Solid Interface

5 Solvent Effects on Adsorption at the Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on September 21, 2015 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0087.ch005

Polymer/Solid Interface M . J . SCHICK and Ε. N . H A R V E Y , JR. Central Research Laboratories, Interchemical Corporation, Clifton, N . J.

The adsorption on Graphon

of polystyrene- C 14

(PS- C,

M

14

w

=

292,000)

carbon black was studied from six solvents

covering a range of solvent power. The results indicate in creased adsorption

of PS- C 14

on Graphon

with decreasing

solvent power. Similarly, correlation between the of PS- C 14

PS- C 14

on Graphon and the hydrodynamic

in solution is good; i.e., A

8

adsorption

dimensions of

increases with decreasing

end-to-end root-mean-square length of the polymer in solu tion

() . 2

1/2

It is postulated that under conditions of

weak segment-surface

interaction

a uniformly

adsorbing

polymer like polystyrene attaches itself to the Graphon sur face from good solvents as a flat oriented monolayer; from a poor solvent the polymer assumes a loop or coil structure in which only part of the polymer segments are attached directly to the Graphon

surface.

/ C o m p r e h e n s i v e r e v i e w s d e a l i n g w i t h t h e a d s o r p t i o n of p o l y m e r s ^

at

s o l i d - l i q u i d interfaces h a v e r e c e n t l y b e e n p u b l i s h e d b y H u g h e s a n d

F r a n k e n b e r g (13),

P a t a t , K i l l m a n , a n d S c h l i e b e n e r (18, 19),

B u l a s , R o t h s t e i n , a n d E i r i c h (21),

K i p l i n g (14),

Rowland,

and Stromberg

(9,27).

T h e factor of p r i m a r y interest i n the p r o b l e m at h a n d , the effect of solvent o n p o l y m e r a d s o r p t i o n i n n o n a q u e o u s

systems, has b e e n

subject of s e v e r a l investigations (2, 6, 8, 11, 12, 15, 16, 20, 22, 25,

the 28).

I n g e n e r a l , a m a r k e d d e p e n d e n c e of p o l y m e r a d s o r p t i o n o n solvent u s e d was observed.

S e v e r a l of these d a t a s u p p o r t the c o n t e n t i o n that p o l y m e r s

are s t r o n g l y a d s o r b e d f r o m p o o r solvents a n d t h a t the reverse h o l d s t r u e for g o o d solvents ( I I , 12, 15, 16, 22, 25, 28).

H o w e v e r , this strict d e

p e n d e n c e of a d s o r p t i o n o n solvent p o w e r is o v e r s h a d o w e d i n m a n y cases b y the i n t e r a c t i o n b e t w e e n p o l y m e r a n d adsorbent ( 8 ) , strong c o m p e t i t i o n b e t w e e n solvent a n d p o l y m e r for the surface of the adsorbent 63 In Interaction of Liquids at Solid Substrates; Alexander, A.; Advances in Chemistry; American Chemical Society: Washington, DC, 1968.

(2,17,

64

INTERACTION

O F LIQUIDS A T SOLID

SUBSTRATES

20), o r m o l e c u l a r w e i g h t effects ( 1 6 ) . T h e r e f o r e , i t a p p e a r e d d e s i r a b l e to e s t a b l i s h a r i g o r o u s c o r r e l a t i o n b e t w e e n s o l u t i o n a n d surface p r o p e r t i e s as a f u n c t i o n of solvent p o w e r

i n a w e l l - c h a r a c t e r i z e d system u n d e r

c o n d i t i o n s i n w h i c h t h e adsorbent surface w a s at a l l t i m e i n contact w i t h t h e e q u i l i b r i u m s o l u t i o n of t h e adsorbate. T h e system d e s c r i b e d i n this i n v e s t i g a t i o n is p o l y s t y r e n e - C a d Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on September 21, 2015 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0087.ch005

14

sorbed

on Graphon carbon black

( g r a p h i t i z e d S p h e r o n 6 ) f r o m six

solvents c o m p r i s i n g a w i d e s p e c t r u m f r o m g o o d to p o o r solvent p o w e r . W e l l - c h a r a c t e r i z e d m a t e r i a l s w e r e selected to e l u c i d a t e t h e c o n f o r m a t i o n of p o l y m e r m o l e c u l e s at t h e s o l i d / l i q u i d interface.

