Chemical and physical changes associated with high-strain electrostriction in beta-irradiated PVDF-TrFE

In 1998, Zhang et al. [1] demonstrated that large doses of high-energy beta radiation could transform certain vinylidene fluoride-trifluoroethylene (PVDF-TrFE) copolymers into high-strain electrostrictors. Since that time, U.S. Navy researchers and their colleagues have been analyzing irradiated PVDF-TrFE copolymers to determine what physical and chemical changes are associated with the materials' desirable high-strain electrostrictor properties. The most obvious radiation-induced structural change is the introduction and retention of more gauche-type linkages in the PVDF-TrFE polymer chains at room temperature as evidenced by FT-IR spectroscopy, and X-ray diffraction data. These additional gauche linkages function as defects in the long, all-trans sequences normally found in PVDF-TrFE copolymers and, in effect, break up those sequences into the nano-polar domains necessary for high-strain electrostriction. The key role played by the beta radiation in this scenario appears to be the introduction of chemical changes (pendant groups, cross-links and carbon-carbon double bonds) that preserve a higher percentage of gauche linkages below the polymer's Curie temperature. TGA, TGA-MS, 19-F NMR, FT-IR, and DMA data supporting the existence of these beta radiation-induced chemical changes will be presented. This research has important implications for synthetic polymer chemists interested in improving the existing materials and/or creating new, high-strain polymeric electrostrictors with or without the use of beta radiation.