Coulombic Interactions in Macromolecular Systems - American

13 Microstructure of Organic Ionic Membranes M . Pinéri

Downloaded by YORK UNIV on June 2, 2018 | https://pubs.acs.org Publication Date: March 28, 1986 | doi: 10.1021/bk-1986-0302.ch013

Groupe de Physico-Chimie Moléculaire, Département de Recherche Fondamentale, Service de Physique, Centre d'Etudes Nucléaires de Grenoble, 85 X , 38041 Grenoble Cédex, France

Perm selectivity and ionic conductivity are the two important parameters, besides the mechanical and chemical stability, to be considered in applications for ion exchange membranes; no connection is usually done with the microstructure. The aim of this paper is to present results on the physical structure of perfluorinated membranes. Crystallinity and distribution of the ionic sites across the thickness will be first considered. Evidence of a separate ionic phase will then be given and the local ion concentration will be analyzed. The p h y s i c a l s t r u c t u r e of i o n - c o n t a i n i n g polymers has been the s u b j e c t o f many i n v e s t i g a t i o n s . Each of t h e s e polymers has a h y d r o genated o r f l u o r i n a t e d backbone w i t h a s t a t i s t i c a l d i s t r i b u t i o n a l o n g t h e c h a i n o f the i o n exchange s i d e g r o u p s . The p e r c e n t a g e o f monomers c o n t a i n i n g the i o n i c groups i s u s u a l l y lower t h a n a. 10%; a t l a r g e r c o n c e n t r a t i o n s the copolymers may become w a t e r s o l u b l e . Exchange o f the c a r b o x y l i c o r s u l f o n i c a c i d p r o t o n s w i t h o t h e r c a t i o n s a l l o w s the use o f a l a r g e range of s p e c t r o s c o p i c t e c h n i q u e s to b e t t e r u n d e r s t a n d the m i c r o s t r u c t u r e of t h e s e m a t e r i a l s . Condens a t i o n o f charges has been t h e o r e t i c a l l y p r o p o s e d and a l s o experiment a l l y o b s e r v e d . The b a s i c i o n p a i r s A""X a r e f i r s t a s s o c i a t e d to form the s o - c a l l e d m u l t i p l e t s , w h i c h c o n t a i n a s m a l l number o f t h e s e ion pairs. E l e c t r i c i n t e r a c t i o n s a r e r e s p o n s i b l e f o r t h e s e aggregat i o n s and s t e r i c h i n d r a n c e l i m i t s the e x t e n t o f a s s o c i a t i o n . Cluster i n g of m u l t i p l e t s may o c c u r because of r e s i d u a l e l e c t r i c i n t e r a c t i o n s between m u l t i p l e t s . The p h y s i c a l c r o s s l i n k i n g g i v e s some i n t e r e s t i n g p r o p e r t i e s to t h e s e m a t e r i a l s . P o l y m e r i c i o n exchange membranes a r e a p a r t i c u l a r c l a s s o f t h e s e i o n - c o n t a i n i n g polymers. We have been i n t e r e s t e d i n u n d e r s t a n d i n g t h e i r m i c r o s t r u c t u r e i n o r d e r t o e x p l a i n membrane c h a r a c t e r i s t i c s such as p e r m s e l e c t i v i t y , i o n i c c o n d u c t i v i t y , and water d i f f u s i o n . Most of the r e s u l t s o b t a i n e d on p e r f l u o r i n a t e d ionomer membranes are summarized i n a book (i). In t h i s paper, we w i l l r e p o r t r e s u l t s m a i n l y o b t a i n e d on p e r f l u o r i n a t e d s u l f o n a t e d membranes. F i r s t , we w i l l show t h a t the d i s t r i b u t i o n of the i o n exchange groups may be q u i t e n o n u n i f o r m on +

0097-6156/ 86/ 0302-0159S06.00/ 0 © 1986 American Chemical Society

Eisenberg and Bailey; Coulombic Interactions in Macromolecular Systems ACS Symposium Series; American Chemical Society: Washington, DC, 1986.

C O U L O M B I C INTERACTIONS IN M A C R O M O L E C U L A R S Y S T E M S

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b o t h a m a c r o s c o p i c and a m i c r o s c o p i c l e v e l . We w i l l t h e n c o n c e n t r a t e on t h e s o - c a l l e d i o n i c r e g i o n s f o r w h i c h we w i l l d e f i n e t h e c h e m i c a l composition. The geometry o f t h e s e domains w i l l t h e n be d i s c u s s e d .


Crystallinity I n terms o f s t r u c t u r e o f t h e membranes the f i r s t p o i n t t o be d i s c u s sed c o n c e r n s the p o s s i b i l i t y o f h a v i n g c r y s t a l l i n e domains and t h e r o l e o f t h e s e domains. X r a y and d i f f e r e n t i a l s c a n n i n g c a l o r i m e t r y measurements a r e the b e s t ways t o probe t h e e x i s t e n c e and t h e s t r u c t u r e o f c r y s t a l l i n e domains. Figure 1 represents d i f f e r e n t X ray s c a t t e r i n g curves obtained f o r : • a low d e n s i t y p o l y e t h y l e n e a f t e r i r r a d i a t i o n g r a f t i n g w i t h s t y r e n e f o l l o w e d by s u l f o n a t i o n (1.46 meq/g exchange c a p a c i t y ) ( f i g u r e 1 a ) ; • a f l u o r i n a t e d p o l y v i n y l i d e n e on which have been i r r a d i a t i o n g r a f t e d monomers o f d i m e t h y l amino e t h y l m e t h a c r y l a t e f o l l o w e d by q u a t e r n i z a t i o n ( f i g u r e 1b). T h i s membrane i s a n i o n i c , t h e f o r m u l a i s : CH

