Dynamics and glass transition of aqueous solutions of molecular liquid, polymer, and protein studied by broadband dielectric spectroscopy

Abstract

Broadband dielectric spectroscopy (BDS) is the most powerful tool for observing the dynamics of molecules in an extremely wide frequency range between 1 μHz and 50 GHz or more, i.e., the time window between megaseconds and picoseconds that covers the dynamics of solids to liquids. The progress of the investigations using BDS on the dynamics of aqueous solutions of hydrophilic molecular liquids, polymers, and proteins from solid to liquid states in this decade is presented in terms of the glass transition. The relaxation process, ν-relaxation, originating from the local reorientational motion of water molecules and the α-relaxation originating from the cooperative motion of hydrated solute are strongly related. The universalities of the dynamical hierarchy from fast and local motion of water molecules to slow and global cooperative motion of hydrated guest molecules extending over a wide range of glass transition temperature are successfully explained by applying the theoretical interpretation of mixtures of van der Waals liquids using the coupling model. More complicated partially crystallized aqueous protein solutions are also included.