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

Abstract

The thermal conductivity ͑T͒ 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 ͑T͒, for both glass and crystal states. The ͑T͒ 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.

Deuteration effects in the thermal conductivity of molecular glasses

“…G is the dimensionless normalization parameter effectively allowing for the intensity of heat transfer by localized excitations including rotational ones, Θ up and Θ low are the temperatures corresponding to the upper and lower frequency limits for the propagating sound-like waves ω up and ω low , respectively; ω low > ω ВР . The density of C 2 H 5 OH glasses was ρ = 958.2 kg/m 3 [9]. For C 2 D 5 OD glasses the density ρ =1083 kg/m 3 was calculated from the molar volume data, the coefficient being the same as for protonated ethanol.…”

Effects of internal molecular degrees of freedom on the thermal conductivity of some glasses and disordered crystals

“…[1][2][3][4] To unravel the underlying physics, studies on relatively simple molecular systems which can be tailored to show controlled amounts of disorder pertaining to the molecular centers of mass, the relative molecular orientations, or even the molecular conformations that arise from flexible molecular segments showing different orientations with respect to some molecule-fixed frame constitute important benchmarks. [5][6][7] Orientational glasses (OGs) are materials where, in contrast to fully amorphous materials such as the structural glasses (SGs), the centers of mass of the molecules sit on the nodes of a crystalline lattice, keeping the molecular orientations and/or molecular conformations randomized. The beauty of OGs stems from their remarkably close thermal and dynamic properties to those exhibited by amorphous materials.…”

Heat transfer in solid methyl alcohol

“…Polymorphism of the crystalline phases of methanol is governed by its H bonds which are stronger than the dispersive molecular interactions and by its simpler molecular structure in comparison to ethanol. It is found in the previous studies [14][15][16] of thermal conductivity of alcohols (ethanol and isomers of propyl alcohol) in different polymorphous states that ethanol has similar temperature dependence of thermal conductivity (especially at low temperatures) in the phases of a metastable orientationally disordered crystal and a glass (structurally disordered solid). In the propyl alcohols (1-propyl alcohol and 2-propyl alcohol) a strong isomeric effect in the temperature dependence of thermal conductivity was observed.…”