Behavior of Vapor-Deposited Molecular Glass and Supercooled Liquid Obtained through Glass Transition from the Glass

In this paper, we briefly overview first the preceding studies on molecular glasses prepared by vapor deposition on a cold substrate, and then explain our recent studies on such molecular glasses and the supercooled liquids (SCLs) obtained from these glasses through glass transition. Glasses of some of alkylbenzene derivatives prepared at the deposition temperatures (T(d)s) much lower than the glass transition temperature (T-g) show a large excess volume, and undergo a relaxation accompanied with a volume shrinkage in a narrow temperature region just below T-g when the temperature was raised with a constant rate. These samples also undergo a relaxation in the SCL states from a low-density unstable SCL to another SCL. On the other hand, glasses of the same alkylbenzene derivatives prepared by the deposition at T(d)s close to T-g show a molar volume smaller than that expected for the equilibrium SCLs of these compounds, and undergo a relaxation accompanied with a volume expansion in a narrow temperature region just below T-g. Some of these samples undergo a relaxation in the SCL states showing a gradual expansion in the volume. We discuss such differences in the behavior of vapor-deposited molecular glasses and SCLs in relation to non-equilibrium and local molecular conformations in the samples.