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

The thermal conductivity 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 kappa(T), for both glass and crystal states. The kappa(T) for the glass shows for 1-propanol an anomalously large plateau region comprising temperatures within 6-90 K, while data for isomeric 2-propanol show only a small plateau up to 10 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.