Compressometer based method for measuring converse electrostriction in polymers

Electrostriction is the fundamental mechanism of electromechanical coupling in all insulator materials. In this work, the electrostrictive coefficients of several polymers were measured by a converse method. A modified compressometer for resolving fractional changes in capacitance of the order of 10^-6 was used. A highly sensitivity capacitance bridge GenRad 1615 was coupled with a lock-in amplifier to detect attofarad (10^-18) level capacitance changes caused by cyclic uniaxial stresses on samples. Measurements were done at room temperature with an electrical frequency of 1 kHz and a mechanical frequency of 0.4 Hz. We found negative electrostriction coefficients for the polymers tested. The influences of crystallinity, glass reinforcement, and blending were observed to affect the electrostriction behavior due to the fact that electrostriction is mainly governed by the elastic properties in low-permittivity polymers. Using these recent data, along with widely accepted data on ferroelectric materials and soft polymers, the linear relationship between electrostriction coefficient (Q) and the ratio of elastic compliance and dielectric permittivity (s/ε₀ρ_r) was confirmed. This leads to an effective way to predict the electrostriction coefficient in dielectric materials