Flexoelectric enhanced film for an ultrahigh tunable piezoelectric-like effect

Recent advancements in electromechanical coupling effects enable electromechanical materials in soft and stretchable formats, offering unique opportunities for biomimetic applications. However, high electromechanical performance and mechanical elasticity hardly coexist in soft materials. Flexoelectricity, an electromechanical coupling between strain gradient and electric polarization, possesses great potential of strain gradient engineering and material design in soft elastomeric materials. In this work, we report a flexoelectric enhanced elastomer-based film (FEEF) with both high electromechanical capability and stretchability. The integrated strategies with biaxial pre-stretch, crosslinking density of the elastomer along with nanoparticle size, particle filling ratio and electric field charging lead to an enhanced flexoelectricity by two orders of magnitude. Furthermore, this FEEF reveals an ultrahigh electromechanical performance by flexoelectric enhancement with its mechanical design. As a representative demonstration, an ultrahigh piezoelectric-like sensing array is fabricated for multifunctional sensing applications in strain, force and vibration, verifying an equivalent piezoelectric coefficient d₃₃ value as high as 1.42 × 10⁴ pC N^-1, and an average d₃₃ value of 4.23 × 10³ pC N^-1 at a large-scale deformation range. This proposed ultra-high piezoelectric-like effect with its approach is anticipated to provide a possibility for highly tunable piezoelectric-like effect by enhanced flexoelectricity and mechanical design in elastomeric materials.