Enhancing the inherent piezoelectric behavior of a three-dimensionally printed acrylate polymer by electrical poling

A three-dimensionally (3D) printed acrylate polymer without filler, printed by stereolithography, has previously been shown to be inherently piezoelectric in the out-of-plane and in-plane directions in the absence of electrical poling. This work has shown that the longitudinal piezoelectric coupling coefficient d is increased by poling at an electric field of 2400 V m^-1 by up to about 200%. The poling takes 60 min for either direction. The effect of in-plane poling on the in-plane piezoelectric effect is greater than the effect of out-of-plane poling on the out-of-plane piezoelectric effect. This is due to the lower piezoelectric coefficient without poling for the in-plane direction, consistent with the fact that the molecular alignment is 2D in the plane of the printed layers and the in-plane poling is conducted in a particular in-plane direction. Without poling, d is smaller for the in-plane direction than the out-of-plane direction. With poling, d is essentially equal for the two directions. This suggests that the in-plane poling possibly causes the in-plane molecular alignment to develop a slight degree (if any) of 1D molecular alignment. The natural depoling that occurs immediately after the completion of the poling takes as little as 60 min, with the depoling being faster in the out-of-plane direction than the in-plane direction. Due to the depoling, the inherent piezoelectric behavior without poling remains practically attractive.