Materials and Structural Design Approaches of Intelligent Piezoelectric Fibers for Self-Powered Sensing

Electrospun polymeric piezoelectric fibers have considerable potential for shape-adaptive mechanical energy harvesting and self-powered sensing in biomedical, wearable, and industrial applications. However, their unsatisfactory piezoelectric performance remains an issue to be overcome. While strategies for increasing the crystallinity of electroactive <i>β</i> phases have thus far been the major focus in realizing enhanced piezoelectric performance, tailoring the fiber morphology can also be a promising alternative. Here, we summarize a collection of advances that push the boundaries to achieve a drastic enhancement of self-powered sensing performance by tailoring both material and structural properties of electrospun piezoelectric polymer fibers at multi-scales. As one of the recent advances, we demonstrate a distinctive design strategy for fabricating P(VDF-TrFE) fibers with surface porosity under ambient humidity conditions via nonsolvent-induced phase separation (NIPS). The key aspect of this material design is the porosity engineering of electrospun piezoelectric polymer fibers. Considering the thermodynamic properties of the P(VDF-TrFE) polymer solution in combination with the kinetics of electrospinning, we successfully implemented surface porosity in the P(VDF-TrFE) fibers under ambient humidity conditions. Notably, electrospun P(VDF-TrFE) fibers with higher surface porosity outperform their smooth-surfaced counterparts with a higher <i>β</i> phase content in terms of output voltage and power generation. Further engineering structural morphology of piezoelectric materials from molecular to fiber and yarn structures will be discussed as a route to achieving improvement in the key figures of merit for energy harvesting and sensing, along with our unfolding new understanding of the underlying physics.