So far t w o models

h a v e b e e n p o s t u l a t e d t o d e s c r i b e t h e c o n f o r m a t i o n of t h e a d s o r b e d p o l y m e r m o l e c u l e s at t h e s o l i d / l i q u i d interface ( 9 , 1 3 , 14, 18,19, 21, 27). I n the first m o d e l t h e p o l y m e r assumes a l o o p o r c o i l s t r u c t u r e i n w h i c h o n l y a f r a c t i o n of t h e p o l y m e r segments a r e a t t a c h e d d i r e c t l y at t h e interface, a n d i n t h e s e c o n d m o d e l t h e p o l y m e r forms a r e l a t i v e l y flat a n d c o m pressed

interfacial layer w i t h

many

segments

a t t a c h e d to t h e s o l i d

substrate. Experimental Graphon black, kindly furnished b y the Cabot Corporation, was the a d s o r b e n t ; a n d i t s p h y s i c a l properties a r e l i s t e d i n T a b l e I . T h e t e r m " G r a p h o n " refers t o S p h e r o n 6 w h i c h h a d b e e n h e a t e d t o 2 , 7 0 0 ° - 3 , 2 0 0 ° C . T h i s g r a p h i t i z e d n o n p o r o u s c a r b o n b l a c k is a u n i q u e f o r m of c a r b o n w i t h u n i f o r m surface a n d h i g h surface area. T h e G r a p h o n samples w e r e d r i e d f o r 12 hrs. at 1 4 0 ° C . a n d stored in vacuo b e f o r e u s e i n t h e a d s o r p t i o n experiments. L a b e l l e d p o l y s t y r e n e - C ( P S - C ) w a s t h e adsorbate. T w o batches were prepared b y a n identical procedure w i t h only one of them contain ing radioactive C . T h e labelled polymer was used for the adsorption measurements, whereas t h e u n l a b e l l e d p o l y m e r w a s u s e d f o r t h e d e t e r m i n a t i o n o f t h e s o l u t i o n properties. T h e p o l y s t y r e n e w a s 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 of r e d i s t i l l e d styrene. I n o r d e r to r e m o v e u n reacted monomer the polystyrene was freeze-dried from benzene solution. 14

1 4

1 4

Table I.

Properties of Graphon Carbon Black

Manufacturer

Cabot

Code number

S6-D4

Nitrogen surface area (sq. meter/gram)

89.70

Electron microscope surface area (sq. meter/gram)

117.00

Electron microscope particle diameter d

n

(ηΐμ)

23.50

Electron microscope particle diameter d

A

(m^)

27.60

Nitrogen particle diameter d

A

(m/x)

36.00

In Interaction of Liquids at Solid Substrates; Alexander, A.; Advances in Chemistry; American Chemical Society: Washington, DC, 1968.

SCHICK

5.

A N D HARVEY,

Polymer/Solid Interface

JR.

65

T h e viscosity-average molecular weight of the polystyrene sample, Μ = 251,000, w a s c a l c u l a t e d f r o m i n t r i n s i c v i s c o s i t y measurements i n toluene a n d b u t a n o n e - 2 solutions (see T a b l e I I ) b y t h e M a r k - H o u w i n k e q u a t i o n [η] = K ' M . T h e constants w e r e K' = 1.7 X 1 0 a n d a — 0.69 for t h e toluene solutions at 2 5 . 0 ° C . a n d K ' — 3.9 Χ 1 0 " a n d a — 0.58 for t h e b u t a n o n e - 2 solutions at 25.0 ° C . ( 2 9 , 30). F o r c o m p a r i s o n t h e w e i g h t - a v e r a g e m o l e c u l a r w e i g h t M = 292,000 w a s d e t e r m i n e d f r o m l i g h t scattering measurements i n toluene solutions. T h e specific a c t i v i t y of t h e l a b e l l e d p o l y s t y r e n e s a m p l e w a s 0.0055 m c . / g r a m . γ

