Molecular dynamics analyzed in terms of continuous measures of dynamic heterogeneity

Molecular mobility and the glass transition in amorphous glucose, maltose, and maltotriose

“…23 The stretched-exponential decay function is thought to provide an appropriate kinetic model for the description of rate processes in hierarchically structured amorphous materials. [27][28][29][30][31][32][33] Analysis of the temperature dependence of the lifetime indicates that the rate constant for intersystem crossing to the ground state (k TS0 ) is sensitive to the physical state of the amorphous matrix. The magnitude of k TS0 , the collisional quenching constant, is sensitive to internal factors related to vibrational coupling between the excited T 1 state and the S 0 ground state 34 as well as external factors related to dissipation of the vibrational energy of the excited probe into the surrounding matrix.…”

Erythrosin B Phosphorescence Monitors Molecular Mobility and Dynamic Site Heterogeneity in Amorphous Sucrose

“…All intensity decays at all temperatures were satisfactorily fit using a stretched exponential decay model in which the lifetime (t) and the stretching exponent (b) were the physically meaningful parameters. Although we reported previously that erythrosin phosphorescence exhibits two lifetimes in a fractured sucrose powder (Shah and Ludescher, 1995), we used a stretched exponential decay model here for several reasons: 1), the stretched exponential model provides a statistically reasonable fit to all measured decays; 2), it provides a simple and tractable way of describing potentially complex decay transients using only two adjustable parameters, t and b; 3), there are sound theoretical reasons for supposing that rate constants for kinetic processes within an amorphous solid are distributed in a manner appropriate for description by a stretched exponential (Richert, 1997(Richert, , 1998(Richert, , 2000; and 4), a number of empirical studies have demonstrated the applicability of the stretched exponential model for describing luminescence decays within amorphous solids (Hofstraat et al, 1996;Linnros et al, 1999;Jaba et al, 2000;Pophristic et al, 2000). In this study we use such an analysis as an effective and efficient description of the decay kinetics that captures both the rates (t) and the heterogeneity (b) inherent within the decay processes.…”

Heterophase liquid states: Thermodynamics, structure, dynamics

“…In Bernal's mechanical model of the dense random packing of hard spheres, six types of the local order (Bernal's holes) are statistically significant and nearly one third of them are non-crystalline [13]. Similar results are obtained using computer simulations of liquids and glasses with different interatomic potentials [14-18] 2 .A wide spectrum of relaxation times in glass-forming liquids is observed due to the variety of SRO types (see [19,20] and references cited).Since SRO is the molecular order formed due to microscopic forces, the correlation length ξ SRO is equal to or exceeds the range of direct molecular interactions. Therefore, to describe heterophase states, a mesoscopic theory is needed, in which molecular species of size r ∼ ξ SRO specified by SRO are "elementary" structural elements rather than molecules.…”

“…Thermally activated cooperative structural rearrangements which can involve up to ∼ 10 2 molecules [19,20,[63][64][65][66][67] are called α-relaxation. A large amount of the molecules are involved in the rearrangement due to correlations.…”