Deformation and fracture behavior of poly(vinylidene fluoride-trifluorethylene) ferroelectric copolymer films under uniaxial tension

The deformation and fracture behavior under uniaxial tension was characterized for P(VDF-TrFE) 68/32 mol % copolymer films prepared under two different processing conditions. It was found that the copolymer films prepared by solution casting and then annealing show a typical polymeric brittle fracture feature. For the copolymer films prepared by stretching the solution-cast films and then annealing process, a typical linearly strengthening stage occurs in the stress-strain curve after yielding, and the polymer film samples fracture at a much larger maximum strain and a higher tensile strength than those prepared by the former process. SEM observation and XRD analysis were carried out to examine the morphology and microstructure change during uniaxial tension. The results show that for the stretched film samples, the polymer chains undergo slipping or further reorientation during uniaxial tension, causing the increase of the peak intensity in the X-ray diffraction pattern. For the directly annealed ones, no yielding phenomenon is observed and there is no apparent X-ray diffraction intensity change. It was suggested that the highly-oriented fibril structure of the stretched film samples contributes to the linearly strengthening stage after yielding in the stress-strain curve. (c) 2005 Wiley Periodicals, Inc.