Liquids in confined geometry: How to connect changes in the structure factor to modifications of local order

The recent advances in the syntheses of mesostructured porous silicates (MCM-41 and SBA-15) allow us to study liquids confined in highly regular geometry. Hence, one might get to a better understanding of the structure and the dynamics of confined fluids. In this paper, we address the problem of the interpretation of the structure factor of a confined phase. Distortions due to geometric effects-so-called "excluded volume effects" and "cross-correlation terms"-may dominate the observed features and cannot be ignored. We present a generalization of the formalism introduced by Soper It is applied in the case of a honeycomb-type lattice of parallel cylindrical pores, which corresponds to the topology of these novel porous materials. It shows that the large variations of the experimental structure factor of confined liquid benzene at room temperature are essentially attributed to an "excluded volume effect" that does not reflect different local ordering of the confined phase. (C) 2003 American Institute of Physics.