Abstract
Nuclear magnetic relaxation is useful for probing physical and chemical properties of liquids in porous media. Examples are given on high surface area porous materials including calibrated porous silica glasses, granular packings, plaster pastes, cement-based materials and natural porous materials, such as sandstone and carbonate rocks. Here, we outline our recent NMR relaxation work for these very different porous materials. For instance, low field NMR relaxation of water in calibrated granular packings leads to striking different pore-size dependencies of the relaxation times T1 and T2 when changing the amount of surface paramagnetic impurities. This allows separation of the diffusion and surface limited regimes of relaxation in these macroporous media. The magnetic field dependence of the nuclear spin–lattice relaxation rate 1/T1(ω0) is also a rich source of dynamical information for characterizing the molecular dynamics of liquids in porous media. This allows a continuous characterization of the evolving microstructure of various cementitious materials. Our recent applications of two-dimensional (2D) T1–T2 and T2-z-store-T2 correlation experiments have evidenced the water exchange in connected micropores of cement pastes. The direct probing of water adsorption time on a solid surface gives access to an original characterization of the surface nano-wettability of porous plaster pastes. We show that such a parameter depends directly on the physical chemistry of the pore surfaces. Lastly, we outline our recent measurements of wettability in oil/brine/reservoir carbonate rocks.
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GENERAL SCIENTIFIC SUMMARY Introduction and background. Nuclear magnetic relaxation in a large range of magnetic fields is useful for probing the physical and chemical properties of liquids in disordered porous media. Examples are given on high surface area porous materials, including calibrated porous silica glasses, granular packings, plaster pastes, cement-based materials and natural porous materials such as sandstone and carbonate rocks.
Main results. We outline our recent NMR relaxation work for these very different porous materials. For instance, low-field NMR relaxation of water in calibrated granular packings leads to strikingly different pore-size dependences of the relaxation times T1 and T2 when changing the quantity of surface paramagnetic impurities. This allows separation of the diffusion and surface-limited regimes of relaxation in these macroporous media. The magnetic field dependence of the nuclear spin-lattice relaxation rate 1/T1(ω0) is also a rich source of dynamical information for characterizing the molecular dynamics of liquids in porous media. This allows a continuous characterization of the evolving microstructure of various cementitious materials, namely the specific surface area. Our recent applications of two-dimensional T1–T2 and T2-z-store-T2 correlation experiments have evidenced, for the first time, water exchange in connected micropores of cement pastes. We directly probe the water adsorption time and the nano-wettability of porous plaster pastes. Lastly, we outline our recent in situ measurements of wettability in oil/brine/reservoir carbonate rocks.
Wider implications. Both the NMR methods and the theories presented can be applied more widely to any porous media with reactive surfaces involving liquid confinement, such as those encountered in oil recovery, heterogenous catalysts, biological tissues and foodstuffs.
Figure. 1H spin-lattice relaxation rate of a white cement paste hydrated with w/c = 0.4 as a function of the hydration time measured at a Larmor frequency of 10 kHz in white cement. The weighting factors for each of the relaxation components are indicated. The inset represents the NMR-specific surface area deduced from the data in the main figure.