Streaming Potential Studies on Gel-coated Glass Capillaries

18 Streaming Potential Studies on Gel-coated Glass Capillaries

Downloaded by PENNSYLVANIA STATE UNIV on June 7, 2013 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/bk-1976-0031.ch018

SHAO M. MA, DONALD E. GREGONIS, RICHARD VAN WAGENEN, and JOSEPH D. ANDRADE Department of Materials Science and Engineering, University of Utah, Salt Lake City, Utah 84112 The s e p a r a t i o n o f l i v i n g c e l l s i n z e r o g r a v i t y e n v i r o n m e n t s appears t o o f f e r s i g n i f i c a n t advantages o v e r analogous s e p a r a t i o n s on e a r t h . The z e r o g r a v i t y e n v i r o n m e n t e l i m i n a t e s s e d i m e n t a t i o n and d e n s i t y f l u c t u a t i o n p r o b l e m s . As d e m o n s t r a t e d i n A p o l l o 16 experiments a m a j o r p r o b l e m w i t h f r e e zone e l e c t r o p h o r e s i s i n a c l o s e d s y s t e m i s t h e d i f f e r e n t i a l f l u i d movement due t o t h e surface e l e c t r i c a l properties of the container (electroosmosis). As a c o n s e q u e n c e , t h e r e s o l u t i o n o f t h e s e p a r a t i o n and t h e a n a l y s i s i n v o l v e d a r e g r o s s l y compromised by t h e r e s u l t i n g " b u l l e t " shape f l o w p a t t e r n s . A s o l u t i o n t o t h i s problem i s t o produce s u r f a c e s w h i c h e x h i b i t e s s e n t i a l l y no e l e c t r o k i n e t i c p r o p e r t i e s when i n e q u i l i b r i u m w i t h t h e i r e n v i r o n m e n t . T h i s c a n be a c h i e v e d by n e u t r a l i z i n g t h e s u r f a c e c h a r g e o r by s h i f t i n g t h e h y d r o d y namic s h e a r p l a n e away f r o m t h e i n t e r f a c e by use o f h y d r o p h i l i c surface coatings. In t h i s s t u d y , g l a s s t u b e s were s u b j e c t e d t o v a r i o u s c o a t i n g s and s u r f a c e t r e a t m e n t s . In p a r t i c u l a r , i t was f e l t t h a t u n charged h y d r o p h i l i c m e t h a c r y l a t e polymer c o a t i n g s should decrease the e l e c t r o o s m o s i s . The o v e r a l l e f f e c t s o f t h e s e t r e a t m e n t s upon s t r e a m i n g p o t e n t i a l i s d i s c u s s e d . Apparatus The s t r e a m i n g p o t e n t i a l a p p a r a t u s has been d e s c r i b e d i n detail (2,3). I t i s an a l l - g l a s s s y s t e m u t i l i z i n g Ag/AgCl e l e c trodes. S t r e a m i n g f l u i d i s f o r c e d back and f o r t h f r o m one r e s e r v o i r t o the o t h e r through a g l a s s tube using p r e s s u r i z e d p u r e n i t r o g e n g a s . A g l a s s pH e l e c t r o d e and a t h e r m o m e t e r a r e p o s i t i o n e d i n one o f t h e r e s e r v o i r s . A K e i t h l e y model 616 d i g i t a l e l e c t r o m e t e r measures s t r e a m i n g p o t e n t i a l o r s t r e a m i n g current. A l l new and l a r g e g l a s s w a r e a r e c l e a n e d i n i t i a l l y i n c h r o m i c s u l f u r i c a c i d , thoroughly rinsed i n running, d i s t i l l e d water, soaked i n doubly d i s t i l l e d w a t e r , r e r i n s e d i n double d i s t i l l e d w a t e r and t h e n a i r d r i e d i n a d u s t - f r e e e n v i r o n m e n t . Small

241

In Hydrogels for Medical and Related Applications; Andrade, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1976.

