Nonlinear capacitance dilatometry for investigating elastic and electromechanical properties of ferroelectrets

Abstract

Nonlinearities in ferroelectret polymer foam capacitors arise from voltage-dependent thickness changes. Such thickness changes are caused by the converse piezoelectric and electrostrictive effects in these soft materials. The authors show that the higher harmonics of the current response during application of a sinusoidal voltage to ferroelectret capacitors provide information on the elastic and electromechanical properties of the foam. The authors demonstrate the potential of this versatile measurement technique by investigating the temperature dependence of the piezoelectric response and by monitoring the changes in the elastic and electromechanical properties during inflation of cellular polypropylene.

Influence of gas pressure in the voids during charging on the piezoelectricity of ferroelectrets

“…They are produced by stretching filler-loaded PP under suitable conditions. 25,26 Figure 1 shows the normalized capacitance decay in dry air at different pressures. In order to optimize their electromechanical properties, the samples were inflated by gas-diffusion expansion in nitrogen and subsequent heat treatment.…”