Water Mobility within Compacted Clay Samples: Multi-Scale Analysis Exploiting¹H NMR Pulsed Gradient Spin Echo and Magnetic Resonance Imaging of Water Density Profiles

Abstract

1 H NMR pulsed gradient spin echo attenuation and water density profile analysis by magnetic resonance imaging are both used to determine the mobility of water molecules confined within a porous network of compacted kaolinite clay sample (total porosity of ∼50%). These two complementary experimental procedures efficiently probe molecular diffusion within time scales varying between milliseconds and few hours, filling the gap between the time scale of diffusion dynamics measured by traditional quasi elastic neutron scattering and through-diffusion methods. Furthermore, magnetic resonance imaging is a nondestructive investigation tool that is able to assess the effect of the local structure on the macroscopic mobility of the diffusing probe.

A Multi-Scale Study of Water Dynamics under Confinement, Exploiting Numerical Simulations in Relation to NMR Relaxometry, PGSE and NMR Micro-Imaging Experiments: An Application to the Clay/Water Interface

“…It was two orders of magnitude smaller than the maximum resolution of these PGSE measurements. We did not detect significant variation of the self-diffusion coefficient as a function of diffusion time ∆ [29]. As displayed in Figure 14, the attenuation perfectly fit a Gaussien relationship, whatever the direction probed by the applied field gradient.…”

“…Three different classes of clay materials were used in that study: aqueous diluted dispersions [49], dense sediments [23] with a well-controlled hydration state and compacted aggregates [29]. While swelling clays (montmorillonie [50], beidellite [23]) are implied in the two first studies, the samples of the third study are prepared with kaolinite, i.e., unswelling clay [29]. The swelling clays result from the sandwiching of one octahedral layer of aluminum or magnesium oxides between two layers of tetrahedral silicon oxides.…”

“…Details on the time delays, pulse durations and strengths of the magnetic field gradients G are given in the text. Reprinted with permission from [29]. Copyright (2018) American Chemical Society.…”

“…In that context, a large number of experimental studies, including inelastic neutron scattering (INS) [13][14][15], quasi-elastic neutron scattering (QENS) [16,17], neutron spin echo [18], multi-quanta nuclear magnetic resonance (NMR) relaxometry (i.e., the frequency variation of the NMR relaxation rates) [19][20][21][22][23][24], NMR pulsed-gradient spin-echo (PGSE) attenuation [25][26][27][28][29][30] and NMR micro-imaging [29,30], were performed to quantify the mobility of confined water molecules over a broad range of diffusing time. The short times of mobility for the confined water molecules (from pico-seconds up to 100 nanoseconds) were easily probed by classical neutron scattering experiments (INS, QENS and neutron spin echo).…”

“…More details on the selected diffusion directors e i are given (see text above), leading to the components of the self-diffusion tensor D 1 = 1.041 × 10 −9 m 2 /s, D 2 = 1.062 × 10 −9 m 2 /s, D 3 = 0.918 × 10 −9 m 2 /s, D 4 = 1.067 × 10 −9 m 2 /s, D 5 = 0.991 × 10 −9 m 2 /s, and D 6 = 0.992 × 10 −9 m 2 /s. Reprinted with permission from[29]. Copyright (2018) American Chemical Society.…”