a

- 4

4

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on September 21, 2015 | http://pubs.acs.org Publication Date: June 1, 1968 | doi: 10.1021/ba-1968-0087.ch005

w

T h e solvents w e r e o f a n a l y t i c a l g r a d e a n d w e r e u s e d w i t h o u t f u r t h e r p u r i f i c a t i o n w i t h t h e e x c e p t i o n of b e n z e n e , w h i c h w a s r e d i s t i l l e d a n d stored o v e r s o d i u m pellets. T h e a d s o r p t i o n experiments w e r e r u n i n 5 0 - m l . glass-stoppered E r l e n m e y e r flasks filled w i t h 2 5 m l . adsorbate s o l u t i o n a n d 0.125 g r a m adsorbent. T h e flasks w e r e a g i t a t e d b y a m e c h a n i c a l shaker e n c l o s e d i n a n a i r thermostat a t 25.0 ° C . A f t e r 40-hr. a g i t a t i o n p e r i o d s , t h e s u s p e n sions w e r e c e n t r i f u g e d ; t h e n t h e c o n c e n t r a t i o n o f t h e u n a d s o r b e d p o l y m e r w a s d e t e r m i n e d b y r a d i o a c t i v e assay ( C ) o f a l i q u o t s o f t h e s u p e r n a t a n t l i q u i d o n p l a n c h e t s i n a G e i g e r - M u l l e r C o u n t e r w i t h a d e c a d e scaler a n d a p r i n t i n g t i m e r . A l l counts w e r e r u n i n d u p l i c a t e o r t r i p l i c a t e . T h e r e p r o d u c i b i l i t y o f t h e a d s o r p t i o n experiments w a s w i t h i n ±2.5%. Rate studies h a v e c o n f i r m e d that there is n o m e a s u r a b l e increase i n a m o u n t of p o l y s t y r e n e a d s o r b e d o n G r a p h o n f r o m b e n z e n e solutions after 36 h r s . 1 4

Table II. Effect of Solvent on the Adsorption of Polystyrene- C on Graphon at 2 5 . 0 ° C . 14

a

A*

Surface Properties A, mg./gram

0.74 0.69

509 500 491 414 409 326

55 40 129 160 160 175

Solution Properties w . dl/gram

α

Solvent Benzene Toluene Dioxane Butanone-2 E t h y l acetate Cyclohexane (^-solvent)

8

h

0.430 0.434 0.472 0.485 0.485 0.499

0.95 0.90 0.85 0.51 0.49 0.25

c

— 0.58

— 0.50

e

Thermodynamic compatibility constant. It has recently also been denoted to the symbol χι. Intrinsic viscosity: = 0.025 signifies a rigid sphere. "Exponent in Mark-Houwink equation [rç] = K'M : a = 0.5 signifies a rigid sphere or compact coil and a = 1.4 a rodlike or highly extended molecule. ( < r > ) : end-to-end, root-mean-square length derived from the Flory-Fox equa( ) tion [>] = Φ where Φ = 2.1 Χ 1 0 is the universal constant. Data calAï culated on the basis of M = 292,000. A , : extrapolated saturation concentration from adsorption isotherm plots of A in mg. polystyrene- C adsorbed per gram of Graphon vs. concentration of supernatant liquid in mg./ml.

