PIEZOELECTRIC RELAXATION IN POLY(GAMMA-BENZYL-GLUTAMATE)

Theoretical considerations are followed by a description of an experimental program in which the piezoelectric d- and e-constants, together with the elastic constant and the dielectric constant, were measured for oriented poly( gamma -benzyl-glutamate) (PBG) films with various elongation ratios as a function of frequency and temperature. The results are discussed in terms of a general theory of piezoelectricity for inhomogeneous systems, in particular for a disperse two-phase system. The piezoelectricity of PBG films is proved to originate from the piezoelectric and optically active symmetry of PBG crystallites and their orientation distribution. The piezoelectric relaxation of PBG due to thermal motion of the side chains has a dual character: it is relaxational at lower frequencies and retardational at higher frequencies. On the assumption that the alpha -helical main chains surrounded by the bulky side chains are responsible for the origin of the piezoelectricity, such relaxation phenomena are interpreted in terms of the relaxation of the local elastic field in the main chains. An equivalent model having the same frequency characteristics is proposed to include the higher order structure of the PBG film.