Crystallinity regulated flexoelectricity in cellulose membranes

Abstract

Compared to ferroelectric ceramics, polymers exhibit lower flexoelectric coefficients but offer superior processability and flexibility, making them attractive for deformable electromechanical systems. Cellulose, a biodegradable and biocompatible polymer, is a promising candidate for materials with controllable flexoelectricity. Nevertheless, the intrinsic flexoelectric properties of cellulose remain unexplored, with key influencing mechanisms barely understood either. It is notable that cellulose exhibits a typical crystalline–amorphous dual-phase configuration, making polarization behavior in cellulose strongly depends on the proportion and microstructure of crystalline regions. Therefore, this work located crystallinity as a vital structural parameter in cellulose membrane and unraveled the regulation law of crystallinity on flexoelectric properties. As crystallinity in cellulose membranes increases, which is determined by three independent methods (Segal peak height method: 79.46%–91.37%; peak fitting method: 60.35%–73.09%; FTIR method: 23.21%–44.03%), the flexoelectric coefficient correspondingly rises from 7.33 ± 2.01 to 22.25 ± 1.35 nC/m, revealing a clear linear positive correlation. This trend is found to be independent of the dielectric and piezoelectric properties, suggesting a mechanism related to crystallinity-regulated variations in dipole reorientation. The cellulose membranes also display high mechanical properties, optical transparency, and shapeability. These findings elucidate the essential role of crystallinity in cellulose flexoelectricity and provide crucial insights for the design of high-performance sustainable flexible electronic devices.