Character of devitrification, viewed from enthalpic paths, of the vapor-deposited ethylbenzene glasses.

Enthalpic path and enthalpy-relaxation rates of ethylbenzene glasses prepared by vapor deposition at various temperatures, T(D), were examined on heating intermittently with a high-precision adiabatic calorimeter. It was confirmed that when T(D) is in the range 0.79-0.96T(g), the enthalpies elucidated at their preparation temperatures, i.e., T(D), are lower than those of the liquid-cooled glass. The fictive temperature T(f) at which the enthalpy path of each glass crosses the enthalpy curve expected for the equilibrium supercooled liquid was observed to be lowest when T(D) = 0.92T(g) = 105 K. The glasses revealed two remarkable characteristics: first, the temperature of the peak in the endothermic effect, which corresponds to the temperature T(g,dev) of the steepest devitrification, was observed to increase in correlation with the low-enthalpic nature of the glasses. Second, the devitrification manner was quite different between the glasses with T(D) < 0.92T(g) and T(D) ≥ 0.92T(g), even if the two glasses have the same T(f); the former devitrified gradually and the latter relatively sharply.