Freezing and Melting Transitions under Mesoscalic Confinement: Application of the Kossel–Stranski Crystal-Growth Model

Abstract

The Kossel–Stranski model of crystal growth has been adopted to study freezing and melting of fluids in mesoporous materials. The model is found to exhibit the key features observed in the experiments, including shifted solid–liquid and liquid–solid transition temperatures, irreversibility between freezing and melting, and strong impact of the pore geometry. By first analyzing fluids confined to cylindrical pores, we obtain several important insights into the transition mechanisms. In particular, we establish the conditions for the occurrences of equilibrium and metastable transitions and derive exact analytical equations interrelating the transition temperatures, confinement size, and the interaction parameters of the Kossel crystal. Variation of the channel diameter along the channel axis, mimicking disorder in real porous materials, is shown to strongly affect both freezing and melting. The model predicts that the freezing transition in disordered materials is governed by the pore blocking mechanism. The melting transition is found to result as an interplay of two different transition mechanisms.