| Gas-expanded liquids (GXLs) are a novel and environmentally benign class of solvent systems with applications in reactions, separations, nanotechnology, drug delivery, and microelectronics. GXLs are liquid mixtures consisting of an organic solvent combined with a benign gas, such as CO2, in the nearcritical regime. In general, liquid CO2 is a poor solvent whereas typical organics such as acetone and methanol are good solvents. The high compressibility of GXLs enables tunability of physicochemical properties of the liquid solvent, most notably gas solubility, polarity, and dielectric constant. To summarize, GXLs combine the excellent transport properties of supercritical fluids with the high solvation power of organic liquids.; Computer simulations are valuable tools for designing and optimizing environmentally-benign and cost-effective GXLs. Computer simulations can be used in tandem with experimental techniques to elucidate the local chemistry in a system. Knowledge of the local chemistry can then be used to manipulate bulk attributes such as reaction rates. In this work, simulations yielded relevant structural information in CO2-expanded methanol and CO 2-expanded acetone. The simulations demonstrated that addition of CO 2 resulted in clustering of methanol molecules in CO2-expanded methanol. Furthermore, Chapter 4 of this work shows that methanol molecules form hydrogen bonds with nitrogen-containing compounds, and these hydrogen-bonding interactions increase with CO2 pressure. Thus, the local solvation around molecules in CO2-expanded methanol can be manipulated with CO2 pressure. Likewise, Chapter 3 presents local compositions of organic around pyrene in CO2-expanded organic, and these local compositions are compared to the bulk compositions. Computer simulations can predict local compositions around a solute molecule needed to achieve a certain bulk reaction rate. Finally, Chapter 4 presents diffusion coefficients of nitrogen-containing compounds in CO2-expanded methanol obtained by both experiments and simulations. The diffusion coefficients increase with CO2 addition, demonstrating the enhanced transport in CO2 -expanded media. |
