Possible evidence for a glass transition in trans-(CH)x

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Solid State Communications, Printed in Great Britain.

POSSIBLE

Vol.52,No.ll,

EVIDENCE

pp.899-900,

FOR A G L A S S

1984.

TRANSITION

0038-I098/84 $3.00 + .00 Pergamon Press Ltd.

IN T R A N S - ( C H ) X

M. O. S t e i n l t z a n d R. V a l l e e D e p a r t m e n t of P h y s i c s , St. F r a n c i s X a v i e r U n i v e r s i t y Anttgontsh, Nova Scotia, C a n a d a B2G 1C0 (Received

30 August 1984

by

M. F. Collins)

A dilatometric

investigation has been carried out in the t e m p e r a t u r e r e g i o n a r o u n d 150K w h e r e other w o r k e r s h a v e seen a n o m a l i e s in o t h e r p r o p e r t i e s . An a n o m a l y suggestive of a glass t r a n s i t i o n has been o b s e r v e d .

I Recent proton NMR studies on films of trans-polyacetylene, (CH) have shown an abrupt change i~ linewidth beginning at about 155K. We have undertaken a dilatometric study of such f i l m s k i n d l y provided to us by Prof. A. J. H e e g e r of the U n i v e r s i t y of California at S a n t a B a r b a r a . Although we use a capacitance-dilatometer which applies a very s m a l l f o r c e ( a b o u t 10 -~ N) to the s a m p l e , the i n v e s t i g a t i o n of s u c h thin films does involve particular problems in o b t a i n i n g a sufficient sample length and in o b t a i n i n g a s a m p l e of s u f f i c i e n t rigidity to withstand the force applied. The p r o b l e m s w e r e o v e r c o m e by r o l l i n g a Icm w i d e by 5 c m long s t r i p of film into a c y l i n d e r of d i a m e t e r 0.5 cm and inserting the cylinder into a cylindrical brass collar of the same d i a m e t e r and a b o u t 0.5 cm l e n g t h . The samples were shipped under vacuum and w e r e h a n d l e d for a b o u t o n e m i n u t e u n d e r dry n i t r o g e n d u r i n g i n s e r t i o n into the dilatometer. The experiment was conducted in an a t m o s p h e r e of nitrogen boiled off from the liquid nitrogen used as a c o o l a n t . The c a p a c i t a n c e was measured using a General-Radio 1615 capacitance bridge and a lock-in amplifier connected via the GPIB interface bus to a Commodore PET computer which controlled the experiment and collected and reduced the data. F i g u r e I s h o w s the m e a s u r e d l e n g t h changes relative to the beryllium-copper cell for two consecutive w a r m i n g r u n s at a rate of 0.66K/minute. These data clearly indicate a transformation occurring in the r e g i o n a r o u n d 150K. The data are

Natural Research

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140 150 160 170 Temperoture ( Keivins )

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F i g u r e 1. Thermal expansivity (dl/1) of trans-(CH) relative to the beryllium-coppe~ cell over the temperauure range 110K to 200K after subtraction of a constant slope of 3 . 7 x i 0 -/K. The c u r v e s s h o w n are from two s e q u e n t i a l warming runs to room temperature.

consistent with the occurrence of a glass transition in the p o r t i o n o f the s a m p l e t h a t is a m o r p h o u s . This portion varies and is typically 205. A dielectric dispersion study similar to that c a r r i e d out on 2 P O l y c a r b o n a t e by Matsuoka and Ishida would go far toward confirming these ideas. This interpretation is c o n s i s t e n t with the results of thermostimulated creep measurements reported recently by E l s a y e d et al 3. We are v e r y g r a t e f u l to Prof. W. K l e i n of B o s t o n U n i v e r s i t y and Dr. D. M o s e s of the U n i v e r s i t y of California at Santa Barbara for helpful discussions and s u g g e s t i o n s .

W o r k s u p p o r t e d in p a r t by the Sciences and Engineering C o u n c i l of C a n a d a .

899

900

POSSIBLE EVIDENCE FOR A GLASS TRANSITION IN TRANS-(CH)

x

Vol. 52, No. I I

References. I. S. Ikehata, M. Druy, T. Woerner, A. J. Heeger and A. G. MaeDtarmid, Solid State Communications, 39, 1239-1242 (1981). 2. S. M a t s u o k a and Y. Ishida, Journal of Polymer Science P a r t C, 1~4, 247.

3. T. Elsayed, J. Elhout, B. F r a n c o i s , C. M a t h i s , D. C h a t a i n and C. L a e a b a n n e , J o u n a l de P h y s i q u e , C o l l o q u e C3, s u p p l . , 44, C3-131 - C 3 - 1 3 4 (1983).