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

Abstract
We report on results of quasi-elastic neutron scattering and dielectric spectroscopy of a mono-layer water confined between rigid platelets in the 2-dimensional 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 neutron scattering at room temperature is a planar rotation of water molecules around the intercalated Na ions. The jump diffusion observed in bulk water and in the clay with two layers of water molecules in the interplatelet space 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 reorientation of water molecules assisted by the motion of intrinsic orientational defects.