PIEZOELECTRIC FOAMS BASED ON CYCLIC OLEFIN COPOLYMER Hui Wang, Yan Li, and Changchun Zeng* High-Performance Materials Institute Department of Industrial and Manufacturing FAMU-FSU College of Engineering Tallahassee, FL, 32311 zeng@eng.fsu.edu Abstract The preparation and characterization of a new type of highly efficient pseudo-piezoelectric materials (ferroelectret) based on porous cyclic olefin copolymer (COC) is reported in the study. The quasi-static piezoelectric coefficient of the ferroelectrets can reach exceptionally high level ~1100 pC/N, and the materials retains the high piezoelectric activity for temperature up to 170 o C. The sample preparation procedures can be divided into three steps. First, patterns on COC film were prepared using laser cutter. Then CO 2 bonding was used to bond different layers together. Finally, contact charging was implemented to obtain desired piezoelectricity. The piezoelectricity was characterized by quasi-static piezoelectric coefficient. Moreover, thermally stimulated discharge was selected to study the thermal stability of the ferroelectret. And hysteresis loop measurements were used to study the charge build up process inside the artificial void. The critical breakdown voltage of the 50µm artificial void sample is about 2500V and agrees with the value calculated from the simplified model. Such material have applications on sensing, actuating and energy harvesting and many other fields. Introduction Piezoelectric materials convert mechanical energy to electric energy. Currently the dominant work material is ceramic based piezoelectric materials. Polymer ferroelectret was investigated in Finland since 1989[1]. Polymer based piezoelectric foams have advantages compared to traditional piezoelectric materials such as flexible, environmentally friendly, lightweight and low cost. A large variety of applications are available for polymer ferroelectret, such as flexible sensor[2][3], actuator[4], musical pickup[2], and microphone[5]. Although significant work has been conducted in regard of different materials[6-11], the thermal stability of the charged polymer foams still requires further study. For example, the dominant working piezoelectric foam, polypropylene piezoelectric foams, only have a working temperature of about 70 o C[12]. Cyclic Olefin Copolymer (COC) is an amorphous polymer made by chain copolymerization of cyclic monomers such as norbornene or tetracyclododecene with ethene. COC has excellent processability, environmental stability, low dielectric constant, low dielectric losses and excellent mechanical properties and particularly, good thermal stability. Several studies had been done in regard of the piezoelectric foams of this type of material[8][11]. We had initially proved that, by using a none-overlapped frame structure, which can efficiently convert mechanical energy to electrical energy, the piezoelectric coefficient can be significantly increased[8]. We developed manufacturing procedures in which CO 2 bonding