3

-(CH -CF )-CH -C 2

2

2

0

H

-

C-O-(CH ) -NH-CH CH 0 2

2

3

I I

3

Indexes o f c r y s t a l l i n i t y c a n be o b t a i n e d from t h e s e d i f f e r e n t experiments. I t has t o be n o t e d t h a t t h e c r y s t a l l i n e s t r u c t u r e gene r a l l y c o r r e s p o n d s t o t h e c r y s t a l l i n e s t r u c t u r e o f t h e s t a r t i n g homopolymers. The c r y s t a l l i n e domains p l a y a r o l e as p h y s i c a l c r o s s l i n k s , A s i m i l a r b e h a v i o r has a l s o been o b s e r v e d i n membranes o b t a i n e d by c o p o l y m e r i z a t i o n . Many r e c e n t p e r f l u o r i n a t e d s u l f o n a t e d membranes have been o b t a i n e d by c o p o l y m e r i z a t i o n o f t e t r a f l u o r o e t h y l e n e w i t h a sulfonyl fluoride v i n y l ether. T h i s h i g h m o l e c u l a r weight polymer has t h e f o l l o w i n g f o r m u l a : - ( CF 2-CF )-CF 2-CF-0-CF 2-CF0-( CF 2 ) 2-S0 2 F 2

n

I

I CF

3

I n such a form t h i s m a t e r i a l i s m e l t f a b r i c a b l e and a f t e r h y d r o l y s i s i s c o n v e r t e d t o a i o n exchange membrane w i t h a p e r f l u o r o s u l f o n a t e group, - S 0 N a . The sodium c o u n t e r i o n c a n be exchanged by o t h e r metal i o n o r hydrogen i o n . F i g u r e 2 r e p r e s e n t s t h e n e u t r o n d i f f r a c t i o n spectrum o b t a i n e d w i t h a copolymer c o r r e s p o n d i n g t o η *\j 7. The e x i s t e n c e o f c r y s t a l l i ne domains w i t h t h e same s t r u c t u r e as f o r PTFE i m p l i e s t h e absence o f i o n exchange groups i n t h e s e domains. Such a r e s u l t i n v o l v e s t h e p r e s e n c e a l o n g t h e backbone o f many l o n g segments c o n t a i n i n g o n l y CF -CF2. A f t e r s w e l l i n g t h e b r o a d peak i s s i g n i f i c a n t l y b r o a d e r f o r the wet sample than f o r t h e d r y sample; t h i s o b s e r v a t i o n means t h a t the wet m a t e r i a l i s more d i s o r d e r e d and t h a t t h e s e p a r a t i o n between amorphous and c r y s t a l l i n e r e g i o n s i s l e s s c l e a r c u t . T h i s r e s u l t i m p l i e s t h a t t h e c r y s t a l l i t e s w h i c h a c t as p h y s i c a l c r o s s l i n k s a r e 3

2



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Figure 1. X-ray s c a t t e r i n g s p e c t r a o f membranes o b t a i n e d trom e t h y l e n e (a) and p o l y v i n y l i d e n e f l u o r i d e ( b ) .

0

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Figure 2. Neutron d i f f r a c t i o n s p e c t r a o f a c i d N a f i o n membrane f o r wet and d r v samples. Instrument i s D 1B. I n c i d e n t w a v e - l e n g t h i s λο = 2.56 A. The h o r i z o n t a l a x i s i s e x p r e s s e d e i t h e r i n s c a t t e r i n g a n g l e s (2Θ) u n i t s , o r i n n e u t r o n momentum t r a n s f e r (Q = ^ττ/λο ^- ^) units. Note the d i f f e r e n t v e r t i c a l s c a l e s f o r t h e two samples. The s e p a r a t i o n between t h e amorphous and c r y s t a l l i n e c o n t r i b u t i o n s t o the l a r g e a n g l e peak i s shown f o r the d r y sample. Temperature ^ 25°C. Reproduced w i t h p e r m i s s i o n from Ref. 3. C o p y r i g h t 1982 J . Polym. Sci., Polym. Phys. s


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p a r t i a l l y d e s t r o y e d by the c h a i n t e n s i o n s due t o s w e l l i n g o f t h e i o n i c h y d r o p h i l i c phase. These c r y s t a l l i t e s t h e r e f o r e form a s e p a r a t e phase and do not p a r t i c i p a t e i n the exchange p r o c e s s . M a c r o s c o p i c D i s t r i b u t i o n o f t h e I o n Exchange S i t e s a c r o s s Membrane T h i c k n e s s

the

An e l e c t r o n m i c r o p r o b e i s used t o d e f i n e the e x t e n t o f t h e homogenei t y f o r t h e d i s t r i b u t i o n of the exchange s i t e s a c r o s s t h e t h i c k n e s s o f the membrane. C a t i o n i c membranes a r e exchanged w i t h C u . Chlorhyd r a t i o n o f q u a t e r n i z e d Ν o f a n i o n i c membranes r e s u l t s from the p r e s e n c e of a CI i o n p e r i o n i c s i t e . The sample i s bombarded w i t h a beam o f e l e c t r o n s and the number of e m i t t e d X r a y s i n a c e r t a i n ener gy range ( c o r r e s p o n d i n g to t h e Cu and CI t r a n s i t i o n s ) i s counted. The number o b s e r v e d i s p r o p o r t i o n a l to t h e r e l e v a n t e l e m e n t a l concen tration. About 1 urn o f sample i s p r o b e d . The e l e c t r o n gun and X r a y d e t e c t o r a r e s i m u l t a n e o u s l y swept a t c o n s t a n t speed a c r o s s the edge 250 urn t h i c k ) of a cut membrane g i v i n g a p r o f i l e o f e l e m e n t a l c o n c e n t r a t i o n v e r s u s d i s t a n c e i n t o the membrane.


+ +

3

C o n c e n t r a t i o n p r o f i l e s o b t a i n e d w i t h d i f f e r e n t membranes a r e shown i n F i g u r e 3. Most o f t h e s e membranes o b t a i n e d by i r r a d i a t i o n g r a f t i n g have a nonhomogeneous d i s t r i b u t i o n o f i o n i c s i t e s a c r o s s t h e thickness. The exchange p r o p e r t i e s and the i o n i c c o n d u c t i v i t y must s t r o n g l y depend on t h i s asymmetry i n the r e p a r t i t i o n . A new a p p r o a c h to asymmetric membranes may be e n v i s a g e d from t h i s i r r a d i a t i o n g r a f t i n g technique. On the o t h e r hand, a homogeneous d i s t r i b u t i o n i s o b t a i n e d f o r the N a f i o n p e r f l u o r i n a t e d membranes o b t a i n e d by c o p o l y m e r i z a t i o n and h y d r o l y s i s o f t h e S 0 F s i d e groups. L e t us now c o n c e n t r a t e on t h e s e l a s t membranes, w h i c h have a r e l a t i v e l y homogeneous i o n i c s i t e d i s t r i b u t i o n a t a urn s c a l e . N a f i o n 1200 e q u i v a l e n t w e i g h t s have been s t u d i e d h e r e . We a l r e a d y know t h a t t h e r e a r e s m a l l m i c r o c r y s t a l l i t e s w i t h a PTFE s t r u c t u r e . The ques t i o n now concerns the d i s t r i b u t i o n o f SO3H o u t s i d e o f t h e s e c r y s t a l s ; do we have a s t a t i s t i c a l d i s t r i b u t i o n o f them o r do we have some i o n i c clusters with a larger i o n i c concentration? This question w i l l be d e v e l o p e d i n the next c h a p t e r . 2


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Microstructure of Organic ionic Membranes

