Induced thermal dynamics in the melt of glycerol and aerosil dispersions

Dipti Sharma, Germano S. Iannacchione
2007 Journal of Chemical Physics  
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 cm 3 of glycerol reveal activated energy ͑thermal͒ dynamics at temperatures well above the T g of the pure glycerol. The onset of these dynamics appears to be due to the
more » ... e 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 molecule͒ 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. Downloaded 11 Apr 2007 to Redistribution subject to AIP license or copyright, see 094503-5 Induced thermal dynamics J. Chem. Phys. 126, 094503 ͑2007͒ Downloaded 11 Apr 2007 to Redistribution subject to AIP license or copyright, see Љ ͑open circles, left axis͒ and activation energy ⌬E ͑filled squares, right axis͒ of samples containing 0%, 5%, 10%, and 20% silica by mass.
doi:10.1063/1.2539000 pmid:17362111 fatcat:q7vz3wckqbbu3i3d4tlttpdsjy