α

b

&

d

2

1 / 2

2

3 / 2

21

w

e

14


66

INTERACTION

O F LIQUIDS A T SOLID

SUBSTRATES

Results and Discussion It is a w e l l k n o w n fact that t h e c o n f i g u r a t i o n of p o l y m e r m o l e c u l e s i n s o l u t i o n changes m a r k e d l y w i t h solvent p o w e r (1, 29, 30). T h i s p h e n o m e n o n has b e e n u t i l i z e d i n this s t u d y t o a d v a n c e o u r e x p e r i m e n t a l


k n o w l e d g e o f t h e c o n f o r m a t i o n of p o l y m e r m o l e c u l e s at t h e s o l i d / l i q u i d interface f r o m a c o r r e l a t i o n o f s o l u t i o n w i t h a d s o r p t i o n p r o p e r t i e s of a specific p o l y m e r - s o l v e n t system. S u c h a c o r r e l a t i o n is g i v e n i n T a b l e I I for t h e m o l e c u l a r d i m e n s i o n s o f a p o l y s t y r e n e s a m p l e i n six solvents, c o m p r i s i n g a w i d e s p e c t r u m f r o m g o o d t o p o o r solvent p o w e r , w i t h t h e c o r r e s p o n d i n g a d s o r p t i o n d a t a at t h e G r a p h o n / s o l u t i o n interface. T h e F l o r y - H u g g i n s t h e o r y is g e n e r a l l y a p p l i e d to define t h e t h e r m o d y n a m i c properties of a p o l y m e r s o l u t i o n (1).

I t gives a n expression

for e x p e r i m e n t a l l y o b t a i n a b l e q u a n t i t i e s s u c h as t h e p a r t i a l m o l a r free energy o f m i x i n g .

w h e r e χ is t h e degree o f p o l y m e r i z a t i o n . AF

1

m a y be experimentally

d e t e r m i n e d f r o m c o l l i g a t i v e p r o p e r t y measurements.

Thus, the compati

b i l i t y constant μ is a u s e f u l e m p i r i c a l p a r a m e t e r f r o m w h i c h t h e solvent p o w e r of a p o l y m e r s o l u t i o n m a y b e d e t e r m i n e d . Its v a l u e increases w i t h d e c r e a s i n g solvent p o w e r u p t o 0.55, w h e n phase s e p a r a t i o n occurs. T h e μ values l i s t e d i n t h e first c o l u m n o f T a b l e I I are t a k e n f r o m a n osmotic pressure s t u d y o f S c h i c k (23,24) o n p o l y s t y r e n e ( M = 540,000 o r M — n

v

890,000), w i t h t h e e x c e p t i o n of t h e v a l u e f o r b e n z e n e , w h i c h is t a k e n f r o m B r e i t e n b a c h a n d F r a n k ( 5 ) . T h e results i n T a b l e I I a r e l i s t e d i n i n c r e a s i n g o r d e r o f μ v a l u e s , o r i n other w o r d s , d e c r e a s i n g solvent p o w e r . T h e t w o extremes i n this c o r r e l a t i o n are b e n z e n e a n d t h e ^-solvent c y c l o hexane.

T h e i n t r i n s i c viscosities l i s t e d i n t h e s e c o n d c o l u m n decrease

w i t h d e c r e a s i n g solvent p o w e r , w h i c h is a d i r e c t c o n s e q u e n c e o f t h e c o n t r a c t i o n of t h e s w o l l e n p o l y m e r c o i l w i t h d e c r e a s i n g solvent p o w e r (1, 29, 30). T h e same h o l d s t r u e f o r t h e exponent "d i n t h e M a r k - H o u w i n k 9

e q u a t i o n s h o w n i n t h e t h i r d c o l u m n , w h i c h decreases w i t h solvent p o w e r (1, 29, 30).

decreasing

T h e d i m e n s i o n s of t h e flexible p o l y s t y r e n e

m o l e c u l e s c a l c u l a t e d b y t h e F l o r y - F o x e q u a t i o n (7)

are l i s t e d i n t h e

f o u r t h c o l u m n . I t is e v i d e n t t h a t t h e d i m e n s i o n s of t h e p o l y s t y r e n e coils decrease w i t h d e c r e a s i n g solvent p o w e r , w h i c h , as w i l l b e s h o w n b e l o w , influences m a r k e d l y t h e a d s o r p t i o n of p o l y s t y r e n e at t h e s o l i d / l i q u i d interface. T h e q u a n t i t y ( < F > ) 2

