Crumpling charged film sizes up the flexoelectric effect

Crumpling a piece of paper generates an electrical response. That’s because dielectric materials exhibit flexoelectricity, becoming electrically polarized under a strain gradient. This flexoelectric effect, however, decreases as the size of the material increases, becoming unnoticeable above the macroscale. This limits the applicability of this effect, such as in the development of energy capture devices with high energy conversion efficiency.

Not all dielectrics are created equal with regard to the flexoelectric effect. Flexoelectrets are dielectrics that permanently hold charges and can obtain the well-known flexoelectric-like responses through non-uniform deformation. Inspired by flexoelectrets, Ma et al. proposed a method to enhance the flexoelectric effect at the macroscale.

Flexoelectrets show giant flexoelectric-like responses. Crumpling is also known to enhance flexoelectricity. The authors combined these two ways to boost the flexoelectric effect in their method: a crumpled flexoelectret film.

They developed a theoretical model for a crumpled flexoelectret film and analyzed its flexoelectric-like response under different thicknesses, charge densities, and scales. Its flexoelectricity was noticeable at the macroscale, indicating the flexoelectric effect is no longer size-limited.

They found the flexoelectric-like response can be tuned by changing the film’s thickness and charge density. At 1 mm, with a charge density of −0.2mC·m−2, the flexoelectric-like response of the crumpled flexoelctret film was nearly 100 times higher than its intrinsic flexoelectricity.

“Our work allows the flexoelectric effect to break through the size limit and become appreciable at the macroscale,” said author Binglei Wang. “Moreover, it provides new design guidelines for improving the flexoelectric effect at a broader scale.”

Next, the authors will attempt to verify their model through experimentation on crumpled flexoelectret films.

Source: “Crumpling electret films for a stronger macroscopic flexoelectric response,” by Jianhua Ma, Lingling Chen, Jinrui Xu, Shengyou Yang, and Binglei Wang, Journal of Applied Physics (2023). The article can be accessed at https://doi.org/10.1063/5.0147879 .