Flexoelectricity refers to the linear coupling between strain gradient and electric polarization. Due to its ubiquitous existence in dielectric materials, flexoelectricity is promising in electromechanical applications. The fundamental challenge of flexoelectricity is its low electromechanical performance, depending on the flexoelectric coefficient of the materials and the applied strain gradient. Soft materials possess large deformation ability for potential large strain gradient, while the flexoelectric coefficient of soft materials is usually limited. Dielectric elastomers (DE), as a typical soft material, can respond and behave to external electrical or mechanical stimuli, which have been developed as electromechanical transducers. The mechanical versatility enables multiple strategies in the flexoelectric technologies. In this work, we propose a mechanical approach to manipulate flexoelectricity in elastomers by pre-stretch. A theoretical analysis on the mechanical tuning flexoelectricity in crosslinked elastomer is developed. The electromechanical properties of elastomers tuned by pre-stretch and bending are analyzed microscopically and macroscopically. Further, four point bending experiment based on transverse flexoelectric measurement is adopted to verify the theoretical prediction under pre-stretch. Results of silicon elastomer (SYLGARD 184) with different crosslinking densities are all in accordance with theoretical predictions. This study provides a mechanically tunable method in flexoelectricity of elastomer and further promotes the utilization of stretchable materials in flexoelectric applications.

Keywords: flexoelectricity, pre-stretch, strain gradient, electromechanical coupling