242

HYDROGELS FOR MEDICAL AND RELATED APPLICATIONS

g l a s s w a r e i s c l e a n e d by r a d i o f r e q u e n c y glow d i s c h a r g e To c a r r y o u t t h e s t r e a m i n g p o t e n t i a l measurement e a c h r e s e r v o i r i s f i l l e d w i t h a b o u t 500 ml o f p h o s p h a t e b u f f e r a t pH 7.2 c o n t a i n i n g 0.01 M KC1. The e l e c t r o d e s a r e i n s e r t e d . The p o t e n t i a l i s t h e n measured as a f u n c t i o n o f d r i v i n g p r e s s u r e . The s t r e a m i n g p o t e n t i a l , E t , i s l i n e a r l y d e p e n d e n t on t h e p r e s s u r e d r o p , P, a c r o s s t h e t u b e , as g i v e n by ( 5 j s

r

_ 4πηΚ str " ~D ψ— where ζ i s t h e z e t a p o t e n t i a l , η and D a r e t h e v i s c o s i t y and d i e l e c t r i c constant, r e s p e c t i v e l y , i n the d i f f u s e p o r t i o n of the e l e c t r i c a l d o u b l e l a y e r , and Κ i s t h e b u l k s p e c i f i c c o n d u c t i v i t y of the e l e c t r o l y t e (assuming s u r f a c e conductance i s n e g l i g i b l e r e l a t i v e to bulk conductance). B a l l and F u e r s t e n a u (6) have r e v i e w e d t h e s t r e a m i n g p o t e n t i a l l i t e r a t u r e i n r e g a r d t o s t r e a m i n g p o t e n t i a l d a t a . They have c o n c l u d e d t h a t , due t o as y e t u n e x p l a i n e d f l o w and symmetry p o t e n t i a l s common t o a w i d e v a r i e t y o f e l e c t r o d e t y p e s , t h e slope of the l o c i of E ^ d a t a a t a number o f d r i v i n g p r e s s u r e s , P, i n o p p o s i t e f l o w d i r e c t i o n s , Δ Ε / Δ Ρ , s h o u l d be u t i l i z e d i n t h e above e q u a t i o n . T h i s has been t h e c a s e i n t h i s s t u d y . S t r e a m i n g p o t e n t i a l d a t a was o b t a i n e d by m e a s u r i n g s t r e a m i n g p o t e n t i a l s a t a d r i v i n g p r e s s u r e o f 2cm Hg, t h e n r e v e r s i n g t h e f l o w d i r e c t i o n and r e p e a t i n g t h e measurement. The d r i v i n g p r e s s u r e was i n c r e a s e d by 2cm Hg and s t r e a m i n g p o t e n t i a l s were a g a i n measured i n b o t h f l o w d i r e c t i o n s . T h i s p r o c e s s was r e p e a t e d u n t i l t h e d r i v i n g p r e s s u r e r e a c h e d 12cm Hg. The l o c i o f s t r e a m i n g p o t e n t i a l d a t a as a f u n c t i o n o f d r i v i n g p r e s s u r e were t h e n f i t t e d to a l i n e a r regression best f i t s t r a i g h t l i n e using a H e w l e t t P a c k a r d (Model 9820A) programmable c a l c u l a t o r . A b s o l u t e v a l u e s o f z e t a p o t e n t i a l c a l c u l a t e d f r o m t h e above e q u a t i o n may be e r r o n e o u s due t o a s s u m p t i o n s c o n c e r n i n g v a l u e s f o r d o u b l e l a y e r v i s c o s i t y , d i e l e c t r i c c o n s t a n t , and e n t r a n c e f l o w e f f e c t s r e s u l t i n g f r o m t h e l a r g e ID o f t h e t u b e s u t i l i z e d i n t h i s study (2,3). E

r


ζ

s

r

5 τ Γ

Materials T h i c k - w a l l e d " P y r e x " c a p i l l a r y t u b e s , a p p r o x i m a t e l y 0.2cm ID and 15cm l o n g , were u s e d . U n c o a t e d c a p i l l a r i e s had ΔΕ . /ΔΡ o f - 0 . 3 5 7 mV/cm Hg. D i f f e r e n t s i l a n e a d h e s i o n p r o m o t e r s (7) were used t o p r e t r e a t t h e g l a s s s u r f a c e s p r i o r t o g e l c o a t i n g . An i n v e s t i g a t i o n o f s e v e r a l s i l a n i z i n g r e a g e n t s u s i n g d i f f e r e n t p r o c e d u r e s showed a s l i g h t decrease in ΔΕ £ /ΔΡ f o r a l l the s i l a n e c o a t i n g s . The Δ Ε £ /ΔΡ v a l u e s were n o t s e n s i t i v e t o t h e o r g a n i c f u n c t i o n a l i t y o f trie s i l a n e . A v a r i e t y o f h y d r o p h i l i c p o l y m e r s were used as c o a t i n g m a t e r i a l s i n c l u d i n g m e t h y l c e l l u l o s e (Dow M e t h o c e l MC, p r e m i u m , s

5

Γ

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r

18.

