Understanding freezing behavior in nano-porous materials: Free energy simulation studies and experiment

Understanding phase behavior in confined systems has the potential to improve the efficiency of a variety of separation processes that use porous materials such as activated carbons, controlled pore glasses, silica xerogels and aerogels, carbon aerogels and zeolites. The effects of the reduced dimensionality and enhanced energetic interactions due to the porous surface have important consequences that can only be captured by molecular level modeling. Novel phase transitions can result (capillary condensation in quasi-one-dimensional systems and orientational ordering transitions in quasi-two-dimensional systems), and often are the cause of the breakdown of macroscopic approaches like Kelvin and Gibbs-Thomson equations based on classical thermodynamics. In this work, the focus is on a free energy method based on Landau theory, and applications of this theory to understand the breakdown of the macroscopic equations, to develop global phase diagrams, and to characterize hexatic phases. Complimentary experimental studies provide supporting evidence for our modeling efforts.