Induced thermal dynamics in the melt of glycerol and aerosil dispersions

A high-resolution calorimetric spectroscopy study has been performed on pure glycerol and colloidal dispersions of an aerosil gel in glycerol covering a wide range of temperatures from 300 to 380 K, deep in the liquid phase of glycerol. The colloidal glycerol+aerosil samples with 0.07, 0.14, and 0.32 g of silica per cm3 of glycerol reveal activated energy (thermal) dynamics at temperatures well above the Tg of the pure glycerol. The onset of these dynamics appears to be due to the frustration or pinning imposed by the silica gel on the glycerol liquid and is apparently a long-range, cooperative phenomena. Since this behavior begins to manifest itself at relatively low silica densities (large mean void length compared to the size of a glycerol molecule) and speeds up with increasing density, these induced dynamics are likely due to a coupling between the flexible aerosil gel and large groups of glycerol molecules mediated by mutual hydrogen bonding. This is supported by the lack of such thermal dynamics in pure aerosil gels, pure glycerol, or aerosil gels dispersed in a non-glass-forming, non-hydrogen-bonding, liquid crystal under nearly identical experimental conditions. The study of such frustrated colloids may provide a unique avenue for illuminating the physics of glasses.