History and recent progress in piezoelectric polymer research

Electrets of carnauba wax and resin exhibited good stability of trapped charges for nearly 50 years. Dipolar orientation (heterocharge) and trapped charge (homocharge) are two mechanisms contributing the pyro-, piezo-, and ferroelectricity of polymers. Since 1950's shear piezoelectricity was investigated in polymers of biological origin, such as cellulose and collagen as well as synthetic optically active polymers, such as polyamides and polylactic acid Since the discovery of piezoelectricity in poled polyvinylidene fluoride (PVDF) in 1969, the pyro-, piezo-, and ferroelectricity went widely investigated in a number of polar polymers, such as copolymers of vinylidene fluoride and trifluoroethylene, a copolymer of vinylidenecyanide and vinylacetate, and nylons. Recent studies involve the electric activities of submicron films of aromatic and aliphatic polyureas, prepared by vapor deposition polymerization in vacuum and the piezoelectricity of polyurethane produced by the coupling of electrostriction and the bias electric field.