Freestanding 3D piezoelectric PVDF sensors via electroprinting

Abstract

Polyvinylidene fluoride, PVDF is a soft piezoelectric material with potential applications in robotic sensors and actuators, wearable electronics, and energy harvesting. The sensitivity of piezoelectric PVDF is attributed primarily to the β-crystalline phase with oriented dipoles. 3D electroprinting process is a promising technique to achieve 3D PVDF-based piezoelectric devices because the combined mechanical stretching and electric field-assisted poling can improve the electroactive crystalline phases in PVDF. In this work, we show that the incorporation of an anti-solvent in the PVDF solution was instrumental in obtaining an optimum solution viscosity and solvent evaporation rate to achieve mechanically stable layer-by-layer printing. Two major process parameters further influencing the resolution of the printed structure were nozzle-to-collector distance and extrusion pressure. Freestanding 3D PVDF structures with an average individual layer height as small as 30 µm and continuous prints for multiple 3D designs have been achieved. FTIR and XRD spectra show an improvement in the electroactive β and γ phases in the electroprinted PVDF compared to the dominant α phase of PVDF powder. Furthermore, the 3D PVDF structures display sensitivity to various load profiles at varying frequencies with the piezoelectric voltage coefficient (g33) range between 1.72E-4 and 4.08E-4 V.m/N.