Giant electrostrictive response in poly(vinylidene fluoride-hexafluoropropylene) copolymers

Electrostrictive strains were measured in three different polymeric materia ls: a low modulus polyurethane elastomer, previously studied by Scheinbeim et al. [1], and two higher modulus random copolymers of poly(vinylidene flu oride-hexafluoropropylene) [P(VDF-HFP)] with 5% and 15% HFP content. Measur ements at increasing voltage (electric fields ranging from 0 to 60 MV/m) we re taken. using an air gap capacitance system and then converted to sample thickness. Copolymer samples with different thermal histories were compared , ice water quenched, air quenched, and slow cooled, for both compositions. The ice water-quenched 5% P(VDF-HFP) copolymer exhibited the highest strai n response (>4%) with a dielectric constant of 13.9. The previously studied polyurethane elastomer exhibited the second highest strain response, >3%, with the lowest dielectric constant, 8.5. The ice water-quenched 15% HFP co polymer exhibited the lowest strain response among the three polymeric mate rials tested, approximate to 3%, with a dielectric constant of 12.2. The st rain energy density of the 5% HFP ice water-quenched copolymer, 1/2 YSm2(1/ 2 Young's modulus, Y, times the maximum electrostrictive strain, S-max squa red), is the largest known for any semi-crystalline polymer: 0.88J/cm(3).