Adsorption and dynamics in cylindrical pore: Molecular dynamics and classical density functional theory study

Abstract

In this work, we investigate the adsorption of single-component and binary neutral fluids in cylindrical pore using molecular dynamics simulations combined with classical density functional theory (cDFT). For the binary case, we also consider scenarios where one component exhibits a non-spherical structure. We investigated the density distribution curves of fluid components in the pore and found that the cDFT calculations without any adjustable parameter yielded results consistent with molecular dynamics simulations. This consistency becomes more pronounced as the temperature increases. At lower temperatures, the theoretical accuracy declines, but it still remains quantitatively reliable. We have developed a method for calculating diffusion coefficient in porous media involving exchange of particles between the exterior and interior of the pores, and applied the method to compute the diffusion coefficients for molecules from outside to inside the pore, as well as within the pore itself. Based on the calculated diffusion coefficients, we can draw several main conclusions: intrapore diffusion along the axial direction always decreases with increasing pore radius; increasing the surface force field strength enhances diffusion in narrow pores while reducing it in wider pores. Moreover, increasing the attraction strength between particles consistently leads to slower diffusion. These findings provide valuable insights into the factors affecting the diffusion process and can be used to optimize porous materials for various applications.