A Brillouin light-scattering investigation of the glass-transition in low molecular weight network glass-formers

Order-Determined Structural and Energy Transport Dynamics in Solid-Supported Interfacial Methanol

Energy transport dynamics in different nanostructures are crucial to both a fundamental understanding of and practical applications for heat management at the nanoscale. It has been reported that thermal conductivity may be severely impacted by stacking disorder in layered materials. Here, using ultrafast electron diffraction in the reflection geometry for direct probing of structural dynamics, we report a fundamental behavioral difference due to stacking order in an entirely different system-solid-supported methanol assemblies whose layered structures may resemble those of two-dimensional (2D) and van der Waals (vdW) solids but with much weaker in-plane hydrogen bonds. Thermal diffusion is found to be the transport mechanism across 2D-layered films without a cross-plane stacking order. In stark contrast, much faster ballistic energy transport is observed in 3D-ordered crystalline solids. The major change in such dynamical behavior may be associated with the efficiency of vibrational coupling between vdW-interacted methanol layers, which demonstrates a strong structure-property relation.

Density dependence of dynamical heterogeneity in fluid methanol

Brillouin and Raman scattering experiments on methanol through its glass transition under pressure are reported. The Brillouin scattering data were analyzed using viscoelastic theory and a fit to the Vinet equation of state. The variation in the linewidth of the longitudinal acoustic mode with pressure shows a broad maximum centered around 3 GPa. The pressure evolution of the relaxation time in the GHz range is obtained, and the Raman data are analyzed in terms of the Boson peak and its associated relaxation time in the THz range. The pressure evolution of these two relaxation processes extends previous determinations of relaxations at lower frequency based on dielectric measurements in supercooled methanol. The relaxation processes in glass-forming methanol have now been investigated over a wide frequency range and their evolution followed over a large variation of density.