Effects of resonant phonon scattering from internal molecular modes on the thermal conductivity of molecular glasses

Abstract

The thermal conductivity $\ensuremath{\kappa}(T)$ of the crystalline and glassy phases of the two isomers of propyl alcohol has been measured. The two isomers differ by a minor chemical detail involving the position of the hydroxyl group with respect to the carbon backbone. Such a difference in molecular structure leads, however, to disparate behaviors for the temperature dependence of $\ensuremath{\kappa}(T)$, for both glass and crystal states. The $\ensuremath{\kappa}(T)$ for the glass shows for 1-propanol an anomalously large plateau region comprising temperatures within $6--90\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, while data for isomeric 2-propanol show only a small plateau up to $10\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ which is comparable to data on lower alcohols. The results emphasize the role played by internal molecular degrees of freedom as sources of strong resonant phonon scattering.