Glass transition takes place for almost all materials when it is cooled from the liquid state fast enough to avoid crystallization. Although the universality of glassy behaviors is often emphasized across different types of glass-forming systems from structural to spin glasses, the fundamental difference between them is still poorly realized. We will start with a discussion on this point and specify what kind of “glass transition problem” we are going to discuss in this talk.

 For hard-sphere-like glass former, which is a canonical model system of the so-called fragile glasses, we provide a structural approach to the glass transition problem. In particular, a new structural order parameter characterizing local packing capability is defined based on free-energy arguments. We show that the fast relaxation is controlled by the structure at a local level while the slow relaxatiuon is controlled by structural ordering at static correlation length . A quantitative Vogel-Fulcher-Tammann (VFT)-like relation between the relaxation time and the structural order parameter is further established both macroscopically and microscopically at a particle level. These results highlight the basic roles of hidden structure ordering and the nonlocal scenario of structure-dynamics correlation in the glass transition problem.

 However, one should proceed with caution. The nature of glass transition is fundamentally linked to the ultimate fate of liquids upon supercooling. Therefore, special attention has been paid to possible crystallization or phase separation, two well-known fates of most glass formers. For an extraordinary good glass former developed recently, we identify exotic microphase separation at low temperatures, a third possible fate of glass formers, which is inaccessible through ordinary structural or thermodynamic characterizations. Indications one the roles of structure ordering and ergodicity breakdown in the basic understanding of glass transition are discussed accordingly.  

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