Fluid structure near heterogeneous surfaces

Surface heterogeneity, geometric or energetic, can arise in various circums tances, e.g,, surface defects, porous adsorbents, surface of amorphous mate rials, etc. Much effort, both in theory and in simulations, has been devote d to study fluid absorption on perfect plane surfaces up to now, In contras t, many fundamental questions remain open concerning the effect of surface disorder on the structure and thermodynamic properties of adsorbates near h eterogeneous surfaces. In this work, we propose a simple model for heteroge neous surfaces which allows us to address some of these questions by carryi ng out Monte Carlo simulations. An interesting feature of this model is tha t the counterpart with a structureless plane surface can be defined precise ly for the model heterogeneous surface. Thus, meaningful comparison between the two cases can be made which have allowed us to clearly reveal the infl uence of surface heterogeneity on the fluid structure near rough surfaces. We also propose a simple approach which relates the fluid density profile n ear a heterogeneous surface to that near a plane surface through a distribu tion function characterizing the surface corrugation. Results in very good agreement with simulations have been obtained from this approach. (C) 1999 American Institute of Physics. [S0021-9606(99)52401-X].