A Study of the Nature and Origin of Pyroelectricity and Piezoelectricity in Polyvinylidenefluoride and its Copolymer with Tetrafluoroethylene.
Abstract
X-ray diffraction profiles, piezoelectric strain coefficient d31 and the pyroelectric coefficient P3 of 50 microns (Form 2 crystallites only) and 25 microns (both Form 1 and Form 2 crystallites) thick PVF2 films have been studied after (i) corona poling (ii) uniaxial stretching and (iii) uniaxial stretching and corona poling. The results suggest that the induced piezo- and pyroelectricity in PVF2 is of dipolar origin. However, there is a difference in a sense that corona poling alone at fields 1/3 x 10 to the 8th power Vm produces mainly an intermediate polar form of Form 2 crystallites by a co-operative rotation of the alternate polymer chains through 180 degrees about the chain axis (i.e. c-axis) without losing its T-G-T-G' molecular conformation and the unit cell dimensions remaining unaltered. Uniaxial stretching, however, produces a direct conversion to the polar Form 1 type of structure from the non-polar Form 2 crystallites. A study of birefringence and small angle light scattering (SALS) patterns has also been made with uniaxially stretched PVF2 films, originally containing only Form 2 (non-polar) crystallites. The results indicate that the major contribution to the observed orientation, producing Form 1 type polar crystallites, originates from the crystallite regions of the polymer. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 01, 1978
- Accession Number
- ADA062759
Entities
People
- Dilip K. Das-Gupta
Organizations
- Bangor University