b u t s i g n i f i c a n t segment d e n s i t y a t l a r g e d i s t a n c e s f r o m the i n t e r f a c e , which i s n o t found e x p e r i m e n t a l l y . This d i f f e r e n c e i n shape i s c l e a r l y s e e n when t h e p r o f i l e s a r e s u p e r i m p o s e d . Also i n F i g u r e 5 we show t h e h v d r o d y n a m i c t h i c k n e s s c a l c u l a t e d u s i n g the whole p r o f i l e ( 6 ^ ) and f o r a d i s t r i b u t i o n from w h i c h t a i l s were excluded (δ ) g i v i n g v a l u e s o f 32.0 a n d 12.0 l a y e r s r e s p e c t i v e l y . The r a t i o o f t h e s e numbers i s s i m i l a r t o t h e r a t i o found between δ and ô from experiment and s u g g e s t s t h a t t h e s . a . n . s . e x p e r i m e n t d e t e c t s most o f t h e d i s t r i b u t i o n a s s o c i a t e d w i t h t r a i n s and loops b u t o n l y a s m a l l p a r t o f t h e t a i l distribution. Although i t i s d i f f i c u l t t o estimate the threshold of s e n s i t i v i t y o f the s.a.n.s. experiment i t i s e s t i m a t e d t o be o f the o r d e r o f 1% o f t h e segment d e n s i t y . A simple procedure t o demonstrate t h i s e f f e c t o f s e n s i t i v i t y is to truncate thetheoretical p r o f i l e s a t d i f f e r e n t layers. I n F i g u r e 5 v a l u e s o f t h e h y d r o d y n a m i c t h i c k n e s s a r e shown when t h e p r o f i l e i s t r u n c a t e d a t 1% a n d a t 2%. T h i s c l e a r l y shows t h e e f f e c t t h a t r e d u c i n g the s e n s i t i v i t y d r a m a t i c a l l y reduces t h e h y d r o d y n a m i c t h i c k n e s s a s i t e l i m i n a t e s segments a t t h e e x t r e m i t y of the adsorbed l a y e r . I n a p r e v i o u s p a p e r (15) t h e segment d e n s i t y o f PVA a d s o r b e d on PS l a t e x i n w a t e r was p r e s e n t e d a n d i t was n o t e d t h a t δ was a t t h e e x t r e m i t y o f t h e s . a . n . s . p r o f i l e . C a l c u l a t i n g δ^ a s s u m i n g a v a l u e o f α o f 0.5 nm^ g i v e s 13 nm i n c o n t r a s t t o t h e e x p e r i m e n t a l v a l u e o f 18 nm. The d i s c r e p a n c y h e r e i s much s m a l l e r t h a n i n t h e c a s e o f PEO. T h i s e f f e c t i s d i f f i c u l t t o i n t e r p r e t w i t h o u t f u r t h e r t h e o r e t i c a l w o r k b u t may b e a t t r i b u t a b l e t o t h e f a c t t h a t t h e PVA c h a i n i s l e s s f l e x i b l e t h a n PEO a n d t h a t t h e b l o c k s t r u c t u r e (PVA i s a random b l o c k c o p o l y m e r o f v i n y l a c e t a t e , 12%, a n d v i n y l a l c o h o l ) makes t h e f o r m a t i o n o f t a i l s l e s s l i k e l y . ρ


Η

t o t a

H

o p s

Η

ρ ο δ

Η

s a n s

H

ρ

Η


s

a

n

s


a d

d

1.0

13.5

Lay m

truncated Λ 14 1312 loops only

Number

26.0

a. 38. 5

1 full profile

51.

F i g u r e 5. SF t h e o r e t i c a l d e n s i t y p r o f i l e f o r 2000 segments. X = 1, X = 0.45 a n d a p o l y m e r s o l u t i o n c o n c e n t r a t i o n o f 200 ppm. V e r t i c a l l i n e s c o r r e s p o n d t o 0^ v a l u e s c a l c u l a t e d u s i n g ( 1 ) t h e f u l l p r o f i l e , ( 2 ) t h e p r o f i l e f o r l o o p s o n l y , ( 3 ) t h e f u l l p r o f i l e t r u n c a t e d a t 1%, a n d ( 4 ) a t 2% volume f r a c t i o n .

