Interfacial Properties of Carbon Dioxide–Water–Silica from Expanded Ensemble Monte Carlo Simulations
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This dissertation demonstrates the use of expanded ensemble Monte Carlo simulations to compute the bulk phase coexistence conditions of CO2–H2O mixtures and the interfacial properties of these mixtures over model silica surfaces. The dissertation begins by recounting previous measurements in the literature of the CO2–H2O interfacial tension and CO2–H2O–mineral contact angles at conditions relevant to CO2 geological sequestration. It then describes the expanded ensemble Monte Carlo simulation framework for computing bulk and interfacial properties. Next, this framework is applied to a simple model: a series of binary symmetric Lennard-Jones mixtures. Each mixture is found to remain in the partial wetting regime throughout the range of temperatures studied. The simulation framework is then applied to bulk CO2–H2O mixtures at high temperature (523 K) and low temperature (323 K), and the CO2 mole fractions in both the CO2-rich and H2O-rich phases compare favorably with simulations from the literature. Finally, the results of expanded ensemble simulations of CO2–H2O–silica are presented for two classes of silica models. The interfacial tensions are found to agree with previous simulations and experiments, and the CO2–H2O–silica contact angles for sufficiently hydrophilic surfaces at 323 K are found to agree with reputable experiments. Overall, this dissertation demonstrates that expanded ensemble Monte Carlo simulation methods may be used to study model CO2–H2O–silica systems at geological sequestration conditions.