Freezing behavior in porous materials: Theory and experiments

We report both experimental measurements and molecular simulations of the m elting and freezing behavior of simple fluids in porous media. Activated ca rbon fibers, having a mean pore width of 1.7 nm, were chosen as the porous medium. Differential scanning calorimetry (DSC) and dielectric relaxation s pectroscopy (DS) were used to determine the melting point in these material s. The melting point was found to be very sensitive to the relative strengt h of the fluid-wall interaction compared to the fluid-fluid interaction. Mo nte Carlo simulations and Landau free energy formalism were used to determi ne the shift in the melting point, T-m, for simple fluids in pores having r epulsive, weakly attractive and strongly attractive walls. The strength of the interaction of the fluid with the pore wall is shown to have a large ef fect on the shift in T-m, with T-m being reduced for weakly attracting wall s. The theory of corresponding states is used to compare the experimental r esults for several systems to the simulation results. This approach also pr ovides a unified approach in understanding the diverse freezing behavior in porous media.