Multiscale Approach to the Structural Study of Water Confined in MCM41

Abstract

We present a protocol for simultaneous structural characterization of aconfined fluid and the confining Substrate, along with the extractionof site-site pair correlation functions of the liquid of interest. Thisis based on neutron diffraction experiments, exploiting where feasiblethe isotopic substitution technique, analyzed through numerical coarsegraining calculations and atomistic simulations. All of the subtletiesof the experimental procedure, the needed ancillary measurements, andthe recipe for tailoring the numerical codes to the real experiment andsample are described in the case of water confined in MCM41-S-15. Inparticular the excluded volume effects and the relevance ofliquid-Substrate cross-correlation terms in the neutron cross sectionare quantitatively discussed. The results obtained for the microscopicstructure of water evidence a non-homogeneous distribution of moleculeswithin the pore, with the presence of water-substrate hydrogen bonds,and a strong distortion of the water-water radial distributionfunctions with respect to those of bulk water extending at least up tothree hydration layers.