Structural relaxation and calorimetry in the glass-softening range of 1,3,5-tris(1-naphthyl)benzene

Features of the time- and temperature-dependent heat capacity of 1,3,5-tris (l-naphthyl)benzene (T alpha NB) have been studied by differential scanning calorimetry and analyzed in terms of a formalism for the stretched-exponen tial, nonlinear changes of the fictive temperature, T-f, or enthalpy, H, of its glass. T alpha NB shows a remarkably narrow distribution of structural relaxation times with the stretch-parameter beta of 0.8. The formalism doe s not fit the data for the irreversible relaxation of its glassy state obta ined by rapid cooling. This is attributed to incomplete structural freezing at T-f on rapid cooling of the liquid and a decrease in H, as faster modes of motions also gradually freeze-in on cooling below T-f. Thus, not only H decreases nonlinearly with the temperature but also the heat capacity vari es on irreversible relaxation. Therefore, the formalism does not reproduce the structural states when a change in T-f alone is considered. No differen ce in the reduced temperature width was observed when T alpha NB liquid was rapidly cooled and its glass slowly heated, or vice verse. Samples, anneal ed or slowly cooled, may show an increase in the width, or a decrease, depe nding upon the material's relaxation characteristics. The reduced temperatu re width of the glass-softening endotherm seems to provide an unreliable co rrelation with the temperature dependence of structural relaxation.