Supercooled and over compressed liquids up to the glass transition: from microscopic to macroscopic points of view

In recent times there has developed an increasing interest in the challenge to liquid state theory offered by the phenomenon of supercooling and glass formation. In the extended temperature range opened up by supercooling and over compressing, a variety of new phenomena are encountered. In particular there is the onset of a remarkable divergent behaviour in the viscosity, and in the relaxation times measured by dielectric, neutrons, specific heat spectroscopy, and light scattering techniques. Recent theoretical efforts have been in the direction of treating the glass transition as a sort of critical phenomenon though success has been limited to the low viscosity region of behavior. In this lecture, we will review some of the measurements which have been made on a series of isostructural liquids in which the strength of H-bonding was systematically increased by change of benzene ring substituants, and wiil discuss their piace in the overall pattern of “strong and fragile” liquid behaviour. Finally introducing the notion of isothermal glass transitions and the related entropic relaxation, we will distinct between thermodynamic and kinetic contributions to the temperature and density dependence of the relaxation times