Microscopic D i s t r i b u t i o n of the Ionic

Sites

I n f o r m a t i o n c o n c e r n i n g phase s e p a r a t i o n i n s i d e a m a t e r i a l c a n be o b t a i n e d from s m a l l a n g l e X r a y o r n e u t r o n s c a t t e r i n g . We have ex p e r i m e n t e d w i t h m e l t quenched p e r f l u o r i n a t e d membranes t o get r i d o f the c r y s t a l l i n e phase (2). Water a b s o r p t i o n a t room temperature i s s i m i l a r to t h a t i n t h e nonquenched m a t e r i a l . Water has been shown to be a b s o r b e d s p e c i f i c a l l y where t h e SO^H"" groups a r e i n t h e a c i d form; the w a t e r tends t o f i r s t s u r r o u n d t h e c a t i o n . Water p r o t o n s c o n s t i t u t e an e x c e l l e n t probe i n n e u t r o n s c a t t e r i n g because o f t h e l a r g e d i f f e r e n c e s i n s c a t t e r i n g l e n g t h compared w i t h C, F, S and 0. W i t h s m a l l a n g l e n e u t r o n s c a t t e r i n g (SANS), i t i s t h e r e f o r e p o s s i b l e to d e t e r m i n e i f t h e r e i s a s t a t i s t i c a l d i s t r i b u t i o n o f the h y d r a t e d i o n i c groups o r a c l u s t e r i n g o f them. 1


+

F i g u r e 4 shows t h e SANS c u r v e o b t a i n e d f o r a Na exchanged N a f i o n 1200 specimen f i r s t quenched from t h e m e l t and t h e n b o i l e d i n water. The water c o n t e n t f o r t h i s sample i s around 2 0 ^ b y w e i g h t o r 40% by volume. The e x i s t e n c e o f a peak a t low Q (Q = -τ- s i n 9 ) and a zero order s c a t t e r i n g i n c r e a s e i n the f i r s t evidence or a nonuniform d i s t r i b u t i o n o f water i n s i d e t h e specimen. S i m i l a r c u r v e s have been o b t a i n e d w i t h samples c o n t a i n i n g l e s s water ( 3 ) . When t h e h y d r a t i o n l e v e l i s d e c r e a s e d , we o b s e r v e d a d e c r e a s e i n t h e i n t e n s i t y o f the peak and a s h i f t a t h i g h e r a n g l e s o f t h i s peak. The q u a l i t a t i v e r e s u l t o b t a i n e d from t h e s e c u r v e s i s t h e e x i s t e n c e o f i o n i c h y d r o p h i l i c domains whose s i z e and d i s t a n c e may depend on t h e t o t a l w a t e r content. A more q u a n t i t a t i v e a n a l y s i s o f t h e e x t e n t o f phase s e p a r a t i o n may be o b t a i n e d by u s i n g the t e c h n i q u e o f i s o t o p i c r e p l a c e m e n t . Two samples a r e p r e p a r e d h a v i n g t h e same s t r u c t u r e except t h a t the atoms o f an element found i n one sample have been r e p l a c e d by an i s o t o p e i n the o t h e r . I n t h i s work, t h i s i s a c c o m p l i s h e d by h y d r a t i n g sam p l e s w i t h m i x t u r e s o f H 0 and D 0 o f v a r i o u s p r o p o r t i o n s . F o r samples t h a t have two phase s t r u c t u r e s t h e r a t i o o f SANS i n t e n s i t i e s i s g i v e n by: 2

2

_

I»(q) W

"

(A

2

"

(P2/P1

[Bi -

3 ] 2

(P2/Pi)B ] 2

2

where primed q u a n t i t i e s a r e t h o s e a f t e r i s o t o p i c r e p l a c e m e n t . The i n t e n s i t y r a t i o i s independent o f the s c a t t e r i n g v e c t o r and t h e two s c a t t e r i n g c u r v e s d i f f e r o n l y by a c o n s t a n t m u l t i p l e . F o r systems i n v o l v i n g more t h a n two phases t h i s w i l l not g e n e r a l l y be t h e c a s e . S c a t t e r i n g c u r v e s have been o b t a i n e d f o r samples c o n t a i n i n g d i f f e r e n t water amounts and a d i f f e r e n t H 0 / D 0 r a t i o . F o r example, f o r a specimen soaked i n a m i x t u r e o f 12.5% H 0/87.5% D 0 ( t o t a l water c o n t e n t i s 16% by w e i g h t ) e s s e n t i a l l y no s c a t t e r i n g was o b s e r v e d above a c o n s t a n t background. This r e s u l t i n i t s e l f indicates that t h e s c a t t e r i n g system c o n t a i n s e s s e n t i a l l y two phases o r c o n t r a s t regions. The m a t c h i n g c o n c e n t r a t i o n , known as t h e i s o p i c n i c p o i n t , corresponds to the c o n c e n t r a t i o n at which 2

2

2

3i = ( p 2 / p i ) 3

2

2

S i n c e each v a l u e o f β changes l i n e a r l y w i t h t h e r a t i o [ D O ] / [ H O ] t h e d e n s i t y v a l u e s change l i t t l e , [ i / l f l ( J s h o u l d be l i n e a r as 2

and


2


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COULOMBIC INTERACTIONS IN MACROMOLECULAR SYSTEMS

Figure 3. C o n c e n t r a t i o n p r o f i l e s f o r d i f f e r e n t membranes g i v i n g an element c o n c e n t r a t i o n ( i n a r b i t r a r y u n i t s ) a c r o s s t h e t h i c k n e s s a and b, Cu c o n c e n t r a t i o n a f t e r exchange. The membranes have been o b t a i n e d from a low d e n s i t y p o l y e t h y l e n e a f t e r i r r a d i a t i o n g r a f t i n g w i t h s t y r e n e f o l l o w e d by s u l f o n a t i o n . c, Cu c o n c e n t r a t i o n a f t e r exchange. The membrane has been o b t a i n e d from a copolymer o f t e t r a f l u o r o r e t h y l e n e and f l u o r i n a t e d p r o p y l e n e a f t e r i r r a d i a t i o n g r a f t i n g w i t h s t y r e n e f o l l o w e d by s u l f o n a t i o n . d, CI c o n c e n t r a t i o n a f t e r c h l o r h y d r a t a t i o n o f d i m e t h y l annio e t h y l m e t h a c r y l a t e g r a f t e d on polyvinylidene fluoride.

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f

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Figure 4. C h a r a c t e r i s t i c curve o b t a i n e d i n a s m a l l a n g l e s c a t t e r i n g experiment showing b o t h t h e peak and t h e z e r o o r d e r s c a t t e r i n g increase.


