Davydova N. Structure of molecular aromatic glasses, solid metastable states, and polymorphism.

The dissertation deals with a study of vitrification of supercooled liquids and formation of the metastable phases using infrared and Raman spectroscopy and differential scanning calorimetry methods. The molecular compounds such as benzophenone, ortho- and parabromobenzophenone, 4,4'- dichlorobenzophenone, 2-biphenylmethanol, and salol were investigated. It was shown that the crystal nucleation of the metastable phase plays a crucial role in the vitrification of supercooled liquids. The crystal embryos/nuclei are generated at Тn ~ 1.2 Тg (Tg is the glass transition temperature) in the course of cooling of the supercooled liquid. These crystalline nuclei lead to dynamic heterogeneity of the supercooled liquid in the temperature interval Тg<Тn<1.2Тg. During subsequent cooling below Тg the fluctuating nuclei become an important element of the glass structure. The occurrence of polymorphism in 2-biphenylmethanol and orthobromobenzophenone was revealed. The crystal structures of two polymorphs of 2-biphenylmethanol were determined. The crystal of the stable phase was shown to be triclinic, space group P1. The molecules form intermolecular hydrogen bonds producing a tetramer local structure. The crystal of the metastable phase belongs to the monoclinic system, space group Pc. The molecules are linked by hydrogen bonds into chains.