INFLUENCE OF NANOSCALE POROSITY ON THE STRUCTURE AND DYNAMICS OF FLUIDS

Hydrocarbons, aqueous solutions, and gaseous species (e.g. CO2, CH4) can occupy the pores or fractures of numerous types of complex heterogeneous solids. The size, distribution and connectivity of these confined geometries, the chemistry of the solid, the chemistry of the fluids and their physical properties collectively dictate how fluids migrate into and through these micro- and nano-environments, wet and ultimately react with the solid surfaces. In order to assess key features of the fluid-matrix interaction at the nanoscale, a multidisciplinary approach was taken that employed neutron and X-ray scattering, simulations, and thermodynamic measurements to quantitatively describe the molecular properties of pure water, aqueous electrolytes and simple hydrocarbons confined to well-characterized porous media that serve as analogues to natural materials. Results have been obtained in four separate, but interrelated areas. Various types of microscopy (SEM; TEM) and scattering (SAXS, SANS) have been used to characterize a number of porous silicas, carbon fiber monoliths, zeolites and clays prior to interaction with fluids. Water adsorption/desoprtion isotherms have been determined on these materials up to 200oC. FTIR, NMR and QENS spectra have been obtained on water and, in the case of QENS, on electrolyte solutions (LiCl, CaCl2, NdCl3) confined in silica pore glass. Our simulation (GCMC) effort thus far has focused on the behavior of water in slit pores geometries composed of either carbon or mica. These studies conducted in concert are providing an understanding at the molecular level of how intrinsically different fluids behave in confined geometries compared to bulk systems. If properly calibrated and scaled, an atomistic or molecular understanding of fluid-solid interaction may provide quantitative insight into the behavior of systems at the macroscopic scale.