Field-Induced Crystallization in Highly Plasticized Poly(vinylidene fluoride) Films.
RUTGERS - THE STATE UNIV PISCATAWAY NJ DEPT OF MECHANICS AND MATERIALS SCIENCE
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Highly plasticized films of polyvinylidene fluoride PCF2 containing approximately 18 by weight of tricresyl phosphate TCP and with initial crystallinites phase II of approximately 15 were poled under high vacuum. The poling temperatures were 75 C and 90 C and the poling field was 250 KVcm. The poling time was varied from 15 minutes to 240 minutes. Weight measurements and X-ray diffraction data of poled films showed that with increasing poling time, up to 4 hrs that plasticizer content decreased to a minimum of 11 and the crystallinity of the PVF2 films increased to a maximum of 45. The field induced crystallization occurred as highly oriented phase I crystals. After poling for 1 hour at 90 C, a significant percent of the crystalline material was observed to be in the polar phase I form. At longer times, a measure of the relative percent of phase I with respect to the total crystallinity decreased. As expected, the piezoelectric strain coefficient d sub 31, stress coefficient e sub 31, and pyroelectric coefficient P sub y increased with increasing phase I content, reaching maximum values after a 1 hour poling time at 90 C of d sub 31 approx. 10 PCN, e sub 31 approx. 11 mcm2 and P sub y approx. 17 micro Cm per deg K. The dynamic mechanical modulus and dielectric constant measured at 3 Hz were found to be approx. 1.3 GNsq m and approx. 14.7 respectively under these poling conditions.
- Electricity and Magnetism