Determining the Root-Mean-Square Amplitude of the Shear Modulus in Salol by the Inelastic Light Scattering Method

Abstract—The presence of the medium-range order in the glassy materials, i.e. structural correlations at the nanometer scales, leads to fluctuations of elastic constants with the same characteristic radius of correlations. The problem concerning the characteristic amplitude of these fluctuations is of great interest from both the application point of view and that of fundamental understanding of the structure and dynamics of glassy materials. In this work, the value of the nano-scale root-mean-square fluctuations of the shear modulus in the molecular glass salol (phenylsalicylate) and its dependence on temperature in the process of glass melting to a supercooled liquid are found. With this purpose, the theory of elasticity in the medium with spatial fluctuations of elastic constants is used when calculating the free path of phonons, according to perturbation theory. In addition, in the supercooled state of material, the contribution of the structure relaxation to phonon attenuation is considered. By using the Ioffe–Regel criterion for localization of transverse phonons, the relationship between the value of the shear modulus fluctuations and the frequency of the so-called boson peak induced by them in the spectrum of the vibrational excitations of glasses is found. This frequency is determined from the experimental data on the spectra of low-frequency inelastic light scattering in salol. Comparison with the theory makes it possible to find the temperature dependence of the value of nanoscale root-mean-square fluctuations of the shear modulus. In addition, this dependence is compared with the temperature behavior of the Landau–Placzek parameter in salol. The temperature dependence of the radius of structural correlations in salol and glycerine is also determined and compared with the temperature dependence of the size of the dynamic inhomogeneity.