Phase transition from liquid to disordered solid phase of cyclooctanone studied with dielectric methods.

The dielectric studies performed for cyclooctanone in its static dielectric regime have shown that at the phase transition from liquid to disordered (plastic) solid phase of the compound, the following singular phenomena occur: (a) the static permittivity (ε(s)) exhibits a small increase at the transition, instead of that usually observed for polar liquids, a strong decrease of the permittivity at the transition to the crystalline solid phase; (b) temperature dependence of the permittivity, ε(s)(T), is practically the same in both phases, reflecting the same dipolar orientational entropy increment induced by the probing electric field; (c) a distinct jump occurs in the slope of the frequency dependence (in log-log scale) of the dielectric losses due to an ionic current, from the "ohmic" value -1 in the liquid phase to about -0.9 just after the transition to the plastic phase; (d) a similar jump is observed in the shape of the electric modulus spectra of cyclooctanone. The results clearly show the liquid-like freedom in the molecular dynamics in the plastic phase as well as similar intermolecular interactions in both phases of cyclooctanone. The differences in the dielectric losses frequency behavior may reflect the change in the ions dynamics: from the normal translational Brownian diffusion in the liquid phase to the subdiffusional dynamics in the plastic phase.