NMR VISIBILITY AND ALKALI-TETRAALKYLAMMONIUM CATION COMPETITION IN LAPONITE SUSPENSIONS

Competition experiments between alkali counterions and tetraalkylammon ium cations for interaction with a clay (laponite) surface have been m onitored 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 spe ctra have been used to investigate the behaviors of the alkali cations , The variation in both Li-7 and Na-23 half bandwidths reflects the mo nolayer formation of tetraalkylammonium cations at the laponite surfac e. (C) 1996 Academic Press, Inc.