NMR Doublet Splitting in Aqueous Montmorillonite Gels

Abstract

Doublet splitting in the NMR spectrum of montmorillonite clay–water systems arises from the preferred orientation of water molecules on clay gels. The small magnitude of the doublet splitting compared to that expected for motionless molecules indicates dynamic preferential orientation of the water in the clay–water systems. The fact that the doublet splitting is observed for the D₂O–clay gels at all temperatures but only for the H₂O–clay gels at low temperatures and relatively small water content suggests the importance of hydrogen exchange in the observation of the H₂O doublet. Hydrogen exchange “washes out” the proton doublet but not the deuteron doublet. The reason for this is the difference in the proton and deuteron nuclear spin interactions which give rise to the doublet.