Polymeric piezoelectric composites by contact electrification

Piezoelectric polymers hold great promise for applications in flexible electronics and self-powered sensing. However, conventional piezoelectric materials require non-centrosymmetric crystal structures and normally a high electric-field poling. The requirement not only restricts material selection, but also increases fabrication cost and processing complexity of piezoelectric materials. In this study, a strategy for designing polymer piezoelectric composites is proposed by exploiting the contact electrification effect. Three polymers, namely, polytetrafluoroethylene, poly(vinylidene fluoride), and polyamide 6, which have different charge transfer capabilities in the triboelectric series, were used to fabricate polymer composites and demonstrated the viability of the proposed strategy. We show that by simply stacking two polymer disks of different compositions, a piezoelectric-like response can be generated by contact electrification induced by the contact-separation process in the inevitable air gap existing between two disks under a dynamic force (non-intimate contact design). Furthermore, by pressing two polymer films into intimate contact (intimate contact design), a piezoelectric-like response can also be realized due to the change in the density of charge induced by contact electrification under a force. With the two designs, piezoelectric composite metamaterials with an apparent piezoelectric response as high as 126.4 pC/N, which is much higher than that of traditional piezoelectric polymers, were demonstrated. In addition, the new materials are poling-free and independent of crystallographic symmetry. In addition, the piezoelectric response of composites can be sustained at high temperatures > 150 °C. This strategy provides a new design methodology and technological pathway for developing next-generation green and low-cost piezoelectric polymer composites for flexible self-powered sensors and electronic device applications.