MA ET AL.

Streaming

Potential

243

Studies

4000 c p s ) ; h y d r o x y p r o p y l m e t h y l c e l l u l o s e (Dow M e t h o c e l , 9 0 H g , premium, 15000 c p s ) ; d e x t r i n ( M a t h e s o n , Coleman and B e l l ) and agarose (Biorad L a b s ) . H y d r o x y e t h y l m e t h a c r y l a t e was d o n a t e d by Hydro Med S c i e n c e s , I n c . M e t h o x y e t h y l m e t h a c r y l a t e and m e t h o x y e t h o x y e t h y l m e t h a c r y l a t e were p r e p a r e d i n o u r l a b o r a t o r i e s by base c a t a l y z e d t r a n s e s t e r i f i c a t i o n o f m e t h y l m e t h a c r y l a t e with the corresponding alcohol ( 8 ) .


Methods

and R e s u l t s

The s i l a n e compounds were a p p l i e d u s i n g s t a n d a r d p r o c e d u r e s (6). A s i l a n e s o l u t i o n was r i n s e d t h r o u g h t h e t u b e s , f i r s t i n one d i r e c t i o n , t h e n i n t h e o t h e r , and t h e t u b e s were vacuum dried overnight. The s i l a n e compounds u s e d a n d t h e ΔΕ . /ΔΡ v a l u e s a r e g i v e n i n T a b l e I. TABLE ΔΕ^/ΔΡ

Values

I.

f o r Silane

Coatings s t r (mV/cm Hg) A

SSStina

E

M

P

1,1,1,3,3,3-hexamethyldisilazine:triethylamine -0.242 Chlorotrimethylsilane:triethylamine (1:1) -0.221 D i c h l o r o d i m e t h y l s i l a n e : t r i e t h y l ami ne ( 1 : 1 ) -0.253 γ - m e t h a c r y l o x y p r o p y l t r i m e t h o x y s i l a n e : t r i e t h y l ami ne ( 1 : 1 ) - 0 . 2 3 4 Y-glycidoxypropyltrimethoxysilane:triethylamine (1:1) -0.229 γ-glycidoxypropyltrimethoxysilane:n-propylami ne ( 1 : 1 ) -0.230 Y-glycidoxypropyltrimethoxysilane:pH 4 aq. a c e t i c acid -0.241 The Y - g l y c i d o x y p r o p y l t r i m e t h o x y s i l a n e : t r i e t h y l a m i n e ( 1 : 1 ) s i l a n e c o a t i n g was s e l e c t e d f o r f u r t h e r t r e a t m e n t w i t h t h e neutral polysaccharides. I t was t h o u g h t t h a t c o a t i n g t h e p o l y s a c c h a r i d e s upon t h e e p o x y - s i l a n i z e d g l a s s was e i t h e r an a c i d o r base c a t a l y z e d p r o c e s s r e s u l t i n g i n c o v a l e n t a t t a c h m e n t o f t h e polysaccharide to the surface (Figure 1 ) . S t a n d a r d s o l u t i o n s o f v a r i o u s p o l y s a c c h a r i d e s were p r e p a r e d by d i s s o l v i n g i n e i t h e r 0 . 5 % HC1 o r 0 . 5 % Κ0Η. I f t h e p o l y s a c c h a r i d e was s o l u b l e , t h e v i s c o s i t y o f t h e s o l u t i o n was " r e g u l a t e d " by t h e a d d i t i o n o f p o l y s a c c h a r i d e u n t i l i t had t h e c o n s i s t e n c y o f a t h i c k syrup. O t h e r w i s e t h e p o l y s a c c h a r i d e was added t o c o m p l e t e saturation. The p o l y s a c c h a r i d e s o l u t i o n was p u l l e d t h r o u g h t h e t u b e s i n each d i r e c t i o n by a w a t e r - a s p i r a t o r p a r t i a l vacuum. The t u b e s were t h e n p l a c e d i n a vacuum oven a t 120°C f o r 12 h o u r s , u n l e s s o t h e r w i s e s p e c i f i e d . The t u b e s were e x h a u s t i v e l y r i n s e d w i t h d i s t i l l e d w a t e r and t h e Δ Ε ^ / Δ Ρ v a l u e s were o b t a i n e d . C o n s i s t e n t l y l o w e r A E s t r M P v a l u e s were o b t a i n e d when t h e p o l y s a c c h a r i d e s were a p p l i e d i n a c i d i c s o l u t i o n as compared t o


244


a.

