Accelerating Restricted Diffusion NMR Studies with Time-Resolved and Ultrafast Methods

Abstract

Restricted diffusion of fluids in porous materials can be studied by pulsed field gradient nuclear magnetic resonance (NMR) non-invasively and without tracers. If the experiment is repeated many times with varying diffusion delays, detailed information about pore sizes and tortuosity can be recorded. However, the measurements are very time-consuming because numerous repetitions are needed for gradient ramping and varying diffusion delays. In this paper, we demonstrate two different strategies for acceleration of the restricted diffusion NMR measurements: time-resolved diffusion NMR and ultrafast Laplace NMR. The former is based on time-resolved non-uniform sampling, while the latter relies on spatial encoding of two-dimensional data. Both techniques allow similar 1–2 order of magnitude acceleration of acquisition, but they have different strengths and weaknesses, which we discuss in detail. The feasibility of the methods was proven by investigating restricted diffusion of water inside tracheid cells of thermally modified pine wood.

Decay of a Roman age pine wood studied by micro magnetic resonance imaging, diffusion nuclear magnetic resonance and portable nuclear magnetic resonance

“…Therefore, we likely underestimated the value of tortuosity. Nevertheless, the tortuosity value obtained for modern pine seems to be in agreement with the literature value around 10 calculated for thermally modified Pinus sylvestris , also considering the effect of thermal modification and that we used a different species (Pinus pinea) [61]. Moreover, tortuosity is also in good agreement with the diffusion coefficient and diameters results.…”

“…This indicates a continuous distribution among earlywood and latewood tracheids, likely with water exchange. For modern wood, the two predominant peaks as well as their probability in Figure 5b) are in good agreement with the diameters calculated from diffusion analyses, with the MR images and with the literature values [61], [66] in which the mean lumen diameter was found around 15 µm -20 µm. The existence of two separate peaks shows distinct spins populations for earlywood and latewood.…”

Recent Progress in Liquid State Electrochemistry Coupled with NMR Spectroscopy

“…However, when the molecules with overlapping signals diffuse at different rates, the signals can be resolved by adding the diffusion dimension to the NMR spectra [108–110] . Contrary to the pure‐shift methods, the NMR diffusometry does not require field uniformity and can be measured in the setup with a stray field [111] or with an inhomogeneous sample [112,113] . The problem, however, arises when a high chemical resolution is required.…”

Deeper Insight into Photopolymerization: The Synergy of Time-Resolved Nonuniform Sampling and Diffusion NMR

“…Both methods arose concomitantly, and they possess somewhat orthogonal strengths and weaknesses. 19 While the UF method allows much faster sampling leading to much better time resolution, the TR methods are more stable in out-of-equilibrium conditions. Therefore, the TR is a more optimal choice for photopolymerization monitoring, where the light source might cause additional disturbances in the system.…”