単純分子ガラスの熱力学的研究

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We have combined our recent calorimetric works on vapor-deposited simple molecular glasses and our previous works on ordinary molecular glasses to investigate the universal thermodynamic feature of molecular glasses. Following a brief review for the studies on glass transitions, we describe how the vapor-deposition method is useful for simple molecular glasses. Then, we mention the structure of the adiabatic calorimeter recently developed for vapor-deposited samples. The heat capacities Cp of vapor-deposited carbon tetrachloride (CCl4), propene (CH2=CHCH3) and propane (CH3CH2CH3) are shown. Low-energy excitations characteristic to glasses were observed in all glassy samples. Glass transitions appeared in propene and propane at 56 K and 45 K, respectively; 45 K is the lowest record of Tgs of molecular glasses. The configurational heat capacity ΔCp and entropy Sc are calculated from the Cp data of ten molecular glasses. The universal feature for the temperature dependence of ΔCp is demonstrated by scaling temperature using the Kauzmann temperature TK. The size z* of cooperatively rearranging region (CRR) is also calculated based on the Adam-Gibbs theory. They are increasing with decreasing temperature and frozen at each Tg. The frozen numbers z*(0) are 3-7 molecules and depend on (Tg-TK)/TK; the larger (Tg-TK)/TK is, the smaller z*(0) becomes. Thus, the present work has demonstrated the universal thermodynamic feature of molecular glasses and indicated the validity of the Adam-Gibbs theory based on the experimental data.

単純分子ガラスの熱力学的研究

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