Origin of the heat-capacity/onset-temperature behavior in vapor-deposited glasses

Determine why the correlation between heat capacity and onset temperature observed in vapor-deposited toluene, ethylbenzene, cis-decalin, and cis/trans-decalin glasses is lost at lower substrate temperatures.

Background

The paper compares two properties of vapor-deposited glasses: the onset temperature of transformation into the supercooled liquid, which reflects kinetic stability, and the glass heat capacity. For toluene and ethylbenzene, these quantities are anticorrelated down to approximately 0.80 Tg, with higher onset temperatures accompanying lower heat capacities. At lower deposition temperatures, however, both the onset temperature and heat capacity decrease, so the anticorrelation disappears.

The authors report qualitatively similar behavior for cis-decalin and the 50/50 cis/trans-decalin mixture. They explicitly state that this behavior is not understood and requires further exploration, making the mechanism behind the low-temperature decoupling an unresolved problem.