High electromechanical response from bipolarly charged as-electrospun polystyrene fiber mat

Abstract

Electromechanical micrometer/submicrometer polymer fibers are promising components for wearable pressure sensors because the fibers are mechanically flexible, lightweight, and breathable. Although piezoelectric polymers are normally used as their materials, electrospun fibers of some nonpiezoelectric polymers have exhibited high electrical actuation, similar to the inverse-piezoelectric effect of piezoelectric materials. However, the pressure sensing properties and the origin of the behavior of the fibers have been unclear. This study demonstrates the electromechanical properties of an as-electrospun fiber mat composed of a nonpiezoelectric polymer, atactic polystyrene, and analyzes the origin of the properties. The fiber mat demonstrates a high apparent piezoelectric constant (d ) of 950–1400 pC/N with an applied load of 0.05–0.28 N, and a Young’s modulus of 6.40 kPa indicates a soft nature. The surface potential of the stacked fiber mats with forward and opposite stacking confirms that the mat was charged with bipolar and uneven electric charges. This unique charge distribution is the likely origin of the fiber mat’s electromechanical properties. The generated electric charge increased linearly with increasing indentation depth, which can be explained using a theoretical model of bipolarly charged polymer layers and air gaps, similar to the theoretical model of cellular ferroelectrets. This result also supports the bipolarly charged model, and the theoretical model implies that the high d results from the soft and modestly charged nature of the fiber mat. This finding will pave the way for the development of soft, lightweight, and breathable wearable pressure sensors from a variety of materials with high electromechanical performance.