1 / 2

reaches a m i n i m u m f o r t h e ^-solvent

w h e n t h e p o l y m e r forms a c o m p a c t c o i l . T h e a d s o r p t i o n isotherms of p o l y s t y r e n e - C o n G r a p h o n f r o m these 14

six solvents a r e p l o t t e d i n F i g u r e 1 i n terms of m g . P S - C a d s o r b e d p e r 1 4

g r a m G r a p h o n vs. c o n c e n t r a t i o n of s u p e r n a t a n t l i q u i d i n m g . P S - C p e r 1 4


5.

SCHICK

AND

m l . solution.

HARVEY,

67


JR.

T h e s o l u b i l i t y l i m i t p r e c l u d e d the s t u d y i n

cyclohexane

solutions (^-solvent) at e q u i l i b r i u m concentrations e x c e e d i n g 1 m g . / m l . T h e a d s o r p t i o n isotherms of these systems w i t h the e x c e p t i o n of d i o x a n e rise r a p i d l y to a p l a t e a u at 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 of a p p r o x i m a t e l y 1 m g . / m l . , as n o t e d g e n e r a l l y w i t h p o l y m e r s .


plateau level, however, have been observed. a d s o r p t i o n of power.

polystyrene- C 14

M a r k e d differences

in

These indicate increased

onto G r a p h o n w i t h

decreasing

solvent

T h e f o r m e r is expressed i n the fifth c o l u m n of T a b l e I I b y A — s

i.e., the e x t r a p o l a t e d s a t u r a t i o n c o n c e n t r a t i o n of the a d s o r p t i o n isotherms — a n d the latter b y the μ v a l u e . A s i m i l a r c o r r e l a t i o n has b e e n e s t a b l i s h e d b e t w e e n the degree o f a d s o r p t i o n a n d the h y d r o d y n a m i c properties. adsorption—i.e.,

A —increases w i t h decreasing 8

square length—i.e.,

{ ) ; see Table II.

α

2

1/2

m o l e c u l e s w i t h e v e r y segment a t t a c h e d to t h e surface sites of t h e n o n porous G r a p h o n .

I n this flat o r i e n t a t i o n t h e areas p e r m o n o m e r

decrease w i t h d e c r e a s i n g solvent p o w e r .

unit

O n l y for the good solvents—

i.e., b e n z e n e a n d t o l u e n e — w a s t h e o b s e r v e d area c o m p a r a b l e t o that of the m o n o m e r i c styrene. T h u s , i n g o o d solvents i t m a y b e a s s u m e d t h a t t h e p o l y m e r forms a r e l a t i v e l y flat a n d c o m p r e s s e d i n t e r f a c i a l l a y e r w i t h m a n y segments a t t a c h e d t o t h e s o l i d surface. A s e v i d e n c e d f r o m t h e large cross-sectional areas i n c o l u m n t w o , t h e s w o l l e n coils i n these g o o d solvents are p r o n e to u n c o i l to assume t h e c o n f o r m a t i o n suggested.

However,

this m o d e l is r u l e d o u t b y t h e r e l a t i v e l y m u c h s m a l l e r areas p e r m o n o m e r u n i t f o r t h e m e d i u m a n d p o o r solvents i n w h i c h t h e p o l y m e r forms t i g h t e r coils, viz., first c o l u m n . T h e alternate m o d e l is suggested f o r t h e m e d i u m a n d p o o r solvent systems i n w h i c h t h e p o l y m e r assumes a l o o p o r c o i l structure w i t h o n l y a f r a c t i o n of t h e p o l y m e r segments b e i n g a t t a c h e d t o t h e surface sites of t h e n o n p o r o u s G r a p h o n (26).

