Dielectric and quasi-elastic neutron spectroscopy of monolayer water in a vermiculite clay

We report on results of quasi-elastic neutron scattering and dielectric spe ctroscopy of a mono-layer water confined between rigid platelets in the 2-d imensional structure of Na-vermiculite clay. The dynamics is very different from bulk water and also from the clay with two layers of water molecules in the interplatelet space. The only dynamics detected by, quasi-elastic ne utron scattering at room temperature is a planar rotation of water molecule s around the intercalated Na ions. The jump diffusion observed in bulk wate r and in the clay with two layers of water molecules in the interplatelet s pace is not observed in the monolayer system. At much lower temperatures (< 180 K) a broad but weak dielectric loss can be seen. It is attributed to r eorientation of water molecules assisted by the motion of intrinsic orienta tional defects.