Characterization of Cabot BP280 with argon and nitrogen adsorption at temperatures above and below the triple point – Energetic vs Structural heterogeneities

Abstract

Abstract Wetting transitions on surfaces are a ubiquitous phenomenon in nature because the wettability depends on the balance between the adsorbate-adsorbent (which in turn depend on the surface topology), adsorbate-adsorbate interactions and temperature. To understand the separate contributions of these interactions in a wetting transition for a specific adsorbate-adsorbent pair, molecular simulation is an invaluable tool. Here we illustrate this with a detailed experimental and molecular simulation study of argon and nitrogen adsorption on Cabot BP280 at temperatures above and below their respective triple point temperatures. We report new adsorption isotherm data at 60 K and at 87 K and 77 K which confirm previous measurements on this adsorbent. These results were also used to calculate isosteric heats. Our TEM study shows that the surface of BP280 has a geometrically corrugated graphitic structure which is not as planar as highly graphitized thermal carbon black, such as Carbopack F. Simulations were carried out with two models: an energetic model built from strips of different adsorption strength, and a structural model consisting of crevices embedded in a graphite surface. Adsorption at temperatures below the triple point facilitates the probing of the fine details on the surface, enabling the discrimination between the energetic and structural molecular models, as proposed in this paper. The simulated isotherms and the isosteric heats, generated with the structural molecular models, agree very well with experimental data. Analyses of the microscopic mechanism of adsorption include local density distributions and snapshots of molecular configurations, and local order parameters were used to understand the packing of the adsorbate layer.