T h e s e c o n c l u s i o n s are

c o r r o b o r a t e d b y t h e d a t a l i s t e d i n t h e t h i r d c o l u m n . F r o m t h e better s o l vents less t h a n 6 χ

1 0 " grams p o l y s t y r e n e / c m . G r a p h o n w a s a d s o r b e d ; 8

2

w h e r e a s f r o m m e d i u m a n d p o o r solvents, f r o m 14.4 Χ 1 0 " to 19.5 Χ 1 0 8

grams/cm.

2

was adsorbed.

F r i s c h , H e l l m a n , a n d L u n d b e r g (10)

- 8

made

s i m i l a r observations f o r p o l y s t y r e n e a d s o r b i n g f r o m toluene onto c a r b o n (3 X 10" g r a m / c m . ) . 8

gram/cm.

2

2

A s i m p l e flat m o n o l a y e r r e q u i r e s o n l y 5 Χ 1 0

( 5 A . l a y e r i f p o l y m e r has d e n s i t y of 1) (9, 27).

- 8

Thus, the

a m o u n t a d s o r b e d i n a m e d i u m o r p o o r solvent m u s t b e m o r e t h a n a s i m p l e m o n o l a y e r . A s c i t e d a b o v e f o r these systems a m o n o l a y e r of coils w h i c h are a t t a c h e d to t h e surface w i t h o u t a n y a p p r e c i a b l e c h a n g e i n shape a n d b o n d e d to t h e surface b y o n l y a f e w p e r i p h e r a l m o n o m e r

u n i t s is a

p l a u s i b l e m o d e l (14, 21 ). S t e i n b e r g (25) has p r o p o s e d a m o d e l i n w h i c h the segment d e n s i t y i n t h e i n t e r f a c i a l l a y e r of a d s o r b e d p o l y m e r m o l e c u l e s p r o g r e s s i v e l y decreases as t h e distance f r o m t h e surface increases.


5.

SCHICK A N D

HARVEY,

JR.

69


Results r e p o r t e d i n T a b l e I I f o l l o w the p a t t e r n that a d s o r p t i o n of p o l y s t y r e n e - C o n G r a p h o n is f a v o r e d f r o m a poorer solvent. 14

Experi-

ments are r e p o r t e d here a n d i n the f o l l o w i n g p a r a g r a p h w h i c h h a v e b e e n p e r f o r m e d to test the r e v e r s i b i l i t y of this a d s o r p t i o n . W i t h this a i m i n mind, (1)

the d i s p l a c e m e n t of p o l y s t y r e n e - C f r o m G r a p h o n b y

the

14


o r i g i n a l solvent a n d ( 2 ) the stepwise a d s o r p t i o n f r o m different solvents w e r e s t u d i e d . T h e d a t a of T a b l e I V i m p l y t h a t n o a p p r e c i a b l e d e s o r p t i o n i n the o r i g i n a l solvent w a s o b s e r v e d w i t h a l l six solvent systems.

Once

a d s o r b e d f r o m a p a r t i c u l a r solvent, a c c o r d i n g to S t e i n b e r g ( 2 5 ) , p o l y m e r s d o not d e s o r b a p p r e c i a b l y i n t h a t solvent because the m u l t i p l i c i t y of a d s o r b i n g sites e n e r g e t i c a l l y favors a d s o r p t i o n , r e s u l t i n g i n v e r y s m a l l d e s o r p t i o n r a t e constants. Results for the stepwise a d s o r p t i o n of p o l y s t y r e n e - C o n G r a p h o n 14

f r o m different solvents are s h o w n i n T a b l e V .

I n the first t w o sets of

experiments, d a t a are g i v e n for a n o r i g i n a l c o n c e n t r a t i o n of 0.4 m g . p o l y s t y r e n e - C / m l . or 0.2 m g . / m l , r e s p e c t i v e l y , i n a l l three a d s o r p t i o n steps. 1 4

I n the s e c o n d set the o r i g i n a l concentrations i n step t w o or three c o r r e s p o n d to the supernatant l i q u i d c o n c e n t r a t i o n i n the p r e c e d i n g step. On

c h a n g i n g the e n v i r o n m e n t f r o m toluene to b u t a n o n e - 2

(the

poorer solvent) additional polymer was adsorbed. H o w e v e r , on reverting the e n v i r o n m e n t b a c k to toluene most of the a d d i t i o n a l p o l y m e r w a s desorbed.

