Direct Measurements of Thermodynamic Stability of Melt-Quenched and Vapor-Deposited 1,3,5-Tris-(α-naphthyl)benzene Glasses

The efficient tools for characterization of the amorphous state are key to deepening our understanding of the glass transition phenomenon as well as controlling the conditions of glass production, storage, and exploitation. The thermodynamic stability of glasses is commonly determined by differential scanning calorimetry (DSC) by measuring the heat capacity in the devitrification region. In this way, the fictive temperature, showing the deviation between the glass and the equilibrium liquid, is obtained. Fundamental limitations of such a procedure are the need to extrapolate the temperature dependences of the glass and liquid state heat capacities and the possible interference of crystallization. In this work, we demonstrated that solution calorimetry can be an efficient instrument to determine the relative thermodynamic stability of glasses directly at 298.15 K. Melt-quenched and vapor-deposited glasses of 1,3,5-tris-(α-naphthyl)benzene (TNB) were obtained and studied by DSC and solution calorimetry. The difference between the solution enthalpies in benzene of the melt-vitrified and vapor-deposited glasses was consistent with the data on fictive temperatures obtained by DSC. The enthalpies of the amorphous thin films slowly deposited onto a cold substrate were substantially lower than those of the vitrified melts, in agreement with the recent studies of ultrastable glasses. The results of the study highlight the perspectives of solution calorimetry as a tool for studying the thermodynamic state of glasses that crystallize quickly on heating, including ultrastable ones, and its promising insights into the Kauzmann paradox.