NMR visibility and alkali-tetraalkylammonium cation competition in laponite suspensions

Competition experiments between alkali counterions and tetraalkylammonium cations for interaction with a clay (laponite) surface have been monitored by Li-7 and Na-23 NMR. As a result of a stronger interaction of sodium cations, an increase of the Na-23 NMR visibility is observed with the addition of the organic salt. Multiple-quantum-coherence spectra have been used to investigate the behaviors of the alkali cations, The variation in both Li-7 and Na-23 half bandwidths reflects the monolayer formation of tetraalkylammonium cations at the laponite surface. (C) 1996 Academic Press, Inc.