It is w o r t h n o t i n g that i n the s e c o n d set of experiments the

final a n d o r i g i n a l systems w e r e almost a l i k e . T h e s e results m a y a g a i n b e q u a l i t a t i v e l y e x p l a i n e d i n terms of

changes i n area r e q u i r e d b y

the

p o l y m e r m o l e c u l e to a t t a c h itself at the s o l i d / l i q u i d interface. T h e a r e a Table IV. Effect of Solvent on the Desorption of Polystyrene- C from Graphon 14

Solvent

41

Benzene Benzene Toluene Toluene Dioxane Dioxane Butanone-2 Butanone-2 E t h y l acetate E t h y l acetate Cyclohexane Cyclohexane

Equil. Cone. mg. PS-^C/ml.

% wt. PS-**C Desorbed

0.27 0.18 0.19 0.13 0.183 0.136 0.31 0.20 0.31 0.21 0.51 0.32

0 2 0 0 0 0 0 0 0 0 0 0

"Experimental procedure: (1) 40-hr. agitation cycle, (2) replacement of 10 ml. of supernatant solution in dispersion by 10 ml. of fresh solvent, and ( 3 ) 40-hr. agitation cycle.


70

INTERACTION

O F LIQUIDS

A T SOLID

SUBSTRATES

Table V . Stepwise Adsorption of Polystyrene- C on Graphon from Different Solvents


14

Step

Orig. Cone. of P S - ^ C , mg./ml.

Solvent

1 2 3 1 2 3 1 2 3 1 2 3

0.4 0.4 0.4 0.2 0.2 0.2 0.4 0.22 0.08 0.2 0.07 0

Toluene Butanone-2 Toluene Toluene Butanone-2 Toluene Toluene Butanone-2 Toluene Toluene Butanone-2 Toluene

a

Amount Adsorbed (mg./gram) or Desorbed in Step 39 56 40 26 40 22 38 36 27 28 14 10

Total P S - ^ C Adsorbed (mg./gram) 39 95 55 26 66 44 38 74 47 28 42 32

ads. ads. des. ads. ads. des. ads. ads. des. ads. ads. des.

"Experimental procedure: (1) 40-hr. agitation cycle, (2) replacement of supernatant solution, (3) 40-hr. agitation cycle, etc. p e r segment decreases as t h e p o l y s t y r e n e is d e s o l v a t e d o n c h a n g i n g t h e e n v i r o n m e n t f r o m g o o d t o p o o r solvent, thus c r e a t i n g a d d i t i o n a l a v a i l a b l e surface.

I n c r e a s e d a d s o r p t i o n m a y take p l a c e o n these a d d i t i o n a l free

surface sites. T h e reverse h o l d s t r u e f o r changes of e n v i r o n m e n t f r o m p o o r t o g o o d solvent. I n s u m m a r y , i t is p o s t u l a t e d t h a t u n d e r c o n d i t i o n s of w e a k segmentsurface i n t e r a c t i o n a u n i f o r m l y a d s o r b i n g p o l y m e r l i k e p o l y s t y r e n e a t taches itself, i n t h e c o n c e n t r a t i o n regions r e p r e s e n t e d b y t h e p l a t e a u x i n t h e a d s o r p t i o n isotherms, t o t h e G r a p h o n surface f r o m g o o d solvents a p p r o a c h i n g a flat o r i e n t e d m o n o l a y e r .

I n contrast, f r o m a p o o r solvent

the p o l y m e r assumes a l o o p o r c o i l s t r u c t u r e i n w h i c h o n l y p a r t o f t h e p o l y m e r segments a r e a t t a c h e d d i r e c t l y t o t h e G r a p h o n surface.