Acid Catalyzed

-CH -0-CH

-CH-CH

?

Process l L

CH -0-CH -CH-CH 2

2

HO-Cellulose

2

w


ο

OH

^Cellulose

O-Cellulose

-CH -0-CH -CH-CH -OH

-CH -0-CH -CH-CH -OH 2

b.

2

Base C a t a l y z e d

HO"

+

2

2

+ "O-Cellulose - v

HOH

2

+

"O-Cellulose

-CHg-O-CHg-ÇH-CHg-O-Cellulose

V

"0

-CH -0-CH -CH-CH -0-Cellulose 2

2

Process

HO-Cellulose

-CH -0-CH -CH-CH 2

2

2

2

2

,

H

+

OH

Figure 1. Reaction schemes for the attachment of polysacchardies to epoxy-silane surfaces. A , acid catalyzed; B, base catalyzed.


M A ET AL.

18.

Streaming

Potential

b a s i c s o l u t i o n ; h o w e v e r , when m e t h y l c e l l u l o s e i n d i s t i l l e d w a t e r was a p p l i e d t o t h e e p o x y - s i l a n i z e d g l a s s , a Δ Ε ς ^ / Δ Ρ v a l u e was o b t a i n e d comparable t o t h e r e s u l t s o b t a i n e d w i t h m e t h y l c e l l u l o s e i n a c i d s o l u t i o n . A t t h e moment t h e mechanism t h a t g o v e r n s attachment o f m e t h y l c e l l u l o s e t o t h e e p o x y - s i l a n i z e d g l a s s i s i n doubt. The t r e a t m e n t o f g l a s s s u r f a c e s w i t h j u s t m e t h y l c e l l u l o s e or γ-glycidoxypropyltrimethoxysilane does n o t g i v e t h e l o w ΔΕ ^ /ΔΡ values. T h i s phenomenon i s s t i l l b e i n g i n v e s t i g a t e d . F u r t h e r c o a t i n g o f m e t h y l c e l l u l o s e onto a m e t h y l c e l l u l o s e c o a t i n g showed no change i n Δ Ε * / Δ Ρ . The use o f 1 , 2 , 4 , 5 , 9 , 1 0 t r i e p o x y d e c a n e (TED) as a c r o s s l i n k e r i n t h e m e t h y l c e l l u l o s e s o l u t i o n s (5% TED i n 0 . 5 % H C 1 - m e t h y l c e l l u l o s e ) was i n v e s t i g a t e d . C u r i n g was a c c o m p l i s h e d b y h e a t i n g o v e r n i g h t a t 120°C i n vacuum. No s t a t i s t i c a l change was n o t e d f o r t h i s t r e a t m e n t o v e r normal m e t h y l c e l l u l o s e tubes (Table I I ) . 5

Γ

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245

Studies

TABLE

Γ

II.

E f f e c t s o f S i l a n e and P o l y s a c c h a r i d e C o a t i n g s

str (mV/cm Hg)

A

Coating (1) (2) (3) (4) (5) (6) (7) (8) (9)

(10) (11) (12)

Uncoated γ-glycidoxypropyltrimeth o x y s i l a n e : t r i e t h y l ami ne ( 1 : 1 ) P r o c e d u r e 2 , t h e n 0 . 5 % HC1 P r o c e d u r e 2 , t h e n 0 . 5 % KOH Methylcellulose in d i s t i l l e d Ο Procedure 2 , then m e t h y l c e l l u l o s e i n 0 . 5 % KOH Procedure 2, then m e t h y l c e l l u l o s e i n 0 . 5 % HC1 Procedure 2 , then m e t h y l c e l l u l o s e i n d i s t i l l e d H«0 M e t h y l c e l l u l o s e coated tubes ( P r o c e d u r e 7) r e c o a t e d w i t h m e t h y l c e l l u l o s e w i t h 5% 1 , 2 , 4 , 5 , 9 , 1 0 - t r i e p o x y d e c a n e on 0 . 5 % HC1 Procedure 2 , then h y d r o x y p r o p y l m e t h y l c e l l u l o s e i n 0 . 5 % HC1 Procedure 2 , then d e x t r i n i n 0 . 5 % HC1 Procedure 2 , then agarose i n 0 . 5 % HC1

