Relaxation dynamics of perturbed water and other H-bonded liquids

Doktorsavhandling, 2010

Most liquids can be supercooled below its melting point where the dynamics dramatically slows down with decreasing temperature until the material appears solid on the experimental time scale and becomes stuck in an out-of-equilibrium configuration, a glass. Water, one of the most abundant substances on earth, is no exception. However the properties of supercooled water differ greatly from that of typical liquids and cannot be studied for temperatures between 150-235 K due to immediate crystallisation. This thesis concerns the dynamics of water, subject to perturbations, induced either by geometrical restriction of a host matrix or by non-water molecules in a mixture. These perturbations provide additional disorder and suppress crystallisation. By dielectric spectroscopy we investigate a suggested existence of a dynamic cross-over for structural relaxation of confined supercooled water. No such cross-over is found. We also study a dielectric process with unusual temperature dependence and provide a new, alternative interpretation. In addition, we investigate the effect of water in aqueous glass forming mixtures. Water has great implications to the dielectric properties, already for < 1% water content. With more water added, the glassy state is shown to exhibit a substantial dielectric relaxation related to a water specific process of local character, which does not control the viscosity of the liquid. The behaviour of this process is virtually independent on the properties of the structural relaxation in the supercooled state. Instead, it has a general behaviour for all investigated aqueous mixtures of low molecular weight. By quasielastic neutron scattering the probe the dynamics of the host molecules in aqueous mixtures and find anomalous behaviour also in the (stable) liquid state. Using the same technique, we also investigate the behaviour of other hydrogen bonded liquids in severe confinement.