Student Theses and Dissertations

Date of Award


Document Type


RU Laboratory

Cohen EGD Laboratory


In this thesis I am concerned with the dynamical properties, at the molecular level, of binary fluid mixtures in equilibrium; binary fluid mixtures are fluids consisting of two different components. As for simple (one component) fluids, the main experimental probes for the study of these properties of binary mixtures are light and neutron scattering. To connect the dynamics with scattering experiments one can use the kinetic theory of fluids. I have applied the kinetic theory to binary mixtures where the atomic masses of the molecules of the two components are very different (disparate-mass binary mixtures). I have studied both dilute (gaseous) mixtures and dense mixtures. In the description of the dynamics of the fluid through the densitydensity correlation functions, one can introduce modes, which can be thought of as the different channels by which the correlations decay in time. Some modes are propagating, in the sense that they describe propagating, and damped, processes. Others are not propagating, and describe diffusive, purely damped processes. The results concern the appearance of a fast propagating mode, in disparate-mass binary mixtures, in a vast range of densities, from dilute gas mixtures to rather high (liquid) densities. This fast mode appears beyond the hydrodynamic regime. One can call this mode fast sound, because, like ordinary sound, it propagates, but it is faster. The most important point is that the fast sound is associated with the dynamics of the light component only. In the thesis I explain how this phenomenon could be observed in light and neutron scattering experiments. If it is detected in actual scattering experiments on disparate-mass binary mixtures it would be the first time that a non hydrodynamic mode in a fluid is clearly "seen".


A thesis submitted to the Faculty of The Rockefeller University in partial fulfillment of the requirements for the degree of Doctor of Philosophy

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