Energy harvesting δ-phase polyvinylidene-fluoride sponge

Flexible and shrinkable ferroelectric δ-phase PVDF sponge and its unique voltage and capacitance behavior in response to periodic mechanical stress are reported. Depending on the electrical poling field, chain formation of PVDF-PDMS was determined to be δ- or β-phase. For the β-phase PVDF-PDMS material, voltage output was generated only when strain was applied and released. On the contrary, the δ-phase PVDF-PDMS material exhibited pulse-type stable and uniform voltage during periodic pushing. As the PVDF concentration and the pushing depth increased, output voltage increased. In addition, for the δ-phase PVDF-PDMS, a pulse-type capacitance increase was observed repeatedly in response to periodic mechanical stress. Because δ-phase PVDF-PDMS exhibited P-E hysteresis, it is concluded that a flexible and shrinkable ferroelectric δ-phase PVDFPDMS sponge is fabricated. Voltage and capacitance increased with an increase in the amount of total charge induced by ferroelectric polarization at each mechanical stress.