Thermal Conductivity of Metastable States of Simple Alcohols

Abstract

The thermal conductivity κ(T) of glassy and supercooled liquid methanol, ethanol and of 1-propanol has been measured under equilibrium vapor pressure in temperature interval from 2 K to 160 K by the steady-state method. The metastable orientationally disordered crystal of ethyl alcohol is found to exhibit a temperature dependence of κ(T) that is remarkably close to that of the fully amorphous solid, especially at low temperatures. In the case of propyl alcohol, our results emphasize the role played by internal molecular degrees of freedom as sources of strong resonant phonon scattering. For all samples here explored, the glass-like behavior of κ(T) is described at the phenomenological level using the model of soft potentials. The thermal transport is then understood in terms of a competition between phonon-assisted and diffusive transport effects. The thermal conductivity κ is thus a sum of two contributions: κ = κI + κII, where κI is the acoustic phonon component dependent on the translational and orientational ordering of molecules, κII — is the phonon diffusion component corresponding to a non — acoustic phonon heat transfer in accordance with the Cahill — Pohl model.