Hill-type ultrasonic relaxation spectra of liquids
Abstract
The Hill relaxation spectral function, originally designed for the description of dielectric relaxation spectra, has been applied to a variety of sonic attenuation spectra. Both theoretical models and measured broadband spectra have been considered. It was found that the Hill function can be favorably used to represent the acoustic relaxation properties of critically demixing liquids but also of such liquid systems that show precritical behavior. The Hill spectral function also complies with the thermal and viscoelastic boundary effects in suspensions and emulsions, with the special absorption characteristics of surfactant solutions with high critical micelle concentration, and with effects of cluster formation in solutions of transition metal halides. Empirical relations between the relaxation time distribution parameters of the Hill function and characteristics of theoretical models are displayed.