Molecular relaxation and excess entropy in liquids and their connection to the structure of glass

Abstract

We have examined the nature of glass formation in three fragile glass forming liquids, viz., o-terphenyl, phenylsalicylate, and α-phenyl–o-cresol using heat capacity and dielectric relaxation (106–10−3 Hz) measurements. Dielectric relaxation rates and excess entropies of the equilibrium liquid are determined. The temperature dependence of these quantities suggest that the underlying glass transition process (of which the transition at Tg is a kinetic reflection), is possibly nonideal. And also we have studied the structure of the glass of one of the above three liquids, viz., o-terphenyl using dipolar solutes by dielectric spectroscopy and the results are compared to that of the dipolar solutes in their own matrix. Our results indicate that the glasses are statistically uniform materials and all the solute molecules contribute to the secondary relaxation. The role of molecular size and shape in this context is discussed.