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a f u n c t i o n of [ D 2 0 ] / [ H 2 0 ] . Such a dependence i | shown i n F i g u r e 5 i n w h i c h the c o n s t a n t of m u l t i p l i c a t i o n L / H o] experimentally o b t a i n e d t o g i v e the b e s t p o s s i b l e o v e r a l l s u p e r p o s i t i o n i s p l o t t e d v e r s u s [ D 0 ] / [ H 2 0 ] f o r d i f f e r e n t water c o n t e n t s . A good l i n e a r dependence i s o b s e r v e d f o r t h e h i g h w a t e r c o n t e n t samples. F o r low water c o n t e n t s t h e two phase a p p r o x i m a t i o n i s l e s s v a l i d . SAXS r e s u l t s c o n f i r m such a r e s u l t w i t h a p o s i t i v e d e v i a t i o n from Porod's law c h a r a c t e r i s t i c of d e n s i t y f l u c t u a t i o n s w i t h i n p h a s e s . These SANS r e s u l t s t h e r e f o r e c o n f i r m t h e e x i s t e n c e o f a s e p a r a t e d phase c o n t a i n i n g most o f the i o n i c exchange s i t e s and the h y d r a t i o n water. L o c a l c o n c e n t r a t i o n o f c a t i o n and c h e m i c a l c o m p o s i t i o n o f t h i s i o n i c phase i n d i f f e r e n t i o n exchange ionomer membranes has been o b t a i n e d from e l e c t r o n s p i n r e s o n a n c e (ESR) measurements o f C u exchanged c a t i o n i c membranes ( 4 ) . SANS e x p e r i m e n t s have shown t h a t no d r a s t i c change o c c u r s i n the m i c r o s t r u c t u r e o f t h e s e membranes upon neutralization. G e n e r a l i n f o r m a t i o n about t h i s m i c r o s t r u c t u r e can t h e r e f o r e be o b t a i n e d t h r o u g h use o f c a t i o n i c p r o b e s . A different s i t u a t i o n e x i s t s i n o t h e r i o n c o n t a i n i n g polymers where a complete r e o r g a n i z a t i o n o f the m i c r o s t r u c t u r e o c c u r s upon n e u t r a l i z a t i o n o f t h e a c i d i c groups. I

I

2

2


+ +

+ +

Local C u c o n c e n t r a t i o n s i n t h e membranes have been o b t a i n e d by comparing t h e c o r r e s p o n d i n g ESR s p e c t r a w i t h the s p e c t r a o b t a i n e d with reference C u s o l u t i o n s . Frozen r e f e r e n c e s o l u t i o n s (at l i q u i d n i t r o g e n t e m p e r a t u r e ) p e r m i t us t o get r i d o f t h e m o l e c u l a r m o t i o n s . P r i o r t o t h e experiment t h e samples have t h e r e f o r e been quenched from room t e m p e r a t u r e down t o 7 7 Κ i n t h e f i n g e r dewar o f the ESR spectrometer. The r e f e r e n c e s o l u t i o n s a r e aqueous s o l u t i o n s t o w h i c h we have added a c r y o p r o t e c t o r . I t has been shown t h a t such an a d d i t i o n p r e v e n t s c r y s t a l l i z a t i o n o f w a t e r d u r i n g c o o l i n g , thus p r e s e r v i n g the t o t a l C u concentrations. The C u c o n c e n t r a t i o n s range o f t h e r e f e r e n c e s o l u t i o n s ( 0 . 0 2 - 0 . 2 g C u / c m ) has been chosen i n o r d e r t o match t h e p o s s i b l e c o n c e n t r a t i o n s f o u n d i n the membranes. I t t u r n s out t h a t i n t h i s c o n c e n t r a t i o n range t h e r e a r e d r a m a t i c changes i n t h e shape o f the ESR s p e c t r a , t h e s e changes a r e due t o r e l a t i v e l y i m p o r t a n t changes i n the d i p o l e - d i p o l e and exchange i n t e r a c t i o n s between the e l e c t r o n i c s p i n s . F o r low c o n c e n t r a t i o n s , the spectrum i s v e r y s i m i l a r t o t h a t o f i s o l a t e d C u i o n s where t h e f o u r l i n e s due t o h y p e r f i n e i n t e r a c t i o n s w i t h t h e C u nuclear spins a r e c l e a r l y seen. F o r h i g h e r c o n c e n t r a t i o n s o n l y a b r o a d l i n e i s seen. A c o n t i n u o u s change i n the s p e c t r a i s o b s e r v e d when the con c e n t r a t i o n i s v a r i e d ( F i g u r e 6 ) . A few e m p i r i c a l p a r a m e t e r s , such as the w i d t h s a t h a l f and q u a r t e r o f maximum and r e l a t i v e h e i g h t s o f v a r i o u s components, have been used t o c h a r a c t e r i z e t h e s p e c t r a ; the changes i n t h e s e parameters v s . C u c o n c e n t r a t i o n s have been p l o t t e d i n F i g u r e 7. The v a r i o u s r e f e r e n c e s o l u t i o n s o b t a i n e d by c h a n g i n g b o t h the n a t u r e o f t h e s a l t ( s u l f a t e , n i t r a t e , and bromure) and t h e c r y o p r o t e c t o r ( d i m e t h y l s u l f o x i d e , g l y c e r o l , e t h y l e n e g l y c o l ) have g i v e n e s s e n t i a l l y the same r e s u l t s f o r the same C u concentrations. The changes o b s e r v e d from one spectrum to a n o t h e r a r e s m a l l compared t o t h e changes o b s e r v e d w i t h a s m a l l m o d i f i c a t i o n o f the C u concentra tion. We can t h e r e f o r e assume, i n f i r s t a p p r o x i m a t i o n , t h a t an ESR spectrum i s c h a r a c t e r i s t i c o f t h e C u concentration. Because t h e + +

+ +

+ +

+ +

3

+ +

+ +

+ +

+ +

+ +

+ +


166


0 5

i


-S—s-

-05

J

-1

-τ*·

0 25

. 05

I.D.O'l

075

1

Figure 5. M u l t i p l i c a t i o n used i n superposition of Figures 2-4 a function of [ H O ] / [ D O ] . 2

as

2

1000 Gouts

Figure 6. ESR spectra of reference solutions at 77 Κ with d i f f e r e n t Cu concentration (g Cu /cm ): a, 0.19; b, 0.105; c, 0.042; and d e f i n i t i o n of the d i f f e r e n t parameters used to characterize the spectra. Reproduced with permission from Ref. 4. Copyright 1983 J. Appl. Polym. S c i . + +

++

3



13.

