Piezoelectricity and pyroelectricity in polymers

Abstract

Piezoelectric properties of polymeric substances arise from either the poling-induced orientation of molecular dipoles (class 1) or the uniaxial orientation of chiral chain molecules (class 2). The class 1 polymers include ferroelectric polymers, polar polymers with frozen-in dipole orientation, and the composites of polymers with ferroelectric ceramics. Details of the poling procedure in representative materials are described, and optimum poling conditions are suggested. Resulting piezoelectric and pyroelectric activities are specified as a function of remnant polarization, and underlying basic mechanisms are summarized. The class 2 polymers consist of drawn optically active polymers and exhibit face-shear piezoelectricity appearing in proportion to the orientation coefficient of chain axes. The spontaneous polarization of ferroelectric liquid-crystalline polymers is attributable to this type of piezoelectricity coupled with the spontaneous strain.<>