Surface and bulk melting of colloidal glasses

The glass-to-liquid transition, i.e. glass melting, has been poorly studied at the single-particle level. Here we experimentally study the microscopic kinetics of melting in glasses composed of colloidal spheres with either tunable size or attraction. The glasses formed by vapor deposition and quenching exhibit surface and bulk melting, respectively. For surface melting, the structural and dynamic parameters saturate at different depths, which define two surface layers. The thicknesses of both layers grow in a power law as approaching the glass transition temperature, similar to crystal premelting although crystal only has one surface layer. The measured single-particle kinetics reveal various features which follow Landau theory of premelting. Thus, the concept of premelting could be generalized to amorphous solids [1]. For the bulk melting, the observed shrinkage of subcritical nuclei supports nucleation process. The top three most important structural features can effectively predict the nucleation sites, implying heterogeneous melting. At a high defect density or high heating temperature, the melting becomes catastrophic [2].