PINERI


Gauss

167

k

300-

200-

100 50οί ο.01

0.1

++/ 3 n g Cu /cm

Figure 7. Changes i n t h e w i d t h s p e c t r a l parameters v s . C u concen t r a t i o n of the reference s o l u t i o n s . Key: Χ, δχ; ο, ό ; • , 6 3 ; ·, Δ , Ηρρ. Reproduced w i t h p e r m i s s i o n from Ref. 4. C o p y r i g h t 1983. J . A p p l . Polym. S c i . + +

2


168


d i p o l e - d i p o l e and exchange i n t e r a c t i o n s a r e s h o r t range, the measured c o n c e n t r a t i o n s a r e l o c a l c o n c e n t r a t i o n s on a few t e n s o f A s c a l e . Use o f c r y o p r o t e c t o r s p e r m i t s us t o have homogeneous s o l u t i o n s so t h a t the l o c a l and average c o n c e n t r a t i o n s a r e t h e same i n t h e r e f e r e n c e solutions. However, i n t h e membranes where we expect i o n i c s e g r e g a t i o n s , t h e l o c a l c o n c e n t r a t i o n s measured by ESR s h o u l d be d i f f e r e n t from t h e average c o n c e n t r a t i o n d e f i n e d from c h e m i c a l a n a l y s i s . I n T a b l e I a r e summarized t h e r e s u l t s o b t a i n e d f o r d i f f e r e n t sample: N a f i o n p e r f l u o r o e t h y l e n e membrane (NAF), a c r y l i c a c i d i r r a d i a t i o n g r a f t e d p o l y t e t r a f l u o r o e t h y l e n e (PTFE), s u l f o n a t e d s t y r e n e i r r a d i a t i o n g r a f t e d f l u o r i n a t e d e t h y l e n e p r o p y l e n e copolymer (RAI), and s u l f o n a t e d p o l y s u l f o n e (SPS).


+ +

T a b l e I . Average and l o c a l C u c o n c e n t r a t i o n s i n membranes c o r r e s ponding t o d i f f e r e n t degrees o f exchange and d i f f e r e n t water c o n t e n t s

Exchange capacity meq/g

Specimen

Average concentration

Μ,

Water content

++

Local [Cu ] (g/cm ) 3

g/g

Concentration ratio

g/cm 0.8 0.8 0.8 3.33 3.33 3.2 3.2 1.2 1.2 1.2 1.2 1.2 1.2 1.0 1.0 0.75 0.75 0.99 0.99

NAF NAF NAF PTFE PTFE PTFE PTFE RAI RAI RAI RAI RAI RAI SPS SPS SPS SPS SPS SPS

0.045 0.15 0.03 0.061 0.095 0.047 0.148 0.03 0.03 0.03 0.15 0.15 0.15 0.015 0.23 0.03 0.03 0.04 0.04

0.047 0.039 0.018 0.049 0.016 0.055 0.01 0.0524 0.0518 0.0652 0.0422 0.0417 0.0525 0.027 0.022 0.0063 0.0125 0.0227 0.0272

0.21 0.115 0.082 0.088 0.065 0.045 0.048 0.208 0.21 0.21 0.094 0.0987 0.105 0.096 0.077 0.042 0.046 0.0924 0.113

4.46 2.96 4.53 1.8 4.06 2.65 5.03 3.97 4.05 3.22 2.84 2.36 2 3.55 3.5 6.6 3.68 4.07 4.15

L e t us d i s c u s s some o f t h e r e s u l t s . The l o c a l c o n c e n t r a t i o n s a r e always l a r g e r than t h e average c o n c e n t r a t i o n o b t a i n e d from chemi c a l a n a l y s i s . T h i s i s d i r e c t e v i d e n c e f o r nonrandom d i s t r i b u t i o n o f i o n s i n t h e membranes. F o r i n s t a n c e , i n t h e low w a t e r c o n t e n t N a f i o n sample we found a r a t i o l a r g e r t h a n 4, which means t h a t t h e i o n i c phase r e p r e s e n t s l e s s than 25% o f t h e polymer. Such a l a r g e i o n i c c o n c e n t r a t i o n cannot be e x p l a i n e d o n l y by a phase s e g r e g a t i o n o f t h e e t h e r comonomer, w h i c h would g i v e a f a c t o r s m a l l e r t h a n 2, Therefore, the i o n i c phase has t o c o n t a i n Cu** i o n s , w a t e r , and o n l y p a r t o f t h e side chain. Another i n t e r e s t i n g p o i n t i s t h e change i n l o c a l concen t r a t i o n when t h e w a t e r c o n t e n t i s changed. I f the l o c a l C u concen t r a t i o n i n the sample c o n t a i n i n g 4.5% w a t e r by weight i s 0.21 g/cm , we can c a l c u l a t e t h e new C u c o n c e n t r a t i o n i f we assume t h a t when the water c o n t e n t changes from 4.5% t o 15% a l l the new absorbed water + +

3

+ +


13.

