Abstract
The microstructure of the free volume and its high-pressure dependence in fluoroelastomeric copolymers of tetrafluoroethylene (TFE) and perfluoro(methyl vinyl ether) (PMVE), PFE, as well as vinylidene fluoride (VDF) and hexafluoropropylene (HFP), VDF/HFP22, was studied by pressure−volume−temperature experiments (PVT, P = 0.1−200 MPa) and positron annihilation lifetime spectroscopy (PALS, P = 0.1−448 MPa, all at 22.5 °C). Employing the Simha−Somcynsky equation of state the excess (hole) free volume fraction h and the specific free and occupied volumes, Vf = hV and Vocc = (1 − h)V, were estimated from the specific total volume V. The pressure variation of these volumes and their compressibilities are discussed. We found that the occupied volume Vocc exhibits a remarkable compressibility, κocc ≈ 2.4 × 10-4 MPa-1, while it shows (for T > Tg) almost no thermal expansion. The PALS spectra were analyzed using the new routine LT9.0 assuming dispersion in both the positron (τ2) and orthopositronium (o-Ps) lifetime...
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