Study of Water Layers Adsorbed on Na‐ and Ca‐Montmorillonite by the Pulsed Nuclear Magnetic Resonance Technique

Abstract

The pulsed magnetic resonance technique was applied to the measurement of the longitudinal (T1) and transversal (T2) relaxation time of water molecules adsorbed by Na‐ and Ca‐Montmorillonite, In the Na‐clay the water was adsorbed as a monomolecular layer whilst in the Ca‐clay, the bimolecular layer was formed under specified water vapor pressures. The effect of paramagnetic centers (Fe3+) was corrected and the samples were studied between + 30°C and −80°C. The main contribution to T1 was the “inter” contribution of protons diffusing from one water molecule to another whilst T2 results from simultaneous rotational (intramolecular) and diffusional (intermolecular) contributions. The proton diffusion coefficient and the life‐time of a proton on one specified water molecule is derived from T1 inter. The calculated value at 298°C is equal to 10−7 times the life‐time in liquid water, suggesting a dissociation degree 107 times higher in the adsorbed state than in liquid water. This increase in the dissociation degree as well as the reported activation energies are in good agreement with experimental data obtained from conductimetric and dielectric measurements performed previously.

Hydrogen bonding and polywater in clay-water systems

“…analysis, consists of a negatively charged, planar, hexagonal network of water molecules that is held together by protons or hydronium ions. NMR and other investigations of water in clays indicate that the water molecules are oriented parallel to the planar clay surfaces Snowden, 1969a, 1969b) and that proton dissociation is much higher than that in normal water (Ducros and Dupont, 1962;Mortland et al, 1963;Touillaux et al, 1968). Thus, the orientation and dissociation of water in clays are consistent with the proposed structure of polywater.…”

Metachromasy in clay-dye systems: the adsorption of acridine orange by Na-saponite

“…4). Interlayer water has been reported to be much more acidic than bulk liquid water (Touillaux et al, 1968;Yariv, 1992) and the shift of band at to longer wavelengths is due to high acidity of the environment in which the dye resides (Robinson, 1994).…”

An Ultraviolet Spectroscopic Method for Monitoring Surface Acidity of Clay Minerals under Varying Water Content

“…Acidic behavior is inferred from the physical nature of the source. For example, Brdnsted acidity is inferred from protonic behavior as reflected by infrared spectroscopy (Uytterhoeven et al, 1965), n.m.r, spectroscopy (Trouillaux et al, 1968), or conductometric measurements (Fripiat et al, 1965).…”