Diffusivity of CH₄ In Model Silica Nanopores: Molecular Dynamics and Quasichemical Mean Field Theory

Abstract

Equilibrium molecular dynamics and dual control volume grand canonical molecular dynamics experiments were carried out aiming at the investigation of the dependence of transport diffusivity upon the adsorbent pore size and sorbate concentration of CH₄ in cylindrical silica nanopores at 298 K, calibrated with respect to experimental data of zeolite VPI 5; the results of simulation were elaborated on the basis of the quasichemical mean field approximation via a theoretical model for surface diffusion. Our mapping procedure between simulation and quasichemical theory reveals that sorbate–sorbate energetics emerge as the physical reason for the variation of corrected (Darken) and hence transport diffusivity with respect to pore size and sorbed phase fractional occupancy.

Keywords:

• Molecular dynamics
• Dual control volume grand canonical molecular dynamics
• Nanopores
• Transport diffusivity
• Corrected diffusivity
• Quasichemical mean field approximation

Acknowledgements

I wish to express my gratitude to Prof. David Nicholson for his invaluable support on the DCV GCMD technique during my stay at Imperial College. This work was partially supported by the European project TROCAT (Contract No. G5RD-CT-2001-00520).