Water Orientation in Smectites Using NMR Nutation Experiments

We observed the arrangement of water molecules when confined in the interlayer space of smectites using low field nutation experiments. Despite the presence of paramagnetic impurities that prevent such observation at high field, we can determine the amount of water in strong interaction with the clay surface, i.e., water molecules which are partially oriented within each platelet. The experiments do not require the orientation of the clay platelets relative to the magnetic field. We present the NMR theory, the signal processing, and the results on a series of 4 homoionic smectites (Na, Ca, Mg, and K) at different relative humidities in order to vary the water content and the basal spacing. In these systems, we found that between 0.5 and 2.5 water molecules per ion are oriented.