LIQUID FRAGILITY AND THE GLASS-TRANSITION IN WATER AND AQUEOUS-SOLUTIONS

Various properties of water and aqueous solutions are reviewed within the framework of the 'strong/fragile liquids' classification. The pecu liar situation presented by pure water and dilute aqueous solutions, i s discussed, then the more concentrated and easily glass-forming solut ions involving salts, molecular components, and polymeric components a re reviewed. In the electrolyte cases the properties of solutions in t he glass-forming domain up to the ice-saturated limit prove to be thos e of very fragile liquids. This behavior is incompatible with the prop erties of pure water near the glass transition of vitreous ice (amorph ous solid waters; ASW), supporting the notion that the latter is a dis tinct and separate phase of H2O. In the molecular solute cases, partic ularly with sugar components, the liquids appear to become stronger wi th increasing water content, whereas with water-plasticized polymers t he position is not yet clear. Evidence on methacrylate polymers and pr oteins suggested that they may be rather strong. With this background the effects of solution fragility on the kinetics of longer time scale processes is discussed In particular, the freezing of chemical reacti ons at temperatures well above T(g) is considered in relation to the f luid (solvent) fragility and accounted for in terms of a simple diffus ion model.