Nature of Molecular Rotation in Supercooled Glycerol under Nanoconfinement

The dynamics of glass-forming liquids under nanoconfinement is key to understanding a variety of phenomena in nature and modern technology. We report a C-13 NMR spectroscopic Study that directly demonstrates that a-relaxation in bulk glycerol involves an isotropic rotational jump of the constituent molecules. The activation energy of this motion is similar to 78 kJ mol(-1) in the bulk, which abruptly changes to a low value of similar to 27.5 kJ mol(-1), characteristic of beta-processes, upon confinement of glycerol into similar to 2 nm pores in mesoporous Silica. This observation implies that the molecular dynamics associated with Structural relaxation near glass transition are inherently different in supercooled glycerol in the bulk and under extreme nanoconfinement.