Upon ΔΕ ^ /ΔΡ V a l u e s

E

/

A

P

Standard Deviation

-0.356

0.010

-0.310 -0.226 -0.261 -0.166

0.007

-0.130

0.012

-0.078

0.008

-0.058

0.002

-0.103

0.003

— —

0.090

-0.096 -0.245 -0.250



246


A simple water-polyfluorocarbon surface contact angle t e s t was used t o d e t e c t s u r f a c e - a c t i v e e x t r a c t a b l e s (9) f r o m t h e coated c a p i l l a r i e s . H i g h c o n t a c t a n g l e s were n o t e d w i t h a l l tubes. No s i g n i f i c a n t change i n t h e c o n t a c t a n g l e was e v i d e n t w i t h the methyl c e l l u l o s e - c o a t e d t u b e s , i n d i c a t i n g t h a t the m e t h y l c e l l u l o s e i s not r e a d i l y e x t r a c t e d from the s u r f a c e . To o b t a i n c a p i l l a r y t u b e s c o a t e d w i t h m e t h a c r y l a t e h y d r o g e l s , f i r s t s o l u b l e p o l y m e r s were p r e p a r e d . T h i s was a c c o m p l i s h e d by r a d i c a l i n i t i a t i o n o f t h e d e s i r e d monomer a t l o w d i l u t i o n (1 to 10, v/v) i n e t h a n o l . A s m a l l amount o f t h i s p o l y m e r s o l u t i o n i s a l l o w e d t o f l o w t h r o u g h t h e g l a s s c a p i l l a r y , and w i t h a l i t t l e c a r e and p a t i e n c e , a v e r y u n i f o r m c o a t o f t h e p o l y m e r c o u l d be d e p o s i t e d on t h e i n s i d e o f t h e c a p i l l a r y . T h e v i s c o s i t y o f t h e p o l y m e r s o l u t i o n was r e g u l a t e d by t h e a d d i t i o n o r e v a p o r a t i o n o f solvent. The t u b e s were c u r e d o v e r n i g h t a t 60°C and t h e n a l l o w e d to e q u i l i b r a t e i n d i s t i l l e d water. The monomers t h a t were i n v e s t i g a t e d were m e t h o x y e t h y l m e t h a c r y l a t e (MEMA), h y d r o x y e t h y l m e t h a c r y l a t e (HEMA) and m e t h o x y e t h o x y e t h y l m e t h a c r y l a t e (MEEMA). I t has been d e t e r m i n e d t h a t t h e s e p o l y m e r s s w e l l i n w a t e r t o i n c o r p o r a t e 3 . 5 % , 40% and 63% w a t e r , r e s p e c t i v e l y ( 9 ) . The c o r r e s p o n d i n g Δ Ε ^ / Δ Ρ v a l u e s are comparable to the best m e t h y l c e l l u l o s e values

TABLE

III).

III.

E f f e c t s of H y d r o p h i l i c Methacrylate Coatings

Coating

(Table

Upon Δ Ε _ / Δ Ρ

ΔΕ /ΔΡ /«χ//™ un\ (mV/cm Hg)

(1) U n c o a t e d t u b e s -0.290 (2) H y d r o x y e t h y l m e t h a c r y l a t e (HEMA) - 0 . 0 4 6 (3) M e t h o x y e t h y l m e t h a c r y l a t e (MEMA) - 0 . 0 5 8 (4) M e t h o x y e t h o x y e t h y l m e t h a c r y l a t e (MEEMA) -0.038 (5) HEMA w i t h 1% m e t h a c r y l i c a c i d (MAA) -0.080 (6) HEMA w i t h 3% MAA -0.100 (7) HEMA w i t h 10% MAA -0.113 (8) HEMA w i t h q u a t e r n i z e d 1% d i m e t h y l a m i n o e t h y l m e t h a c r y l a t e (DMAEMA) +0.070 (9) HEMA w i t h q u a t e r n i z e d 3% DMAEMA +0.074 (10) HEMA w i t h q u a t e r n i z e d 10% DMAEMA +0.087

$1

Values

Γ

Standard . j D

e

v

a

t

i

0.045 0.029 0.050 0.012 0.024 0.024 0.035 0.02* 0.004 0.014


o

n

18.

MA ET AL.

