2 H NMR spectroscopy was used to detect the influence of confinement on the structural and dynamical properties of water molecules adsorbed in the interlamellar space of a natural clay (Montmorillonite) within partially hydrated self-supporting films. Multiscale numerical modeling (Monte Carlo simulations, molecular dynamics, and Brownian dynamics) was used to quantify the importance of the various relaxation mechanisms likely to be responsible for the NMR relaxation of the water molecules within such complex environment. Because of the significant fraction of iron present in these natural clays, the large value of the transverse relaxation rate measured for the confined water molecules is compatible with a dominant paramagnetic coupling modulated by the long-range diffusion of water molecules. Finally, the angular variation of the apparent relaxation rate can be used to extract the distribution of the directors of the clay lamellae within the selfsupporting film.

H spin-locking relaxation measurements were used to probe the dynamical properties of water molecules confined between individual montmorillonite lamellae within dense clay sediments. Because of the significant amount of structural iron in these natural clays, the dipolar paramagnetic coupling is the major mechanism responsible for the relaxation of these confined water molecules. By calculating the time evolution of the various coherences of spin 1 nuclei under the irradiation pulse implied in these spin-locking relaxation measurements, we illustrate how the paramagnetic coupling largely extends the dynamical range usually investigated by such relaxation measurements. We exploit that property to compare the water mobility predicted, at a reduced time scale, by molecular dynamics simulations with the average residence time of the water molecules inside the clay interlayer.

With the use of 23 Na nuclear magnetic resonance spectroscopy and 1 H pulsed field gradient attenuation, we have determined the critical concentration at which the isotrope/nematic transition occurs within aqueous dispersions of synthetic Laponite clay used as a model of a charged anisotropic colloid. The dense macroscopic clay samples were prepared by oedometric compression, leading to a critical concentration for the isotrope/ nematic transition significantly higher than that determined previously by using birefringence detection within capillary tubes. The increase of the nematic ordering detected by NMR as a function of the clay concentration is more progressive than the sharp ordering predicted by numerical simulations of the isotrope/nematic transition of rigid disks. This difference may result from some size and shape heterogeneities of the Laponite clay samples or from the competition between the relative orientation of the particles induced by the excluded volume and the electrostatic interactions.

Aqueous dispersions of Laponite, a synthetic clay neutralized by sodium counterions, are used as a model of charged anisotropic colloids to probe the influence of the shape of the particle on their organization within a macroscopic nematic phase. Because of the large fraction of condensed sodium counterions in the vicinity of the clay particle, (23)Na NMR is a sensitive probe of the nematic ordering of the clay dispersions. We used line shape analysis of the (23)Na NMR spectra and measurements of the Hahn echo attenuation to quantify the degree of alignment of the individual clay particles along a single nematic director. As justified by simple dynamical simulations of the interplay between the sodium quadrupolar relaxation and its diffusion through the porous network limited by the surface of the clay particles, we probe the degree of ordering within these clay nematic dispersions by measuring the variation of the apparent (23)Na NMR relaxation rates as a function of the macroscopic orientation of the clay dispersion within the magnetic field.