Ultraslow relaxation of hydrogen-bonded dynamic clusters in glass-forming aqueous glucose solutions: A light scattering study.

We report static and dynamic light-scattering measurements of aqueous glucose solutions near their glass transition. Photon correlation spectroscopy reveals two relaxation processes present in the supercooled liquid: a nonexponential and nonhydrodynamic, alpha -relaxation occurring at short times and an exponential and hydrodynamic relaxation occurring at longer times. The slow relaxation is seen only in the polarized scattering geometry and is in many ways identical to the "ultraslow" mode recently observed by others in specially annealed molecular glass-forming liquids and attributed to the formation of long-range density correlations or "dynamic clusters." Static light scattering confirms the existence of excess scattering in our glucose solutions that is consistent with clusters in a size range between 30 and 60nm . The size of the clusters varies with the water content and the clustering appears to be associated with the percolation of a hydrogen-bonded glucose network.