The effects of interaction range, porosity and molecular association on the phase equilibrium of a fluid confined in a disordered porous media

Abstract

Grand-canonical transition-matrix Monte Carlo (GC-TMMC) is employed to analyse the effects of range of interaction, packing fraction and molecular association on phase coexistence properties of square-well (SW) based fluids in disordered pores. The nature of the phase equilibria were studied inside a repulsive disordered porous media with packing fractions, η _m = 0.05 and 0.10. Three values of the SW attractive well range parameter were studied: λ = 1.5, 1.75, and 2.0. Coexistence number probability distribution reflects the signature of the disordered structure of the porous matrix. Yet, no multiple fluid–fluid transition was observed. The effect of strength of molecular association on coexistence densities, density profile, saturation pressure, and monomer fraction for the SW based dimerizing fluids inside a repulsive disordered media is reported. Association is found to increase as the packing fraction of the matrix increase. Critical properties of these confined fluids are calculated via a rectilinear diameter approach. Fractional shift in the critical temperature linearly decreases with the increase in the attractive well width for non-associating fluids. The rate of decrease in the critical temperature shift increases with the increase in packing fraction. Associating sites are found to suppress the shift in the critical temperature.

Keywords:

• Square-well fluids
• associating fluids
• disordered pores

Acknowledgements

We wish to thank Dr. Sang Kyu Kwak for helpful conversation. This work was supported by the Department of Science and Technology (Grant No. SR/S3/CE10/2006) and Department of Atomic Energy, Govt. of India (Grant No. 2006/20/36/05-BRNS).