Soviet Physicists Cracked Sound's Strange Behavior in Viscous Liquids by Treating Them as Emulsions
Propagation of Sound in Strongly Viscous Liquids (1966) [pdf]
In 1966, Isakovich and Chaban showed that the standard relaxation theory fails for strongly viscous liquids like glycerine: absorption and velocity dispersion scale with the square root of frequency, not the expected power laws. They proposed that such liquids are microinhomogeneous, with ordered molecular inclusions in a disordered component, and that diffusion between the two restores equilibrium. The theory, using no free parameters, matched experiments across the dispersion region and even estimated that about six glycerine molecules span the ordered region at 22°C.
It has been found that quantitative agreement with experiment for the dispersion of sound velocity could be materially improved if it was assumed that the relaxation time is not constant for a given material at a given temperature but is proportional to the square root of the frequency.