(376ai) High-Pressure Phenomena in Adsorbed Films: A New Route to an Experimental Determination of Effective Tangential Pressure
AIChE Annual Meeting
2019 AIChE Annual Meeting
Computational Molecular Science and Engineering Forum
Poster Session: Computational Molecular Science and Engineering Forum (CoMSEF)
Tuesday, November 12, 2019 - 3:30pm to 5:00pm
While the normal pressure is uniquely defined for a planar surface, the tangential pressure at a point r is not uniquely defined at the nanoscale. In the commonly used âvirial-routeâ the average of the intermolecular forces acting in the direction parallel to the surface is obtained. The resulting tangential pressure then depends on the fraction of these forces that are assigned to a particular point in space, r. We show that by integrating PT(r) over a small region of space, roughly the range of the intermolecular forces, we obtain an effective tangential pressure that is unique and well-defined. The grand canonical Monte Carlo simulation results show that this characteristic integration range has negligible correlation with the wetting parameter, which denotes the strength of the solid-fluid interaction, and the characteristic length remains as a constant for large pores. Further investigation reveals that the characteristic length of convergence is related to the density distribution of adsorbed layers, which explains its weak dependence on the wetting parameter. Based on this characteristic length, we propose a new route, the â2D-routeâ, to the effective tangential pressure free from the ambiguities in the definition of the âvirial-routeâ local tangential pressure. The only input parameter for this â2D-routeâ is the molecular cross-sectional area. In practice, we can obtain the input parameter by combining standard experimental adsorption data with a 2D equation of state derived from statistical mechanics. We expect this â2D-routeâ to be the first experimental route to the pressure enhancement in the adsorbed layers.