Improvement of electrocaloric properties of P(VDF-HFP)/GNPs composites for refrigerator cooling

Electrocaloric effect originally comes from the cross-coupling between temperature and polarization of dielectric materials. Poly (vinylidene fluoride)/P(VDF) and its copolymers exhibit high displacement and dielectric properties among all ferroelectric polymers with additional advantages like lightweight, flexible and low cost compared with other dielectric materials. Moreover, poly (vinylidene fluoride hexafluoroprophylene)/P(VDF-HFP) copolymers shows highest breakdown strength. P(VDF-HFP) copolymers was used as the main matrix with graphene nanoplatelets (GNPs) conducting materials as nanofillers. The P/GNPs composites thin films were prepared by solution casting method with the final thickness of 30 +/- 5 µm using N, N-dimethylformamide (DMF) as solvents. The GNPs content was varied of 0, 1, 2, 3, 4 and 5% by weight. The dielectric and electrical properties were measured by LCR meter with various frequency of 1 to 100 kHz. The structure and crystallinity were observed by XRD and DSC. The polarization as a function of external electric field was investigated by P-E loop instrument in 40 MV/m with varying temperature from room temperature to 140 °C. Furthermore, electrocaloric effect was measured by indirect method by calculating adiabatic temperature change (ΔT) with help of Maxwell relation. The experimental results show that dielectric constant of P/GNPs composites was increased by increasing the GNPs content but dielectric loss is kept constant with low loading, far away from the percolation threshold. Moreover, the ΔT of the P/GNPs composites is higher than the pure P(VDF-HFP) copolymers that leads to higher electrocaloric effect. The Increasement of the ΔT of P/GNPs composites will be discussed based on their microstructure, phase transition and crystallinity. As conclusion, adding GNPs nanofillers to P(VDF-HFP) matrix can improve dielectric constant as well as electrocaloric properties which has capability for refrigeration cooling system. (paper)