Molecular dynamics near the glass transition

Density Scaling and Dynamic Correlations in Viscous Liquids

“…An increasingly non-Arrhenius behavior is thus associated with a slowing of the growth of dynamic correlations. This ostensible disconnect between dynamic heterogeneity and the distribution of relaxation times has been seen previously in o-terphenyl [47], tris(naphthyl)benzene [48,49,50], and sucrose benzoate [51], for which β is unchanged with temperature variations over the range of T/T g from ca. 1.22 to 1.02.…”

Why the glass transition problem remains unsolved?

“…However, Richert et al [27] recently reported that the dielectric spectra of trisnaphthylbenzene (TNB) are characterized by a temperature independent width (e.g. 1 À n d is constant and is equal to 0.50) from 345 to 417 K. The T g of TNB is 342 K. Photon correlation spectroscopic [44] and NMR [45] measurements all indicate a temperature independent distribution of relaxation times. Thus, the data of TNB contradicts the explanation based on spatial heterogeneities.…”

“…This is because the primitive relaxation times of all observables s 0l , uninfluenced by many-body relaxation dynamics, should have one and the same temperature dependence. Although the value of n g for viscosity is known from shear mechanical measurement [41] or light scattering data (n = 0.45) [44], n d for dielectric relaxation [26,27] and NMR [26,45] is 0.50, n D for self-diffusion is not yet available from experiment. Nevertheless, theoretical arguments have been given before to show that n g is larger than n D [46], and the explanation of the breakdown of the SE and DSE relations follows from this relation.…”

An explanation of the differences in diffusivity of the components of the metallic glass Pd43Cu27Ni10P20

“…The CM explanation was offered as an alternative explanation, but it was eclipsed by the popular and intuitively more appealing explanation that the difference in temperature dependence between diffusion and structural relaxation originates from the difference in how the respective observables averaged over the distribution of time scales of spatially heterogeneous dynamics [29][30][31]. However the premise of this popular explanation has been found to be contradicted by the temperature independence of the time or frequency dispersion of the structural relaxation of tri-naphthal benzene (TNB) [20,32,33], ortho-terphenyl (OTP) [21,22], sucrose benzoate [23], and indomethacin [24,36]. Thus the way to explain breakdown of SE relation from spatially heterogeneous dynamics is inconsistent with experiments, as concluded in a recent review ]40], although there is no doubt that the structural relaxation is dynamically heterogeneous.…”

“…Supported by various direct and indirect experimental evidences, there is no doubt that the structural relaxation is dynamically heterogeneous in most if not all glass-formers. However, the way it was used before to explain the difference in temperature dependence between diffusion and structural relaxation or viscosity is now recognized as inconsistent with experiments [20][21][22][23][24][30][31][32][33][34][35][36][37] and simulations [37][38][39]. The recent Perspective paper published by Ediger and Harrowell in the same journal [40] has made this amply clear by the statement: "Initially, it was suggested that the difference in temperature dependence between diffusion and structural relaxation, for example, arose as a result of the difference in how the respective observables averaged over the distribution of time scales.…”