Mutual Information in Molecular and Macromolecular Systems

Abstract

The relaxation properties of viscous liquids close to their glass transition (GT) have been widely characterised by the statistical tool of time correlation functions. However, the strong influence of ubiquitous non-linearities calls for new, alternative tools of analysis. In this respect, information theory-based observables and, more specifically, mutual information (MI) are gaining increasing interest. Here, we report on novel, deeper insight provided by MI-based analysis of molecular dynamics simulations of molecular and macromolecular glass-formers on two distinct aspects of transport and relaxation close to GT, namely dynamical heterogeneity (DH) and secondary Johari–Goldstein (JG) relaxation processes. In a model molecular liquid with significant DH, MI reveals two populations of particles organised in clusters having either filamentous or compact globular structures that exhibit different mobility and relaxation properties. In a model polymer melt, MI provides clearer evidence of JG secondary relaxation and sharper insight into its DH. It is found that both DH and MI between the orientation and the displacement of the bonds reach (local) maxima at the time scales of the primary and JG secondary relaxation. This suggests that, in (macro)molecular systems, the mechanistic explanation of both DH and relaxation must involve rotation/translation coupling.

Analysis of Vibrational Spectra of Tetrafluoroethane Glasses Deposited by Physical Vapor Deposition

“…Amorphous glassy solids have recently become of particular interest. − Glasses are nonequilibrium, amorphous bodies that play a huge role in the current stage of technological development. Glass has no long-range order of atoms, like all materials with a non-crystalline structure.…”

Glass Transition and Related Phenomena

“…Papers [1][2][3][4], based on the results of computer simulations, constitute an interesting collection of successful applications of isotropic and anisotropic models in equilibrium and non-equilibrium molecular dynamics (MD) computations, which are even extended to the study of dynamic properties using artificial intelligence methods [4] that become unavoidably necessary research tools. Lagogianni and Varnik [1] studied metallic glasses and their deformations, called shear bands, that hamper the application of such glasses as structural components.…”

“…By performing and analyzing MD simulations of a molecular liquid consisting of flexible trimers and a model polymer melt, Leporini's group argued [3] that mutual information (MI) can be extracted on two distinct aspects of transport and relaxation near the glass transition, which are dynamic heterogeneity (DH) and secondary Johari-Goldstein (JG) relaxation processes. In the model molecular liquid with significant DH, the MI-based analysis revealed two different fractions, which were spatially grouped in clusters that exhibited different mobility and relaxation properties.…”