Thermally stable cellular poly(vinylidene) ferroelectrets: Optimization of CO2 driven inflation process

Electrically charged cellular ferroelectrets can show excellent thermally stable piezoelectric activity and are therefore progressively used in electrochemical transducers. Given that an optimized cellular structure is a key for improving charge density and the associated piezoelectric properties in this material, we investigated the influence of CO2 inflation treatment using various gas diffusion expansion or inflation procedures on the piezoelectric d(33) coefficient and thermal stability of cellular poly(vinylidene) ferroelectrets and compare with the results (partially) obtained by N-2 inflation as reported in our previous study (Jahan, Mighri, Rodrigue, Ajji, J. Appl. Polym. Sci. 2019, 136, 47540). Samples were prepared using the conventional extrusion-stretching-inflation-corona charging method. Maximum d(33) coefficient for CO2-inflated samples is found to be around 30% higher than that of N-2-inflated samples (327 pC/N compared to 251 pC/N) by stepwise pressure application method. The key parameters addressed in the inflation procedures are the changes in sample thickness, morphology, and the void-height distribution in both gas treatments. The ferroelectrets show excellent thermal stability for up to 4 days at 90, 110, and 120 degrees C in both treatments with a slightly improved performance in CO2 gas. The higher activation energy of CO2-inflated samples (0.52 eV) than the N-2-inflated ones (0.43 eV) further confirms the stability data. (c) 2019 Wiley Periodicals, Inc.