Converse piezoelectric behavior of three-dimensionally printed polymer and comparison of the in-plane and out-of-plane behavior

The converse piezoelectric effect (out-of-plane and in-plane directions) is reported in 3D-printed polymer without filler or poling, consistent with previously reported direct piezoelectric effect (out-of-plane direction only). Resin 1 (acrylate ester, viscosity 95 cP) and Resin 2 (methacrylate, viscosity 2950 cP) are used in the printing by stereolithography. Both direct and converse effects stem from the 2D shear stress during printing causing 2D in-plane molecular alignment. Due to its higher viscosity, Resin 2 gives more molecular alignment and hence higher piezoelectric coupling coefficient d (0.4 vs. 0.2 pC/N). The out-of-plane d is similar for the direct and converse effects in the linear regime, which occurs below 30 kPa compressive stress in the direct effect and below 1 V/m in the converse effect. Both converse and direct effects are reversible, whether in the linear regime or not. The higher is the applied electric field, the lower is d, due to strain saturation.