HIGH-FIELD ELECTROSTRICTIVE RESPONSE OF POLYMERS

It is well known that electrostrictive strains are proportional to the square of the applied electric field. It therefore appeared reasonable to assume that for some polymeric materials, a large acoustic thickness response, d(T), (d(T) = dS/dE) might be obtained by application of high dc bias fields, similar to 20 MV/m, to a film while driving the film with an ac signal to access the high slope region of the electrostrictive strain vs. applied field curve. Previous studies of crystallizing poly(vinylidene fluoride) (PVF2) from solution under high electric fields have demonstrated that gel-like samples of PVF2 with high content of the plasticizer tricresyl phosphate (TCP) could be subjected to electric fields as high as similar to 100 MV/m. Using this type of heavily plasticized PVF2, d(T) values similar to 4 Angstrom/V were obtained. Values of 9 Angstrom/V were obtained for a certain class of thermoplastic elastomer (i.e., a polyurethane). These d(T) values are considerably greater than those obtained from conventional piezoelectric ceramic materials. In addition, large elastic strains (> 3%) were observed as a function of applied dc field. (C) 1994 John Wiley and Sons, Inc.