Reducing mechanical brittleness in ferroelectric P(VDF-TrFE) copolymer films via beta radiation

摘要

Copolymers of vinylidene fluoride and trifluoroethylene, P(VDF-TrFE), are capable of converting acoustic energy into electrical signals and vice-versa. The U.S. Navy presently uses P(VDF-TrFE)based sensors (TB-29 towed array), and many concepts for "next generation" transducers and hydrophones for 21/sup st/ century naval platforms can only be realized through the use of electroactive polymers. Annealing, a processing technique used to enhance piezo properties in P(VDF-TrFE) films, also tends to render them brittle. Enhanced brittleness appears to be tied to increases in the average size of the polymer crystallites. The introduction of defects into P(VDF-TrFE) crystallites might reduce/eliminate brittleness by preventing large crystallites from forming. Two defect introduction techniques, beta radiation and chemical synthesis, are being explored for their brittleness reduction potential. Beta radiation increases fracture toughness, but the absorbed dose must be carefully controlled to minimize the destruction of the ferroelectric domains. Certain chemical reactions can also be used to attach bulky side groups to P(VDF-TrFE) polymer backbones (and thereby disrupt the crystallites by forcing the polymer chain farther apart), but their efficiencies are low at the present time. This study shows that it is possible to produce toughened, non-brittle ferroelectric P(VDF-TrFE) copolymer film through the use of beta radiation and the effect is both energy and dose dependent. Lower doses (30 Mrad) of higher energy (2.55 MeV) beta particles produce the best results.