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Acoustic excitations in topologically disordered media at mesoscale presentanomalous features with respect to the Debye's theory. In a three-dimensionalmedium an acoustic excitation is characterized by its phase velocity, intensityand polarization. The so-called Rayleigh anomalies, which manifest inattenuation and retardation of the acoustic excitations, affect the first twoproperties. The topological disorder is, however, expected to influence alsothe third one. Acoustic excitations with a well-defined polarization in thecontinuum limit present indeed a so-called mixing of polarizations atnanoscale, as attested by experimental observations and Molecular Dynamicssimulations. We provide a comprehensive experimental characterization ofacoustic dynamics properties of a selected glass, 1-octyl-3-methylimidazoliumchloride glass, whose heterogeneous structure at nanoscale is well-assessed.Distinctive features, which can be related to the occurrence of the Rayleighanomalies and of the mixing of polarizations are observed. We develop, in theframework of the Random Media Theory, an analytical model that allows aquantitative description of all the Rayleigh anomalies and the mixing ofpolarizations. Contrast between theoretical and experimental features for theselected glass reveals an excellent agreement. The quantitative theoreticalapproach permits thus to demonstrate how the mixing of polarizations generatesdistinctive feature in the dynamic structure factor of glasses and tounambiguously identify them. The robustness of the proposed theoreticalapproach is validated by its ability to describe as well transverse acousticdynamics.

Rayleigh anomalies and disorder-induced mixing of polarizations at nanoscale in amorphous solids. Testing 1-octyl-3-methylimidazolium chloride glass