Abstract
X-ray scattering measurements over the angular range 2–30 mrad are reported for a uniaxially oriented poly(vinylidene fluoride) film containing the phase I crystal polymorph. Each intensity profile exhibits at ∼10 mrad an interference peak arising from quasiperiodic variation in electron density between crystalline and amorphous phases of the polymer. Over the temperature range 25–72 °C, reversible changes of 23% in peak intensity and 6% in peak position are observed. These reversible changes in x-ray scattering are analyzed in terms of a one-dimensional stack of alternating crystalline and amorphous layers. These model calculations show that the observed changes in the interference peak cannot be explained solely by thermal expansion within the two phases. In accordance with previous studies on other semicrystalline polymers, this discrepancy between observed scattering results and the predictions for thermal expansion is taken to be evidence that the crystallinity changes reversibly over the investigated temperature range. This evidence for reversible crystal melting is consistent with a hypothesis proposed by Kepler and Anderson to explain the pyroelectric response of polarized, phase I poly(vinylidene fluoride) films.
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