Direct and converse piezoelectric behavior of three-dimensionally printed polymer without filler or poling, with relevance to monitoring and actuation

The direct and converse piezoelectric effects are useful for stress/strain monitoring and actuation, respectively. We report these effects in 3D-printed (bottom-up stereolithography, 26-46 µm layer thickness) polymer without filler or poling, using a polymer (unmodified photopolymerizable resin) that is not known to be piezoelectric. This means that the piezoelectric behavior is inherent to the printed material. The inherent behavior is due to the process-induced 2D in-plane shear stress encountered by the resin during printing and the consequent 2D in-plane molecular alignment. The smaller is the layer thickness, the greater is the shear stress, the more is the molecular alignment, and the stronger is the piezoelectric effect. The out-of-plane piezoelectric coupling coefficient is up to 0.43 pC/N - higher than values previously reported for 3D-printed polyvinylidene fluoride, which is known to be piezoelectric.