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.

We have studied the self-diffusion properties of butyl-methyl-imidazolium bis(trifluoromethylsulfonyl)-imide ([BMIM][TFSI]) + water system. The self-diffusion coefficients of cations, anions, and water molecules were determined by pulsed field gradient NMR. These measures were performed with increased water quantity up to saturation (from 0.3 to 30 mol %). Unexpected variations have been observed. The self-diffusion coefficient of every species increases with the quantity of water but not in the same order of magnitude. Whereas very similar evolutions are observed for the anion and cation, the increase is 25 times greater for water molecules. We interpret our data by the existence of phase separation at microscopic scale.

The structural and dynamical properties of water molecules confined within dense clay sediment are investigated by 2H NMR spectroscopy and multiquanta relaxometry. The relative contribution of both quadrupolar and paramagnetic NMR relaxation mechanisms is evaluated by carefully analyzing the variation of 2H multiquanta NMR relaxation rates as a function of the orientation of the clay sediment within the static magnetic field. The same analysis is successfully applied to 2H multiquanta NMR spin-locking relaxation measurements, significantly increasing the probed dynamical range. That procedure leads to an accurate determination of the average residence time of the water molecule confined within the interlamellar space of the clay lamellae.

We have used a multiscale statistical analysis to interpret the mobility of water molecules diffusing within nematic aqueous dispersions of charged anisotropic nanocomposites (synthetic Laponite clays). The nematic ordering of dense aqueous suspensions (29-52% w/w) prepared by uniaxial compression is detected by analyzing the splitting of the nuclear magnetic resonance line of the quadrupolar counterions ( 7 Li and 23 Na) neutralizing the negative charges of the clay. The tensor describing the water self-diffusion is measured by 1 H pulsed gradient spin-echo (PGSE) NMR spectroscopy. It exhibits a large anisotropy of water mobility in these nematic dispersions. The macroscopic mobility of the water molecules is obtained from numerical simulations of Brownian dynamics (BD), by integrating the water trajectories over a time scale of 1 µs. The local mobility of the water molecules in the vicinity of the surface of the Laponite particles is deduced from preliminary molecular dynamics (MD) simulations of the trajectories of the water molecules confined between two clay fragments by integrating their trajectories over a time scale of a few picoseconds. The equilibrium density and initial configuration of these confined water molecules are deduced from grand canonical Monte Carlo (GCMC) simulations, by using a new clay/water force field determined from semi-empirical periodic (MINDO) quantum calculations coupled to perturbation theory for dispersion forces. This multiscale statistical analysis of the water mobility bridges the gap between the time scale (nanoseconds) accessible by MD simulations and the time scale (microseconds) accessible by BD, leading to macroscopic behavior comparable with experimental data. (I) IntroductionClays are charged anisotropic colloids used in many industrial applications (waste management and storage, heterogeneous catalysis, drilling, ionic exchange, etc.) exploiting their various physico-chemical properties (large affinity for water molecules and polar solvents, high specific surface and surface charge density, gelling, thixotropy, surface acidity, etc.). By contrast with natural clays which contains numerous impurities, Laponite is a synthetic clay frequently used for scientific investigations 1-13 because of its high chemical purity. Thus we have used this synthetic clay in order to validate our experimental procedures before investigating the behavior of the natural clay materials which are used for the industrial applications. Laponite clay results from the sandwiching of one layer of magnesium oxides, with an octahedral geometry, between two layers of silicium oxides, with an tetrahedral geometry. In dilute aqueous regime, Laponite clays behave as isolated rigid disks (diameter, 200-300 Å; thickness, 10 Å; and density, 2.7). 8,14,15 Because of the substitution of some Mg 2+ cations from their octahedral network by Li + cations, each Laponite disk bears about a thousand of negative electric charges neutralized by hydrated sodium counterions.The purpose of this study is to determine t...

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.

The purpose of this work was to understand how fractal dimension of two-dimensional (2D) trabecular bone projection images could be related to three-dimensional (3D) trabecular bone properties such as porosity or connectivity. Two alteration processes were applied to trabecular bone images obtained by magnetic resonance imaging: a trabeculae dilation process and a trabeculae removal process. The trabeculae dilation process was applied from the 3D skeleton graph to the 3D initial structure with constant connectivity. The trabeculae removal process was applied from the initial structure to an altered structure having 99% of porosity, in which both porosity and connectivity were modified during this second process. Gray-level projection images of each of the altered structures were simply obtained by summation of voxels, and fractal dimension (D f ) was calculated. Porosity () and connectivity per unit volume (C v ) were calculated from the 3D structure. Significant relationships were found between D f , , and C v . D f values increased when porosity increased (dilation and removal processes) and when connectivity decreased (only removal process). These variations were in accordance with all previous clinical studies, suggesting that fractal evaluation of trabecular bone projection has real meaning in terms of porosity and connectivity of the 3D architecture. Furthermore, there was a statistically significant linear dependence between D f and C v when remained constant. Porosity is directly related to bone mineral density and fractal dimension can be easily evaluated in clinical routine. These two parameters could be associated to evaluate the connectivity of the structure. (J Bone Miner Res 2000;15:691-699)

23Na relaxation studies of aqueous clay dispersions showed influence of the order/disorder transition of clay gels and the quadrupolar relaxation of neutralizing sodium counterions. Detection of the fast and slow components of the 23Na transverse magnetization gives access to the microstructural and dynamical properties of colloidal dispersions. Numerical simulations of sodium diffusion, using a simplified model of clay dispersion, explain the pathology of the 23Na relaxation rates by the high sensitivity of the quadrupolar coupling to the orientational correlations of charged interfaces. Frequency variation of the NQR relaxation rates of confined counterions therefore appears as a new tool for the investigation of the spatial correlations of charged interfaces within disordered porous media.

2 H NMR spectroscopy, relaxometry, and two-time correlation measurements are used to investigate the structural and dynamical properties of water molecules confined within the multiscale porous network of dense clay sediment. The residual quadrupolar splitting detected by 2 H NMR spectroscopy is the fingerprint of the specific orientation of the water molecules pertaining to the first hydration shell of clay lamellae. Multiquantum 2 H NMR relaxation measurements are used to quantify the distribution of the clay platelet orientations within the dense sediment. The average residence time of the water molecules confined within the clay interlamellar space is determined by exploiting 2 H multiquantum NMR relaxation measurements under spin-locking conditions. Finally, long-time scale diffusion of the water molecules within the multiscale porous network of the clay sediment is quantified by measuring the attenuation of the 2 H NMR two-time stimulated echo.