Broadband dielectric studies in linseed oil: Supercriticality and the New Insight into Melting/Freezing Discontinuous Transition

Abstract

The long-range supercritical changes of dielectric constant, resembling ones observed in the isotropic phase of rod-like liquid crystalline compounds, are evidenced on approaching liquid-solid discontinuous phase transition. The 'supercriticality' can be an additional factor for supporting the unique pro-health properties of linseed oil. It can also be significant for numerous technological applications. The report also reveals properties significant for melting/freezing discontinuous phase transition cognitive puzzle. Broadband dielectric spectroscopy studies revealed long-range premelting (heating from the solid phase) and post-freezing (cooling from the liquid phase) effects with critical-like parametrizations. They can be correlated with the 'grain model' for premelting and its development by the Lipovsky model. The evidence for the post-freezing effect, with the critical-like portrayal, may indicate a specific granular solidification associated with pretransitional fluctuations. Numerous hallmarks of liquid-liquid and solid-solid phase transitions have also been found. Notably, the melting temperature surrounding is related to the minimum and the freezing temperature to the maximum of dielectric loss factor D=tan(delta). Regarding dynamics, three primary relaxation processes have been found. Their changes in subsequent temperature intervals, related to the apparent activation enthalpy, follow critical-like patterns with the same singular temperature. For relaxation times evolution, it leads to optimal parameterizations via the 'critical and activated' equation, recently proposed.