Streaming

247

Studies

To o b s e r v e t h e e f f e c t t h a t c h a r g e d g r o u p s i n t h e h y d r o p h i l i c p o l y m e r s had upon Δ Ε ^ / Δ Ρ v a l u e s , HEMA was p o l y m e r i z e d a t l o w d i l u t i o n w i t h v a r i o u s amounts o f m e t h a c r y l i c a c i d (MAA) and d i m e t h y l a m i n o e t h y l m e t h a c r y l a t e (DMAEMA). In t h e s t r e a m i n g s o l u t i o n b u f f e r e d t o pH 7 . 2 , m e t h a c r y l i c a c i d e x i s t s as t h e c h a r g e d s a l t , b u t d i m e t h y l a m i n o e t h y l m e t h a c r y l a t e e x i s t s as an u n c h a r g e d s p e c i e s . After polymerization of t h e HEMA-DMAEMA c o p o l y m e r , m e t h y l i o d i d e was added t o t h e p o l y m e r s o l u t i o n t o r e a c t w i t h t h e f r e e amino g r o u p s f o r m i n g q u a t e r n a r y ammonium i o d i d e s ( F i g u r e 2 ) . The c a p i l l a r y t u b e s were c o a t e d a s d e s c r i b e d f o r t h e o t h e r m e t h a c r y l a t e p o l y m e r s , c u r e d a t 60°C o v e r n i g h t and t h e n a l l o w e d t o s w e l l t o e q u i l i b r i u m i n e i t h e r d i s t i l l e d water o r streaming p o t e n t i a l b u f f e r . The MAA-HEMA c o p o l y m e r c o a t i n g s e x h i b i t e d a v e r a g e AE t /àP values which i n c r e a s e d n e g a t i v e l y w i t h i n c r e a s i n g percentage o f m e t h a c r y l i c a c i d i n t h e polymer: - 0 . 0 8 0 f o r 1% MAA, - 0 . 1 0 0 f o r 3% MAA, and - 0 . 1 1 3 f o r 10% MAA. The q u a t e r n a r y DMAEMA-HEMA copolymer coatings produced a n e t p o s i t i v e e l e c t r o k i n e t i c s u r f a c e as i n d i c a t e d by i n c r e a s i n g l y p o s i t i v e Δ Ε ~ ^ / Δ Ρ v a l u e s w i t h i n c r e a s i n g p e r c e n t a g e o f DMAEMA; +0.070 t o r 1% DMAEMA, +0.074 f o r 3% DMAEMA, and +0.087 f o r 10% DMAEMA ( T a b l e I I I ) . 5


Potential

Γ

s

r

Γ

Discussion A c c o r d i n g t o B r o o k ' s model ( 1 0 ) t h e z e t a p o t e n t i a l i n t h e p r e s e n c e o f a d s o r b e d p o l y m e r ( h y d r o p h i l i c , u n c h a r g e d ) c o u l d be h i g h e r o r l o w e r than t h a t i n t h e absence o f polymer. The e f f e c t depends on t h e r e l a t i v e m a g n i t u d e o f 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 p o l y m e r l a y e r , d , and t h e t h i c k n e s s , d , w i t h i n w h i c h n o n z e r o f l u i d f l o w o c c u r s d u r i n g an e l e c t r o k i n e t i c e x p e r i m e n t . T h r e e a r e a s have been c i t e d : f

1.

2.

F o r a t o t a l l y f r e e d r a i n i n g adsorbed l a y e r , t h e l o c a t i o n o f t h e s h e a r p l a n e i s u n a f f e c t e d by t h e p r e s e n c e o f t h e adsorbed l a y e r , i . e . d = d . In t h i s c a s e , polymer adsorp t i o n c a u s e s an i n c r e a s e i n ' z e t a p o t e n t i a l . F o r a p a r t i a l l y f r e e d r a i n i n g adsorbed l a y e r , t h e shear plane i s s h i f t e d t o a p o s i t i o n w i t h i n t h e adsorbed polymer l a y e r (0 < d < d ) . I n t h i s c a s e p o l y m e r a d s o r p t i o n may c a u s e e i t h e r an i n c r e a s e o r a d e c r e a s e i n z e t a p o t e n t i a l . When f l o w i s t o t a l l y e x c l u d e d f r o m t h e a d s o r b e d l a y e r , i . e . , the shear plane i s s h i f t e d o u t s i d e t h e adsorbed l a y e r (df = 0 ) , polymer a d s o r p t i o n causes a decrease i n z e t a potential. f

3.

