Freezing of mixtures confined in silica nanopores: experiment and molecular simulation.

Freezing of mixtures confined in silica nanopores is investigated by means of experiment and molecular simulation. The experiments consist of differential scanning calorimetry and dielectric relaxation spectroscopy measurements for CCl(4)/C(6)H(5)Br mixtures confined in Vycor having pores with a mean diameter of about D=4.2 nm. Molecular simulations consist of grand canonical Monte Carlo simulations combined with the parallel tempering technique for Lennard-Jones Ar/Kr mixtures confined in a silica cylindrical nanopore with a diameter of D=3.2 nm. The experimental and molecular simulation data provide a consistent picture of freezing of mixtures in cylindrical silica nanopores having a size smaller than ten times the size of the confined molecules. No sharp change in the properties of the confined mixture occurs upon melting, which suggests that the confined system does not crystallize. In the case of the molecular simulations, this result is confirmed by the fact that except for the contact layer, the percentage of crystal-like atoms is less than 6% (whatever the temperature). The molecular simulations also show that the composition of the mixture is shifted, upon confinement, toward the component having the strongest wall/fluid attraction.