Study on flexoelectric properties and sensing applications of CS-PVA-IL/BaTiO₃ composite ionic gels

Conventional piezoelectric devices struggle to effectively detect bending strain gradients induced by joint motion, limiting their applicability in wearable health monitoring. Therefore, there is an urgent need to develop sensors with high sensitivity to bending deformation for efficient detection of dynamic human motion signals. In this study, a flexoelectric sensor was designed and fabricated based on a chitosan-polyvinyl alcohol-ionic liquid (CS–PVA–IL) composite ionogel incorporating BaTiO₃ nanoparticles. The influence of BaTiO₃ content on the flexoelectric response was systematically investigated. When the BaTiO₃ concentration reached 0.25 wt%, the sensor exhibited a high output voltage of 1.8 V and a flexoelectric coefficient of up to 1.92 nC/m, demonstrating excellent flexoelectric performance. The fabricated sensor showed outstanding linear response and cyclic stability. During wearable applications, distinct output signals were observed in response to wrist and index finger bending, and the peak voltage correlated well with bending amplitude. These results validate its practical utility in health monitoring. This work offers new insights into the electromechanical transduction mechanisms of flexible sensors and lays a solid foundation for applications in smart wearables and bioelectronics.