On the evolution of the heat spike in the isosteric heat versus loading for argon adsorption on graphite-A new molecular model for graphite & reconciliation between experiment and computer simulation

We have carried out an extensive computer simulation of argon adsorption on graphite at temperatures in the range 40 K-100 K, using a new molecular model for graphite, and compared our simulation results with new high-resolution experimental data. The new model accounts for: (1) The energetic corrugation of the graphene surface. (2) The smaller collision diameter of the carbon atoms (0.28 nm) in the outermost graphene layer compared to 0.34 nm in the lower layers. (3) The increase in the interaction energy well depth between argon and the carbon atoms of the outermost layer. (4) The closer spacing between the first and second layers compared to that between the inner layers. The simulated adsorption isotherms and isosteric heats give an improved description of the experimental data, especially in capturing the low temperature transition from a 2D liquid to a solid-like adsorbate and subsequently to an incommensurate solid, and of the variation in these properties with respect to temperature. Analysis of the isosteric heat versus loading reveals details of the rearrangement of the adsorbed molecules during the layer transition. (C) 2017 Elsevier Ltd. All rights reserved.