Our d a t a was o b t a i n e d f r o m a l a r g e v a r i e t y o f n e u t r a l p o l y mer c o a t i n g s ; a l l show a d e c r e a s e i n ΔΕ +.~/ΔΡ. Our n e u t r a l p o l y m e r c o a t i n g s were c a s t on g l a s s c a p i l l a r y s u r f a c e s and a r e t h i c k e r t h a n t h o s e o b t a i n e d by a d s o r p t i o n . A l t h o u g h one c a n n o t d i r e c t l y compare o u r c o a t i n g s w i t h t h e t h r e e c a s e s p r e s e n t e d b y §

C o - , ; . •·•·,

·; -

:

In Hydrogels for Medical and Related Applications; Andrade, J.; ACS Symposium Series; American Chemical Washington, DC, 1976. Washi^iei, D. C.Society: 2003 6


248


M A A - H E M A COPOLYMER

DMAEMA-HEMA COPOLYMER

°7

O-7 £~0H

/ - O H

Oy

Oy

/-N-CH

3

^ O H

QUATERNIZED HEMA

CH r 3

Figure 2.

Charged groups introduced into the HEMA

DMAEMA

COPOLYMER

polymer


18.

Streaming

MA ET AL.

Potential

249

Studies

B r o o k ' s ( 1 0 ) i t does a p p e a r t h a t i n o u r c a s e t h e s h e a r p l a n e has been s h i f t e d f a r away f r o m t h e i n t e r f a c e . C o n s i d e r t h e Δ Ε £ / Δ Ρ values given i n Table I I I f o r p o s i t i v e o r n e g a t i v e groups c o p o l y m e r i z e d w i t h HEMA. A t l o w s t r e a m i n g p o t e n t i a l v a l u e s , i n c r e a s e d e x p e r i m e n t a l e r r o r i s i n t r o d u c e d i n t o the measurements. A t a g i v e n P, E ^ changes w i t h t i m e , p a r t l y due t o a change i n t h e r e l a t i v e f l u i d l e v e l s i n t h e two r e s e r v o i r s w h i c h c a u s e s a change i n Ρ a n d p a r t l y due t o e l e c t r o d e d r i f t w i t h t i m e o f unknown c a u s e ( 2 - 3 ) . I t was o b s e r v e d t h a t t h e Δ Ε £ r e a d i n g s were more s t a b l e f o r s u r f a c e s w i t h h i g h s t r e a m i n g p o t e n t i a l s . As a c o n s e q u e n c e , t h e e r r o r i s l a r g e r when t h e a b s o l u t e Δ Ε ^ / Δ Ρ v a l u e i s s m a l l . A l t h o u g h d i f f e r e n t samples o f s i m i l a r c o a t i n g o r t h e same sample measured on d i f f e r e n t days do show l a r g e v a r i a t i o n s i n t h e i r Δ Ε ^ / Δ Ρ v a l u e s , when t h e same sample was measured t h r e e t i m e s w i t h i n a s h o r t p e r i o d , i t s Δ Ε ^ / Δ Ρ v a l u e was quite consistent. A l s o , i n each s e r i e s o f m e a s u r e m e n t s , t h e ΔΕ 4- /ΔΡ v a l u e f o r s a m p l e s 5 - 1 0 f o l l o w e d t h e same t r e n d as g i v e n i n t a b l e I I I . T h e r e f o r e , we w o u l d l i k e t o a t t r i b u t e t h e l a r g e standard d e v i a t i o n values t o the v a r i a t i o n s i n experimental c o n d i t i o n s , s u r f a c e r o u g h n e s s , uneven c o a t i n g s , e t c . , and c o n s i d e r the e f f e c t o f i n c r e a s i n g a b s o l u t e streaming p o t e n t i a l values w i t h i n c r e a s i n g charge as r e a l . δ

