Dielectric investigations of pure and mixed fluorocarbons in their condensed phases

Abstract

We review recent work and present new results on the liquid and solid fluocarbons CMF 3 with M = H, F, Cl, Br, CH 3, and CF 3. The pure compounds as well as several series of binary mixtures were investigated using dielectric measurements. The permittivities of the non-hydrogenatcd non-polar and polar liquids could be described using the Clausius-Mosotti and the Onsager equation, respectively. In CHF 3 and C 2H 3F 3 hydrogen bridging leads to deviations from this simple behavior. The trends in the miscibility of four series of fluorocarbon mixtures are in qualitative accord with regular solution theory. The geometrical shapes of the compounds dominate the degrees of order below their melting point. Orientational liquid states (or plastic crystalline phases) are exhibited by the quasi-globular halomethanes CF 4 and C 2F 6, whereas complete dipolar order is found for the aspherical compounds CHF 3 and CBrF 3. The dielectric results for solid C 2H 3F 3 indicate a phase transition several degrees below the fusion temperature probably being due to the onset of intramolecular rotation. CClF 3 exhibits thermally activated dipole dynamics in the solid state. In alloys of CClF 3 with CF 4 and C 2F 6 the dielectric loss spectra have signaled single particle reorientations and glassy excitations.