Adsorption of fluids in a pore with chemical heterogeneities: The cooperative effect

Abstract

In this work, we study the cooperative adsorption of fluids in a heterogeneous pore, in which the pore walls are composed of homogeneous substrates with chemical groups (CGs) decorating them. The adsorption caused by the homogeneous substrates alone and that by CGs do not add up to the overall adsorption, indicating the existence of a cooperative effect. The cooperative effect is the source of cooperative adsorption, and is characterized in this work by the ratio of the overall adsorption to the sum of adsorption by the substrate only and that by CGs. It is found that the cooperative adsorption does not depend monotonically on the substrate or the CGs. Two different origins of the cooperative adsorption play different roles depending on which one dominates the overall adsorption. Our simulations reveal that, when the homogeneous substrate dominates the overall adsorption, weakening of the attractive fluid-substrate interaction or alternatively strengthening of the fluid-CGs interaction leads to a stronger cooperative effect and enhances the cooperative adsorption. However, when CGs dominate the overall adsorption, weakening of the attractive fluid-CG interaction or strengthening the fluid-substrate interaction results in strong cooperative adsorption. In order to investigate the effects of the distribution of CGs on cooperative adsorption, a design-test method is generalized and used in this work. Simulation results show that the overall adsorption can be significantly affected by the CG distribution.

A thermodynamic scaling Monte Carlo method to determine the unlike pair interaction parameter

“…Computer simulation and density functional theory have been widely applied in fluid phase equilibrium calculation [16][17][18][19][20][21][22][23][24][25], which the main obstacle in fluid phase equilibrium is simulated parameters [25][26][27].We have proposed a new version of thermodynamic scaling Gibbs ensemble method, the δ -TDSGE method, in which we can sample configurations over a certain unlike-pair interaction potential parameter range of the LJ potential. As is shown in equations (9-b) and (11), the sampling weights for the configurations can be determined simply by calculating the free energy difference between two states.…”

Bulk supercooled water versus adsorbed films on silica surfaces: specific heat by Monte Carlo simulation

“…[43][44][45][46][47][48][49][50][51][52] It is well-known that the chemical and morphological disorder of the adsorbing surface plays a major role in adsorption. [53][54][55][56][57][58] An important issue of water adsorbed on hydroxylated silica surfaces concerns the connection between the three dimensional hydrogen bond network belonging to water with the two-dimensional H-bonds at the water-silica interface. This is expected to have an impact on the heat capacity of adsorbed layers of water through the local dynamics of adsorbed molecules.…”

Molecular simulation study of the heat capacity of metastable water between 100 and 300 K

“…[9][10][11][12][13][14][15][16][17][18] It is well-known that the fluid adsorption is influenced by the chemical disorder of the adsorbing surface. [19][20][21][22][23] In particular, the structure and dynamics of an adsorbed water film has been shown to be influenced by the nature of the silica surface. 15,24 This is expected to have an impact on the heat capacity of adsorbed layers of water, to be studied now.…”