PINERI

169


+ +

m o l e c u l e s are absorbed i n the phase c o n t a i n i n g C u i o n s . W i t h such an h y p o t h e s i s we would expect to o b s e r v e a change i n the l o c a l con c e n t r a t i o n from 0.21 g/cnr to 0.107 g/cm . T h i s number i s p r e t t y c l o s e t o the e x p e r i m e n t a l v a l u e o f 0.115 g/cm and i s c o n s i s t e n t w i t h the h y p o t h e s i s t h a t most o f the water m o l e c u l e s a r e absorbed i n the i o n i c phase. We a l s o have to compare the l o c a l C u c o n c e n t r a t i o n w i t h the c o n c e n t r a t i o n o b t a i n e d by assuming t h a t we have a i o n i c phase c o n t a i n i n g o n l y w a t e r and C u i o n s i n t h i s h y d r a t e d sample. The 15% water c o n t e n t sample c o n t a i n s 20.5 water p e r C u and the c o r r e s p o n d i n g s o l u t i o n would t h e r e f o r e have a c o n c e n t r a t i o n o f 63(63 + 20.5 χ 18) = 0.145 g C u / g . The c o n c e n t r a t i o n i n g/cm w i l l be l a r g e r because the d e n s i t y i s g r e a t e r than 1, T h i s v a l u e i s d e f i n i t e l y l a r g e r t h a n the l o c a l c o n c e n t r a t i o n found i n t h i s sample (0,115 g / c m ) . The a b s o l u t e v a l u e s o f the l o c a l c o n c e n t r a t i o n a r e g i v e n w i t h i n 20% a c c u r a c y . The r e l a t i v e v a l u e s c o r r e s p o n d i n g t o changes i n water c o n t e n t s a r e o b t a i n e d w i t h an a c c u r a c y b e t t e r than 5%. A l l t h i s e v i d e n c e i n d i c a t e s a phase s e g r e g a t i o n o f the C u ions i n t h i s membrane. The l o c a l C u c o n c e n t r a t i o n i s t h r e e times l a r g e r than the average c o n c e n t r a t i o n i n the f u l l y h y d r a t e d specimen, and t h i s r a t i o i s s t i l l l a r g e r (^ 4.5) f o r the low water c o n t e n t s p e c i mens. The changes observed i n the l o c a l c o n c e n t r a t i o n s when the water c o n t e n t i s changed a r e c o n s i s t e n t w i t h the h y p o t h e s i s t h a t most o f the water m o l e c u l e s a r e g o i n g i n s i d e t h i s i o n i c phase. S i n c e the local C u c o n c e n t r a t i o n has been shown t o be s m a l l e r t h a n the C u c o n c e n t r a t i o n o b t a i n e d from a i o n i c phase c o n t a i n i n g o n l y w a t e r and Cu i o n s , some o t h e r o r g a n i c groups have to be i n c l u d e d i n t h i s phase. S i m i l a r r a t i o s o f the l o c a l i o n c o n c e n t r a t i o n v e r s u s the a v e r a g e c o n c e n t r a t i o n have been o b t a i n e d f o r the o t h e r membranes. F o r some membranes the d e f i n i t i o n of the l o c a l c o n c e n t r a t i o n i s more d i f f i c u l t , p r o b a b l y because of s u p e r p o s i t i o n o f d i f f e r e n t i o n i c s p e c i e s . These e l e c t r o n s p i n resonance s t u d i e s d i r e c t l y show the e x i s t e n c e o f phase s e g r e g a t i o n i n t h e s e i o n exchange membranes. The i o n i c phase i s made o f the i o n s , water m o l e c u l e s , and p a r t o f the side chains. Mossbauer s p e c t r o s c o p y i s a p o w e r f u l t e c h n i q u e t o g i v e i n f o r m a t i o n on the i o n i c phase a f t e r exchange w i t h s p e c i f i c c a t i o n s l i k e Fe, E u or Sn. Most o f our work on the p e r f l u o r i n a t e d ionomer membranes has been done w i t h F e and F e ions (5,6). A typical r e s o n a n t a b s o r p t i o n experiment uses a monochromatic r a d i o a c t i v e Mossbauer s o u r c e w h i c h emits γ r a y s ; the sample to be s t u d i e d i s used as an a b s o r b e r and must c o n t a i n n u c l e i o f the same s t a b l e i s o t o p e e m i t t e d by the s o u r c e . Resonant a b s o r p t i o n o c c u r s whenever the d i f f e r e n c e i n energy between the ground and e x c i t e d s t a t e s o f the n u c l e i i n s o u r c e and a b s o r b e r p r e c i s e l y c o i n c i d e . Each s t a t e i s s p l i t by h y p e r f i n e i n t e r a c t i o n o f the n u c l e a r e l e c t r i c and m a g n e t i c moments w i t h the e l e c t r i c and m a g n e t i c f i e l d s c r e a t e d at the n u c l e u s by i t s s u r r o u n d i n g e l e c t r o n s and more d i s t a n t atoms. The energy o f γ r a y s e m i t t e d by the s o u r c e i s s l i g h t l y modulated; the spectrum i s scanned by v a r y i n g the D o p p l e r s h i f t o b t a i n e d by moving the s o u r c e w i t h a v e l o c i t y , v , 10 mm/s. D i f f e r e n t i n f o r m a t i o n can be e x t r a c t e d from the a b s o r p t i o n spectra. The a r e a o f the a b s o r p t i o n spectrum i s governed by the p r o b a b i l i t y o f a n u c l e u s a b s o r b i n g a γ photon e m i t t e d by the s o u r c e 3

3

+ +

+ +

+ +

+ +

3


3

+ +

+ +

+ +

+ +

+ +

5 7

1 5 1

1 1 3

+ +

+ + +


170


without r e c o i l . 2

The r e c o i l e s s 2

2

-E /h c f = e

fraction i s :

2

Ύ

2

where i s the mean square d i s p l a c e m e n t o f the a b s o r b i n g n u c l e u s . A b s o r p t i o n d i s a p p e a r s e n t i r e l y when d i v e r g e s a t the m e l t i n g p o i n t o r n e a r the g l a s s t r a n s i t i o n o f a n o n c r y s t a l l i n e phase. The q u a d r u p o l e s p l i t t i n g v a l u e s r e f l e c t the e x i s t e n c e o f an e l e c t r i c f i e l d g r a d i e n t produced by the asymmetry i n the e l e c t r o n s o r n e i g h b o u r i n g atoms d i s t r i b u t i o n . S t r u c t u r a l i n f o r m a t i o n can a l s o be d e r i v e d from the e f f e c t s o f m a g n e t i c i n t e r a c t i o n s on F e spectra. A p a r a m a g n e t i c h y p e r f i n e s t r u c t u r e can be o b s e r v e d when the d i s t a n c e s between F e i o n s a r e l a r g e enough t o g i v e l o n g e l e c t r o n i c r e l a x a t i o n t i m e s . Small i r o n r i c h c l u s t e r s may o r d e r m a g n e t i c a l l y and l e a d to superparamagnetism above a c e r t a i n b l o c k i n g temperature. Mossbauer s p e c t r o s c o p y r e s u l t s w i t h F e and F e perfluorina ted ionomer membranes can be summarized. F i r s t o f a l l , Mossbauer a b s o r p t i o n d i s a p p e a r s at temperatures u s u a l l y w e l l below 0°C. Such a r e s u l t a l r e a d y e x c l u d e s the e x i s t e n c e o f i r o n i o n s d i s p e r s e d i n a p e r f l u o r i n a t e d m a t r i x f o r which we would o b s e r v e a d i s a p p e a r a n c e o f a b s o r p t i o n a t a temperature c o r r e s p o n d i n g t o the g l a s s t r a n s i t i o n o f the m a t r i x 3 0 0 ° C ) . I n F i g u r e 8 a r e p l o t t e d the changes i n £nf v e r s u s temperature f o r d i f f e r e n t water c o n t e n t s . A d e v i a t i o n from the s t r a i g h t l i n e c o r r e s p o n d i n g t o a Debye model w i t h θ = 140 Κ appears a t a temperature a s s o c i a t e d w i t h a g l a s s t r a n s i t i o n o f t h e i o n i c phase c o n t a i n i n g water and i o n s . Such a r e s u l t i s c o n s i s t e n t w i t h the NMR r e s u l t s and q u a s i e l a s t i c n e u t r o n s c a t t e r i n g from which water p r o t o n s have been found to be m o b i l e down to temperatures of the o r d e r o f 200 K. 2

