Effect of the fluid-wall interaction on freezing of confined fluids: Toward the development of a global phase diagram

We report molecular simulation studies of the freezing behavior of fluids i n nano-porous media. The effect of confinement is to induce spatial constra ints as well as energetic heterogeneity on the confined fluid, thereby alte ring the bulk phase behavior drastically. We consider the effect of the flu id-wall interaction energy on the shift of the freezing temperature and on the fluid structure, using a novel approach to calculate the free energy su rface based on Landau theory and order parameter formulation. Corresponding states theory is then used to map out the global freezing behavior of a Le nnard-Jones (LJ) fluid in model slit-shaped pores of varying fluid-wall int eraction strengths. Using LJ parameters fitted to thermophysical property b ehavior, we predict the qualitative freezing behavior for a variety of flui ds and nano-porous materials, based on a global freezing diagram. We have a ttempted to verify these predictions by comparing with experimental data fo r several systems, and show that in these cases, the experimental observati ons and the predictions are in agreement. (C) 2000 American Institute of Ph ysics. [S0021-9606(00)50121-4].