Thus,

both models postulated are useful to describe the conformation of t h e adsorbed

polymer molecules

at t h e s o l i d interface w i t h

each

being

a p p l i c a b l e f o r different solvent m e d i a . Acknowledgment T h e authors a r e i n d e b t e d t o S . C a r a n g e l o f o r i n s t r u c t i o n i n t h e radiochemical techniques.

Literature Cited (1) Billmeyer, F. W., Jr., "Textbook of Polymer Chemistry, p. 32, Interscience, New York, 1962. (2) Binford, J. S., Gessler, A. M., J. Phys. Chem. 63, 1376 (1959).



5.

S C H I C K A N D H A R V E Y , JR.


71

(3) Boundy, R. H., Boyer, R. F., "Styrene," p. 344, Reinhold, New York, 1952. (4) Ibid., p. 390. (5) Breitenbach, J. W., Frank, H. P., Monats. Chem. 79, 531 (1948). (6) Ellerstein, S., Ullman, R., J. Polymer Sci. 55, 123 (1961). (7) Flory, P. J., Fox, T. G., Jr., J. Am. Chem. Soc. 73, 1904 (1951). (8) Fontana, B. J., Thomas, J. R., J. Phys. Chem. 65, 480 (1961). (9) Fowkes, F. M., "Treatise on Adhesion and Adhesives," Vol. 1, Chapt. 9, R. L. Patrick, ed., Marcel Dekker, New York, 1967. (10) Frisch, H. L., Hellman, M. Y., Lundberg, J. L., J. Polymer Sci. 38, 441 (1959). (11) Gilliland, E. R., Gutoff, Ε. B., J. Appl. Polymer Sci. 3, 26 (1960). (12) Hobden, J. F., Jellinek, H. H. G., J. Polymer Sci. 11, 365 (1953). (13) Hughes, R. E., von Frankenberg, C. Α., Ann. Rev. Phys. Chem. 14, 290 (1963). (14) Kipling, J. J., "Adsorption from Solutions of Nonelectrolytes," Chapt. 8, Academic Press, New York, 1965. (15) Kolthoff, I. M., Gutmacher, R. E., Kahn, Α., J. Phys. Chem. 55, 1240 (1951). (16) Koral, J., Ullman, R., Eirich, R. F., J. Phys. Chem. 62, 541 (1958). (17) Luce, J. E., Robertson, Α. Α., J. Polymer Sci. 51, 317 (1961). (18) Patat, F., Killman, E., Schliebener, C., Fortschr. Hochpolym. Forsch. 3, 332 (1964). (19) Patat, F., Killman, E., Schliebener, C., Rubber Chem. Technol. 39, 36 (1966). (20) Perkel, R., Ullman, R., J. Polymer Sci. 54, 127 (1961). (21) Rowland, F., Bulas, R., Rothstein, E., Eirich, F. R., Ind. Eng. Chem. 57, No. 9, 46 (1965). (22) Rowland, F. W., Eirich, F. R., J. Polymer Sci. Part A-1, 4, 2401 (1966). (23) Schick, M. J., Ph.D. Thesis, Polytechnic Institute of Brooklyn (1948). (24) Schick, M. J., Doty, P. M., Zimm, Β. H., J. Am. Chem. Soc. 72, 530 (1950). (25) Steinberg, G., J. Phys. Chem. 71, 292 (1967). (26) Stromberg, R. R., Tutas, D. J., Passaglia, E., J. Phys. Chem. 69, 3955 (1965). (27) Stromberg, R. R., "Treatise on Adhesion and Adhesives," Vol. 1, Chapt. 3, R. L. Patrick, ed., Marcel Dekker, New York, 1967. (28) Stromberg, R. R., Quasius, A. R., Toner, S. D., Parker, M. S., J. Res. Natl. Bur. Stds. 62, 71 (1959). (29) Tanford, C., "Physical Chemistry of Macromolecules," p. 400, John Wiley, New York, 1961. (30) Ibid., p. 408. RECEIVED October 26,

1967.


Solid Interface

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