: ι

m

in CM



158

Conclusion Segment d e n s i t y p r o f i l e s a n d h y d r o d y n a m i c t h i c k n e s s measurements have b e e n made f o r p o l y e t h y l e n e o x i d e s a d s o r b e d on p o l y s t y r e n e latex. C o m p a r i s o n w i t h t h e o r e t i c a l m o d e l s shows t h a t t h e h y d r o dynamic t h i c k n e s s i s d e t e r m i n e d b y p o l y m e r segments ( t a i l s ) a t t h e extremity of the d i s t r i b u t i o n . I t i s a l s o concluded that the s e n s i t i v i t y o f t h e s . a . n . s . e x p e r i m e n t p r e c l u d e s t h e measurement o f segments i n t h i s r e g i o n and t h a t t h e e x p e r i m e n t a l segment d e n s i t y p r o f i l e s a r e e s s e n t i a l l y d o m i n a t e d b y l o o p s and t r a i n s .


Acknowledgments The a u t h o r s w o u l d l i k e t o a c k n o w l e d g e NATO f o r p r o v i d i n g f u n d s t o e n c o u r a g e c o l l a b o r a t i o n b e t w e e n t h e r e s e a r c h g r o u p s i n Wageningen and B r i s t o l . The I . L . L . i s a c k n o w l e d g e d f o r p r o v i d i n g f a c i l i t i e s f o r c a r r y i n g o u t t h e s . a . n . s . e x p e r i m e n t s and p r o v i d i n g g e n e r a l facilities. D r . Derek Cebula i s thanked f o r h i s a s s i s t a n c e d u r i n g the e x p e r i m e n t a l r u n s . J . B i s h o p and P. C o l l i e r a r e t h a n k e d f o r obtaining the p.c.s. r e s u l t s . The SERC i s a c k n o w l e d g e d f o r g r a n t s f o r equipment (p.c.s.) and f o r p o s t - d o c t o r a l f e l l o w s h i p s f o r T.L. C r o w l e y and J . B i s h o p . D r . Th.F. T a d r o s ( I C I ) i s t h a n k e d f o r h i s c o n t i n u i n g i n t e r e s t i n t h i s p r o j e c t . D r . G.F. F l e e r i s thanked f o r s t i m u l a t i n g a n d e n l i g h t e n i n g d i s c u s s i o n s on a s p e c t s o f t h e theory o f polymer a d s o r p t i o n .

Literature Cited 1. Garvey, M.J.; Tadros, Th.F.; Vincent, B. J. Coll. and Interface Sci. 1976, 55, 440. 2. Cosgrove, T.; Vincent, B.; Crowley, T. L.; Barnett, K. G.; King, Τ. Α.; Tadros, Th. F.; Burgess, A. N. Polymer 1981, 75, 4115. 3. Grant, W. H.; Morrisey, B. W.; Stromberg, R. R. Poly. Sci. Tech. 1975, (A)9, 43. 4. Luckham, P.F.; Klein, J . ; Nature, 1983, 300, 429. 5. Robb. I.D.; Smith, R. Eur. Poly. J. 1974, 10, 1005. 6. Cosgrove, T.; Vincent, B.; Barnett, K.G.; Cohen Stuart,Μ.Α.; Macromolecules 1981, 14, 1018. 7. Killmann, E.; Korn, M. J. Coll. and Interface Sci. 1980, 76, 19. 8. Cohen Stuart, M.A.; Fleer, G.J.; Bijsterbosch, B.H. J. Coll. Interface Sci. 1982, 90, 321 9. Cosgrove, T.; Vincent, B.; Crowley, T.L. Faraday Symposia 1981, 16, 101. 10. Cohen Stuart,M.A;Cosgrove, T.; Vincent, B. Macromolecules (submitted).


10.

COSGROVE ET AL.


159

11. Scheutjens, J.M.H.M.; Fleer, G.J. J. Phys. Chem. 1979, 83, 1619; 1980, 84, 178. 12. Brandrupt, J . ; Immergut, E.H. "Polymer Handbook"; J. Wiley 1975. 13. Barnett, K.G. Ph.D. Thesis, Bristol University, 1982. 14. Kato, T.; Nakamura, K.; Kawasuchi, M.; Takahashi, A. Poly J. 1981, 13, 1037. 15. Cosgrove, T.; Vincent, B.; Crowley, T. in "Adsorption from Solution"; Ottewill, R.H.; Rochester, C.H.; Smith, A.L., Eds.; Academic: New York, 1983, 287. October 7, 1983


RECEIVED


Segment Density Profiles of Adsorbed Polymers - American Chemical

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