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 (CCl
4), propene (CH
2=CHCH
3) and propane (CH
3CH
2CH
3) 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 Δ
Cp and entropy
Sc are calculated from the
Cp data of ten molecular glasses. The universal feature for the temperature dependence of Δ
Cp 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.
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