Piezoelectrets from Cyclic Olefin Copolymers with Different Mechanical and Thermomechanical Properties: A Comparative Study

This paper reports on the fabrication and characterization of piezoelectrets using three types of cyclic olefin copolymers (COCs). The COCs (COC 6017, 6013, 8007) differ considerably in their glass transition temperatures, thermal stability, and mechanical flexibility. The piezoelectrets were fabricated using a carbon dioxide-assisted assembly of a multi-layer non-overlapping structure followed by contact charging. The piezoelectricity was characterized by quasi-static piezoelectric coefficients. Piezoelectrets from the three COCs all showed excellent piezoelectric activity with the quasi-static piezoelectric coefficient reaching up to 1600 pC/N. The thermal stability of the three types of piezoelectret was investigated by thermally stimulated discharge (TSD). The discharge peaks for 6017, 6013, and 8007 were found to be around 210 o C, 180 o C, and 130 o C, respectively. The electrical and electromechanical characteristics of the piezoelectrets were further probed by electric hysteresis loop measurements, butterfly loop measurements, and dielectric resonance spectra for all three types of materials. The study provided the first systematic and comprehensive investigation of the potential of the family of COC copolymers in piezoelectric applications, broadening the materials choices and design space of porous polymer-based piezoelectric materials.