+ 3


+ + +

+ +

+ + +

In F i g u r e 9 a r e shown the low temperature p a r a m e t e r s o f a f e r r o u s N a f i o n as a f u n c t i o n o f water c o n t e n t . A d r a s t i c change o c c u r s between 0 and 8% w e i g h t water c o n t e n t f o r a l l the p a r a m e t e r s . This r e s u l t , associated with Na , H NMR r e s u l t s and w i t h heat o f s o r p t i o n changes, i m p l i e s t h a t the f i r s t water m o l e c u l e s a r e absorbed s p e c i f i c a l l y a t the c a t i o n s . Through a n a l y s i s o f the m i c r o s t r u c t u r e o f the i o n i c phase i n the Fe exchanged membranes d i f f e r e n t i o n i c s p e c i e s have been i d e n tified: • isolated F e i o n s g i v i n g a p a r a m a g n e t i c h y p e r f i n e spectrum; • dimers g i v i n g a s p e c i f i c d o u b l e t w i t h a l a r g e q u a d r u p o l e s p l i t t i n g ; • i r o n i n groups c o n t a i n i n g even numbers o f a n t i f e r r o m a g n e t i c a l l y coupled f e r r i c ions. E v i d e n c e o f the e x i s t e n c e o f a s e p a r a t e i o n i c h y d r o p h i l i c phase has t h e r e f o r e been o b t a i n e d from t h e s e d i f f e r e n t measurements. The l o c a l s t r u c t u r e i n s i d e t h i s i o n i c phase seems to depend s t r o n g l y on the n a t u r e o f t h e c a t i o n . S p e c i f i c a s s o c i a t i o n s have been found f o r Fe ions. The q u e s t i o n which a r i s e s now c o n c e r n s t h e geometry o f these i o n i c a s s o c i a t i o n s . T h i s problem w i l l be d e v e l o p e d i n the next chapter. +

+

+ + +

+ 3

+ + +

Dimensions

o f t h e I o n i c Domains

A t y p i c a l b e h a v i o r o b s e r v e d i n ionomers i s the e x i s t e n c e of a s m a l l a n g l e s c a t t e r i n g peak (from X r a y o r n e u t r o n e x p e r i m e n t s ) and a z e r o



13.

PINERI


o

5

δ

Si

Έο

171

2io τ

κ

Figure 8. tnî v s . Τ f o r a f e r r o u s N a f i o n as a f u n c t i o n o f water content. Key: • , 3.6% H 0; ·, 6.6% H 0 ; • , 7.8% H 0; o, 17.5% H 0 . The s o l i d l i n e c o r r e s p o n d s t o t h e t h e o r e t i c a l tnf c u r v e w i t h 0pj = 140 K. I n s e r t shows t h e temperature, To, a t w h i c h the f - f a c t o r f a l l s to zero. 2

2

2

2

20 HtOwtJghtVt Figure 9. Low temperature (4.2 K) parameters o f a f e r r o u s N a f i o n as a f u n c t i o n o f w a t e r c o n t e n t ( o n e - s i t e f i t ) . Reproduced w i t h p e r m i s s i o n from Ref. 9. C o p y r i g h t 1984 J . R e a c t i v e Polym.




172

o r d e r s c a t t e r i n g i n c r e a s e . Both t h e i n t e n s i t y and t h e p o s i t i o n o f t h e peak change w i t h water c o n t e n t . T h i s peak has t h e r e f o r e been a s s o c i a t e d w i t h t h e i o n i c h y d r o p h i l i c domains. A n a l y s i s o f t h i s peak i n terms o f a Bragg peak r e s u l t i n g o f t h e p r e s e n c e o f a p o l y c r y s t a l l i n e l a t t i c e o f s p h e r i c a l i o n i c a g g r e g a t e s has been made by T. G i e r k e (7) f o r t h e N a f i o n p e r f l u o r i n a t e d m a t e r i a l s . The proposed model a l s o based on i o n t r a n s p o r t i m p l i e s t h e e x i s t e n c e o f t h e s e s p h e r i c a l i o n i c c l u s t e r s s e p a r a t e d by s m a l l c h a n n e l s w h i c h p e r m i t t h e i o n and water diffusion. I n a s i m i l a r system, F u j i m u r a (J_) c o n c l u d e d t h a t t h e gen e r a l a s p e c t s o f the v a r i a t i o n o f t h e s c a t t e r i n g p r o f i l e s w i t h s w e l l i n g and d e f o r m a t i o n can be q u a l i t a t i v e l y d e s c r i b e d by one o f the f o l l o wing models: ( i ) a two phase model i n which s p h e r i c a l i o n i c aggregates a r e d i s p e r s e d i n t h e p o l y m e r i c m a t r i x o r ( i i ) t h e c o r e s h e l l model. In a another study ( 8 ) , we have a n a l y z e d the l i t e r a t u r e d a t a a s s o c i a t e d w i t h our SANS d a t a and shown t h a t t h e s c a t t e r i n g d a t a on p e r f l u o r o s u l f o n a t e d ionomer membranes a r e c o n s i s t e n t w i t h t h e s c a t t e r i n g produced by a group o f h a r d spheres d i s p e r s e d i n t h e p o l y m e r i c matrix. The number o f i o n s p e r c l u s t e r was found t o change w i t h t h e water a b s o r p t i o n v a l u e s , w i t h the c a t i o n , and w i t h e q u i v a l e n t w e i g h t . The o c c u r e n c e o f t h e s c a t t e r i n g maxima i s due t o i n t e r f e r e n c e e f f e c t s between c l u s t e r s . F u r t h e r c a l c u l a t i o n s have t o be made t o t a k e i n t o account a p o s s i b l e a n i s o t r o p y o f t h e s e i o n i c s p h e r e s . Attempts t o L a b e l t h e I o n i c Domains We have completed experiments l a b e l the i o n i c domains. We have found e v i d e n c e o f a p r e c i p i t a t i o n phenomenon o f p a r t i c l e s o f i r o n o x i d e o r h y d r o x i d e when an i r o n form o f membrane was exchanged by d i f f e r e n t o t h e r i o n s l i k e K , N a , e t c . We t h e r e f o r e have a n a l y z e d t h e s e p a r t i c l e s by d i f f e r e n t t e c h n i q u e s - l i k e X r a y s , Mossbauer s p e c t r o s c o p y , m a g n e t i c measurements and e l e c t r o n m i c r o s c o p y - w i t h two g o a l s i n mind. F i r s t o f a l l the f o r m a t i o n o f u l t r a t h i n p a r t i c l e s i s v e r y i m p o r t a n t i n d i f f e r e n t domains and e s p e c i a l l y i n c a t a l y s i s when t h e s e membranes a r e used i n t h e s o l i d polymer e l e c t r o l y t e process. Second, we e x p e c t some c o r r e l a t i o n between t h e s i z e s and d i s t r i b u t i o n o f p r e c i p i t a t e s w i t h the s t a r t i n g i o n i c domains. +

