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We report a detailed analysis of the dynamic structure factor of glassy sorbitol by using inelastic X-ray scattering and previously measured light scattering data [B. Ruta, G. Monaco, F. Scarponi, and D. Fioretto, Philos. Mag. 88, 3939 (2008)]. The thus obtained knowledge on the density-density fluctuations at both the mesoscopic and macroscopic length scale has been used to address two debated topics concerning the vibrational properties of glasses. The relation between the acoustic modes and the universal boson peak (BP) appearing in the vibrational density of states of glasses has been investigated, also in relation with some recent theoretical models. Moreover, the connection between the elastic properties of glasses and the slowing down of the structural relaxation process in supercooled liquids has been scrutinized. For what concerns the first issue, it is here shown that the wave vector dependence of the acoustic excitations can be used, in sorbitol, to quantitatively reproduce the shape of the boson peak, supporting the relation between BP and acoustic modes. For what concerns the second issue, a proper study of elasticity over a wide spatial range is shown to be fundamental in order to investigate the relation between elastic properties and the slowing down of the dynamics in the corresponding supercooled liquid phase. [ABSTRACT FROM AUTHOR]

The dynamics of liquid sulphur have been investigated in the temperature region corresponding to the so-called λ transition by means of Brillouin light scattering. Results of this work, together with ultrasonic spectroscopy and inelastic X-ray scattering results in literature, indicate that the main structural relaxation is slightly affected by the transition and suggest that the dramatic increase of shear viscosity is related to the onset of a low-frequency additional relaxation. Such a feature is commonly found in rubber-like materials and can be related to the polymerization of sulphur molecules across the transition. [ABSTRACT FROM AUTHOR]

Brillouin light and X-ray scattering have been used to investigate the dynamic structure factor of supercooled and glassy m-toluidine in the temperature range 34-303 K. In addition to the ubiquitous α-relaxation, evidence is given of a fast relaxation process active in the ns-ps time region. Data on activation energy of the fast process are obtained from the attenuation of longitudinal acoustic modes. [ABSTRACT FROM AUTHOR]

Abstract: We present here a study of the acoustic dynamics of polymeric glassy sulfur. The data have been collected in the GHz frequency range by means of Brillouin light scattering for different scattering geometries. The choice of the experimental setup allows us to obtain information on the refractive index, n, that comes out to be close to that corresponding to the high temperature polymeric liquid phase. The longitudinal acoustic excitations have been investigated as a function of temperature from deep into the glassy state up to the glass transition temperature. The temperature dependence of the sound velocity is compared to the one measured in the liquid phase. We find that the sound velocity of the glass can be linearly extrapolated from that of the polymeric liquid measured in the THz frequency range with inelastic X-ray scattering. [ABSTRACT FROM AUTHOR]