Steven Strong

Supercritical fluids have wide-ranging applications from hazardous waste cleanup to decaffeination. The diversity of applications of supercritical fluids comes from their principal physical property: tunable density. Below the critical point, only small areas of the density-temperature phase diagram are accessible, because the density is discontinuous across the liquid-gas phase transition. Above the critical point, the density can be tuned continuously, and with it, many other important physical properties. For example, one can optimize a supercritical fluid for applications in industrial extraction processes like decaffeination by tuning the density to simultaneously give liquid-like solvation properties and a low, gas-like viscosity. The structure and dynamics of supercritical fluids at a molecular level, however, are poorly understood, especially in nontrivial fluids like water, where hydrogen bond networks dominate the liquid state. We use computer simulations to understand how the behavior of these fluids on the molecular scale controls their macroscopic properties. This approach not only deepens our current understanding of the properties of supercritical fluids, but also paves the way to new applications.