s

r


$

Γ

δ

$

Γ

Γ

Γ

Conclusions A decrease i n Δ Ε ^ / Δ Ρ

o c c u r s when t h e g l a s s s u r f a c e i s

s i l a n i z e d o r c o a t e d w i t h a n e u t r a l p o l y s a c c h a r i d e such as methylcellulose. S i l a n i z a t i o n f o l l o w e d by m e t h y l c e l l u l o s e t r e a t m e n t g i v e s an a l m o s t t e n - f o l d d e c r e a s e i n Δ Ε ^ / Δ Ρ o v e r uncoated " P y r e x " g l a s s . Both a c i d a n d n e u t r a l m e t h y l c e l l u l o s e s o l u t i o n s c o a t e d upon a γ - g l y c i d o x y D r o p y l t r i m e t h o x y s i l a n e base gives the lowest Δ Ε ^ / Δ Ρ values f o r the polysaccharides examined. B a s e - c o n t a i n i n g m e t h y l c e l l u l o s e d e p o s i t e d on a γ-glycidoxypropyltrimethoxysilane surface gives s l i g h t l y higher ΔΕ ^ /ΔΡ v a l u e s , p e r h a p s due t o t h e c o r r o s i v e a c t i o n o f t h e b a s e . No a d d i t i o n a l improvement i n Δ Ε ^ / Δ Ρ v a l u e s was o b t a i n e d when the m e t h y l c e l l u l o s e tubes a r e recoated w i t h m e t h y l c e l l u l o s e containing a crosslinker. H y d r o p h i l i c m e t h a c r y l a t e polymer c o a t i n g s a l s o lower Δ Ε ^ / Δ Ρ values about t e n - f o l d over u n t r e a t e d g l a s s c a p i l l a r i e s . $

Γ

By added q u a t e r n a r y ammonium g r o u p s t o t h e s e p o l y m e r c o a t i n g s , t h e s i g n o f ΔΕ /ΔΡ i s changed f r o m n e g a t i v e t o p o s i t i v e . It t

i s f e l t t h a t by a d j u s t i n g t h e amount o f c h a r g e d co-monomers, a z e r o Δ Ε 7 Δ Ρ v a l u e c o u l d be o b t a i n e d . 0 + ν


250


Acknowledgements T h i s work has been s u p p o r t e d by t h e U. S. N a t i o n a l A e r o n a u t i c s and Space A d m i n i s t r a t i o n , M a r s h a l l Space F l i g h t C e n t e r , H u n t s v i l l e , A l a b a m a , u n d e r C o n t r a c t No, 8 - 3 0 2 5 3 , D r . J . Patterson, Contract Monitor. The a s s i s t a n c e o f R. Middaugh i s g r a t e f u l l y acknowledged.


Abstract Streaming potential techniques were used to measure the interfacial electrical potential of glass capillaries. Different silanizing reagents were used to coat the glass capillaries and decrease the streaming potential values by a comparable amount, i.e., about half that of the uncoated glass capillaries. A ten-fold decrease in streaming potential is observed when methyl cellulose is coated onto a γ-glycidoxypropyl silanized glass capillary. A comparable decrease is noted when hydroxyethyl methacrylate (HEMA), methoxyethyl methacrylate (MEMA) and methoxyethoxyethyl methacrylate (MEEMA) polymers are coated on the glass capillary. By adding anionic or cationic charged groups to the poly-HEMA coating, streaming potential values of opposite sign are obtained. Increasing the amount of methacrylic acid copolymerized with the HEMA monomer negatively increases the average ΔE /ΔP values. Increasing the amount of quaternized dimethyl aminoethyl methacrylate in the copolymer positively increases the average ΔE /ΔP values. str

str

Literature Cited 1. Snyder, R. S., Bier, M., Griffin, R. N., Johnson, A. J., Leidheiser, Jr., H., Micale, F. J., Vanderhoff, J. W., Ross, S., van Oss, C. J., Sep. Purific. Methods (1973) 2 (2), 259. 2. Van Wagenen, R., Ph.D. Dissertation, University of Utah, September 1975. 3. Van Wagenen, R., Andrade, J. D., and Hibbs, J. B., Jr., Submitted to J. Electrochem. Soc. 4. Hollahan, J. R., and Bell, A. T., Eds., "Techniques and Applications of Plasma Chemistry," Wiley, New York, 1974. 5. Davies, J. T., and Rideal, Ε. K., "Interfacial Phenomena," 2nd Ed., Academic Press, 1963. 6. Ball, B., and Fuerstenau, D. W., Miner. Sci. Eng., (1973) 5, 267. 7. Bascom, W. D., Macromolecules (1972) 5, 792. 8. Gregonis, D. E., Chen, C. Μ., and Andrade, J. D., "The Chemistry of Some Selected Methacrylate Hydrogels," this symposium.


18.

MA ET AL.

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Potential

Studies

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9. Baier, R. E., Gott, V. L., and Feruse, Α., Trans. Amer. Soc. Artificial Internal Organs (1970) 16, 50. 10. Brooks, D. Ε., J. Colloid and Interface Science, (1973) 43, 687.


Streaming Potential Studies on Gel-coated Glass Capillaries

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