Experimental support for a dynamic transition of confined water

We report neutron spin-echo (NSE) results of essentially two-dimensional water confined in a fully hydrated Na-vermiculite clay. The two layers of water molecules exhibit a broad distribution of relaxation times with a pronounced non-Arrhenius temperature dependence, typical for so-called fragile liquids, in the range 254-323 K. This high temperature behaviour is in contrast to an earlier dielectric study, where an Arrhenius dependence was observed for T < 215 K. The apparently contradictory NSE and dielectric results can be explained in terms of a 'fragile-strong transition somewhere in the temperature range 215-254 K.