Thermodynamic approach to liquid-to-glass transformation as an arrest transition in polydisperse solution

Abstract

Thermodynamic multi-component solution solidification approach to liquid-to-glass transition is proposed and actual mechanisms underlying vitrification, other than viscous slowdown, are identified. Due to polydisperse aggregation in liquid state, glass-forming liquids, irrespective of chemical composition, appear to be mixtures of various quasi-components whose thermodynamic quantities shall be expressed not in terms of molar concentrations of actual chemical components, but in terms of relative concentrations of dominant structural units. Thermodynamically, any glass-former is expected to behave as multi-component solution and solidify in continuous temperature range between apparent liquidus and solidus temperatures that can be identified as glass-transition range. Using extended irreversible thermodynamics of polydisperse solutions it is demonstrated that upon quenching, diffusional and Brownian mass transport in such solutions is negated within heat removal timescale, which results in dynamical arrest of nucleation and growth in clusters and solid-liquid phase separation. Rapid solution solidification proceeds via successive cluster freezing in continuous temperature range, in line with cluster size dispersity, which can be described in terms of percolation in static polydisperse fractal ensemble where glass transition temperature naturally emerges as percolation threshold. Multi-component solution solidification framework is shown to be reconcilable qualitatively and quantitatively with the Mode Coupling - Random First Order Transition scenario. Finally, it is demonstrated that liquid-to-glass transformation is thermodynamic liquid-to-solid phase transition, glassy state of matter appears to be solid supersaturated solution of defects in otherwise perfect matrix, and the true equilibrium structure which glass is unable access is a crystalline one.