Salient properties of glassforming liquids close to the glass transition

This article is focused on the dramatic increase of the viscosity, or on the relaxation time of supercooled molecular liquids, and on the dynamical arrest observed when the temperature is cooled down to the glass transition temperature T-g at atmospheric pressure and under pressure. After an introduction of the fragility concept due to Angell, the particular super-Arrhenius behavior of the so-called fragile liquids is shown to be temperature rather than density driven. The non-exponential behavior of structural relaxation as a function of time, and the existence of dynamical heterogeneities are presented, whose emergence is related to the possible manifestation of polyamorphism. Some theories of deeply supercooled liquids are tested. (C) 2001 Academie des sciences/Editions scientifiques et medicales Elsevier SAS.