The behavior of thermodynamic properties of fluids and fluid mixtures is strongly affected by the presence of critical points, such as the vapor-liquid critical point in one-component fluids, plait points and consolute points in liquid mixtures, etc. Associated with critical phase-transition phenomena is the presence of long-range fluctuations. Based on modern theoretical approaches we are trying to obtain an accurate representation of the thermodynamic behavior of fluids and fluid mixtures close to and not so close to these critical points. The aim is to obtain fundamental equations for chemical engineering applications over large ranges of temperatures and densities that incorporate the crossover from singular critical thermodynamic behavior to regular thermodynamic behavior far away from critical phase transitions. Some of the research is pursued in collaboration with scientists and chemical engineers at the National Institute of Standards and Technology.
Transport Properties of Fluids and Fluid Mixtures
The presence of long-range fluctuations in fluids and fluid mixtures near critical-point phase transitions also strongly affects the behavior of transport properties. The effects of long-range fluctuations on the transport properties can be understood quantitatively with the methods of generalized hydrodynamics. The aim is to obtain accurate representations of the transport properties of fluids and fluid mixtures over a large range of temperatures and densities consistent with the thermodynamic behavior discussed above. In addition, an experimental program is pursued for measuring transport properties, like viscosity and Soret coefficients, of fluids and fluid mixtures.
Fluctuations in Nonequilibrium Fluids
There exists currently considerable interest in the nature of fluctuations in fluids and fluid mixtures driven far away from equilibrium either by imposing a temperature gradient or by imposing a shear rate. An interesting feature is that under such nonequilibrium conditions all fluctuations become long range even when the system is far away from a critical-point phase transition. Little actual experimental information is available and we are studying these fluctuations by observing the static and dynamic properties of laser light scattered from such fluids out of thermal equilibrium. Optical experiments for studying mass diffusion and chemical diffusion processes in fluid mixtures are being pursued