The glass transition and relaxation behavior of bulk water and a possible relation to confined water

Artikel i vetenskaplig tidskrift, 2010

Due to the widespread importance of water and the difficulty to study it in the so-called no man's land between 150 and 235 K, deeply supercooled bulk water is currently heavily debated. It speculates about its properties from extrapolations of experimental data on bulk water above 235 K and below 150 K, computer simulations, and experiments on confined water for which the finite size effects may prevent crystallization in the no man's land. However, it is far from obvious how experimental data on bulk water should be extrapolated to the temperature range of the no man's land or how relevant results from computer simulations and studies of confined water are for bulk water. In this paper the structural and dynamical properties of supercooled bulk water are tried to be understood from experimental results on confined water and comparisons with bulk water. We propose that a similar crossover from a high temperature alpha-relaxation to a low temperature beta-relaxation occurs also for bulk water but at a higher temperature than for confined water due to the larger average number of hydrogen bonds between the water molecules in bulk water. In the case of bulk water the crossover is expected to occur around the critical temperature T-s approximate to 228 K when the buildup of an icelike tetrahedral network structure is completed. The proposed interpretation is the simplest one that is able to explain many of the peculiar properties of supercooled water.