Equilibrium behavior of fluids confined in amorphous microporous materials

This thesis is concerned with the relationship between the structure of amorphous microporous materials and fluids confined therein. For materials such as activated carbon and silica gel, whose microstructural properties are extremely sensitive to their history, it is important to recognize how changes in material properties will affect its performance in specific applications. Furthermore, this type of understanding aids in the tailoring of adsorbents with properties desirable for specific applications. We employ molecular simulation as a means to probe fluids in amorphous materials. We use the highly flexible Monte Carlo method, whose formalism can be adapted for application to a wide variety of problems. We apply this method particularly to studies on a model silica gel. In the first two studies, we focus on the properties of the adsorbed fluid in the context of changing adsorbent properties. We first probe the effect of physical confinement on the phase behavior of a binary liquid mixture that exhibits regions of immiscibility in the bulk. We next examine the influence of silica gel surface chemistry on the adsorptive behavior of polar fluids such as water. This work particularly focuses on the development of an adequate model to describe the adsorbent. Good qualitative agreement with experimental observations is achieved, both with respect to the energetic heterogeneity of the material and the response of water vapor to changes in the surface chemistry of the adsorbent. Finally, we focus on the effect of the molecular probe in the adsorption behavior in the same adsorbent. We study the adsorption of n-alkanes, which demonstrates that changing the chain length of the adsorbent leads to changes in adsorbate behavior when confined in similar micropores. The heats of immersion of such materials are also computed with good accuracy, a calculation which has not been previously attempted. This calculation can provide a useful contact between simulation and experiment when other data is lacking