Rederivation and Analysis of Fixman's Theory of Excess Sound Absorption near Fluid Critical Points

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Abstract
We retrace the thermodynamic and hydrodynamic analysis used by M. Fixman [J. Chem. Phys. 36, 1961 (1962)] in the first quantitative explanation of the anomalously large sound absorption near fluid critical points. With some oversights and ambiguities corrected, the basis theory is seen to be firmly based in classical thermodynamics and hydrodynamics. The use of the Ornstein—Zernike, Debye, and Flory—Huggins models for reduction of key quantities appears necessary for thermodynamic consistency. For analysis of experimental data, Fixman's theory is preferred over alternative theories, though no one theory is truly satisfactory. With a view toward interpreting our data presented in the following paper [V. P. Gutschick and C. J. Pings, J. Chem. Phys. 55, 3845 (1971)], we argue the applicability of Fixman theory in systems having a strong background of additional (thermal) relaxation.