Cellulose-Templated Poly(vinylidene Fluoride) Polar-Phase Microspheres with a Lightweight Structure and Enhanced Piezoelectric Output

The rational design of three-dimensional (3D) piezoelectric architectural units represents a cutting-edge approach for fabricating highly sensitive piezoelectric materials. However, the precise control over the formation of piezoelectric crystals during the construction of 3D polymer architectures remains a formidable challenge. Here, we report a novel strategy that enables the induction of dominant polar forms while simultaneously constructing their 3D architectures. Utilizing porous cellulose templates, poly(vinylidene fluoride) (PVDF) was self-assembled from solution into microspheres with diameters approximately 3 μm. During this self-assembly process, hydrogen bonding and dipole interactions between PVDF molecules and the cellulose template could facilitate the nucleation and growth of the polar forms. By manipulating the porous structure of cellulose, we successfully achieved two distinct spatial arrangements of PVDF polar microspheres: a homogeneous distribution of PVDF polar microspheres interspersed among the cellulose nanofibrils, and the aggregation of PVDF polar microspheres on the cell wall of the template. Our findings reveal that the former arrangement demonstrates superior piezoelectric sensitivity, boasting a piezoelectric voltage constant of 0.42 V·m/N at a low mass density of 0.3 g/cm3─approximately three times greater than that of the pure PVDF and the cellulose template alone. The remarkable piezoelectric sensitivity observed in the 3D porous PVDF/cellulose composite stems from the fact that the compressive stress applied to the polar microspheres induces a substantial effective electric displacement in the direction of the compressive force. This study opens the door to a new class of rationally designed piezoelectric sensors for wearable human-computer interaction applications.