+

Let us summarize here some p r e v i o u s r e s u l t s (9,10). When soaking a F e membrane l i k e N a f i o n 1200 i n a s o l u t i o n o f K , t h e exchange i s e f f e c t e d b u t the i r o n i s n o t e l i m i n a t e d from t h e membrane. We i n d e e d have a Mossbauer a b s o r p t i o n b u t a v e r y d i f f e r e n t spectrum ( F i g u r e 10), A l l o f the i r o n i s now c o n t a i n e d i n a s i n g l e new phase which d i s p l a y s a m a g n e t i c a l l y s p l i t h y p e r f i n e p a t t e r n a t 4.2 K. The s t r u c t u r e o f t h i s new phase depends on d i f f e r e n t paramet e r s , t h e most i m p o r t a n t o f which seems t o be the i n i t i a l water content. Amorphous f e r r i c h y d r o x i d e has been o b t a i n e d f o r low water contents. aFeOOH ( g o e t h i t e ) i s o b t a i n e d f o r h i g h water c o n t e n t (118%). aFe 0 (hematite) i s o b t a i n e d when a sample f i r s t exchanged with F e i s a u t o c l a v e d a t 150°C. + 3

2

+

3

+ 3

The d i s t r i b u t i o n o f these p r e c i p i t a t e s a c r o s s t h e membrane t h i c k n e s s i s n o t u n i f o r m , as has been shown by e l e c t r o n m i c r o p r o b e F i g u r e 1 1 ) . The p r o f i l e form depends on d i f f e r e n t p a r a m e t e r s such as time o f s o a k i n g i n KOH s o l u t i o n s , KOH c o n c e n t r a t i o n s , e t c . These p a r t i c l e s o f aFeOOH and a F e 0 have been o b s e r v e d d i r e c t l y 2

3



13.

PINERI


173

+ 3

F i g u r e 10. Mossbauer s p e c t r a a t 4.2 Κ o f an F e . N a f i o n sample b e f o r e (a) and a f t e r (b) reexchange w i t h K . Reproduced w i t h p e r m i s s i o n from Ref. 9. C o p y r i g h t 1984 J . R e a c t i v e Polym. +

Figure before

11. D i s t r i b u t i o n o f i r o n a c r o s s t h e t h i c k n e s s o f t h e membrane (a) and a f t e r (b) exchange w i t h K . +


174


i n u l t r a t h i n ( 5 0 0 Â ) s e c t i o n s o f t h e s e p e r f l u o r o s u l f o n a t e membranes by t r a n s m i s s i o n e l e c t r o n m i c r o s c o p y (TEM) . aFe203 p a r t i c l e s (y 1 0 0 A i n d i a m e t e r ) a r e r o u g h l y s p h e r i c a l ; they a r e grouped t o g e t h e r i n c l u s t e r s r a n g i n g from a few hundred up t o about 1 0 0 0 Â . These c l u s t e r s a r e u n i f o r m l y d i s t r i b u t e d a c r o s s t h e membrane t h i c k ness. The aFeOOH p a r t i c l e s a r e i n t h e form o f w e l l s e p a r a t e d a c i r c u l a r o r b l a d e shaped c r y s t a l l i t e s up t o 1 0 0 0 Â l o n g and about 1 0 0 Â across. These r e s u l t s may c o n s t i t u t e a f i r s t v a t i o n o f i o n i c domains.

s t e p toward a d i r e c t

obser-


Conclusions Many o r g a n i c p o l y m e r i c i o n exchange membranes have a t h r e e phase structure: • microcrystallites; • i n t e r m e d i a t e h y d r o p h o b i c phase; • h y d r o p h i l i c i o n i c domains t h a t c o n s t i t u t e t h e a c t i v e p a r t o f t h e membrane f o r t h e i o n exchange p r o c e s s . We have g i v e n many e x p e r i m e n t a l r e s u l t s c o n c e r n i n g t h i s i o n i c phase i n terms o f c h e m i c a l c o m p o s i t i o n , dynamic p r o p e r t i e s , m i c r o s t r u c t u r e o f t h e i o n i c complexes and geometry o f t h e domains. Acknowledgment s The work d e s c r i b e d i n t h i s a r t i c l e summarizes g e n e r a l r e s u l t s o b t a i ned by d i f f e r e n t coworkers i n c l u d i n g D r s . J.M.D. Coey, B. Rodmacq, A. Meagher f o r Mossbauer s p e c t r o s c o p y ; D r s . E . Roche, R. D u p l e s s i x and S. Kumar f o r SANS e x p e r i m e n t s ; D r s . F. V o l i n o and D. G a l l a n d f o r ESR; D r s . J . K e l l y , A. M i c h a s , J . C I . J e s i o r f o r p r e c i p i t a t i o n s t u d i e s , D r s . B. D r e y f u s and M. Escoubes f o r g e n e r a l d i s c u s s i o n s on thermodynamic r e s u l t s .

Literature Cited 1. 2. 3. 4.

"Perfluorinated Ionomer Membranes," Eisenberg, Α.; Yeager, H.L., Editors, ACS Symposium Series 180, 1982. Roche, E.; Pinéri, M.; Duplessix, R.; Levelut, A.M. J. Polym. Sci. Polym. Physics 1981, 19, 1-11. Roche, E.; Pinéri, M.; Duplessix, R. J. Polym. Sci. Polym. Physics 1982, 20, 481. Vasquez, B.; Avalos, J.; Volino, F.; Pinéri, M. J. Appl. Polym. Sci.

5. 6.

1983,

28,

1093-1103.

Rodmacq, B.; Coey, J.M.D.; Pinéri, M. Revue de Physique Appliquée 1980, 15, 1179-1182. Rodmacq, B.; Pinéri, M.; Coey, J.M.D.; Meagher, A. J . Polym. Sci., Polym. Physics 1982, 20, 602-621.

7.

Gierke, T.D.; Hsu, W.Y.

8. 9.

Kumar, S.; Pinéri, M., submitted to Journal of Polymer Science. Meagher, Α.; Rodmacq, Β.; Coey, J.M.D.; Pinéri, M. J . Reactive

Ref.

1, 283-310.

10.

Pinéri, M.; Coey, J.M.D.; Jesior, J . C l . , submitted to Journal of Reactive Polymers.

Polym. 1984, 2, 51-59.

RECEIVED November 27, 1985


Coulombic Interactions in Macromolecular Systems - American

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