A Lattice Model of Vitrification and Gelation

In this work we introduce a simple lattice model with T-shaped molecules in two dimensions that exhibits a rich range of morphological behaviors. Depending on the volume fraction and quench path, this system can adopt uniform liquid, solution, and phase-separated states, as well as inhomogeneous glass or gel-like states, as revealed by dynamic mean-field simulations. An important characteristic of this system is the existence of a large number of degenerate low-energy states with small barriers that leads to a broad, kinetically explored landscape. The mean-field stability and phase diagram of this model is constructed and provides a useful guide for understanding the complex behaviors of the system. One striking feature is that there is a cascade of instabilities that converge to mark the onset of what we identify as the glass transition. Both dynamic mean-field and Monte Carlo simulations reveal glass-like relaxation dynamics. Our results lead to a picture of gelation as a continuation of the glass transition into the two-phase region, or equivalently, as an incomplete phase separation arrested by the onset of the glass transition.