Almost Ideal 1D Water Diffusion in Imogolite Nanotubes Evidenced by NMR Relaxometry

Abstract

The longitudinal proton relaxation rates R(1) of water diffusing inside synthetic aluminium silicate imogolite nanotubes are measured by fast field-cycling NMR for frequencies between 0.02 and 35 MHz at 25, 37 and 50 degrees C. We give analytical expressions of the dominant intermolecular dipolar spin-spin contribution to R(1) and to the transverse relaxation rate R(2). A remarkable variation of R(1) by more than two orders of magnitude is observed and shown to be close to the theoretical law, inversely proportional to the square root of the resonance frequency, which is characteristic of perfect molecular 1D diffusion. The physics of diffusion is discussed.

The Gadonanotubes as High-Performance MRI Contrast Agents: The Unappreciated Role of the Carbon Nanotube Component at Low Magnetic Fields

“…However, the signature of diffusion inside a nanotube, i.e., 1-dimensional diffusion, is a power law in the Larmor frequency and not the observed dependence on the logarithm of the Larmor frequency. 35 Thus, we must conclude that the effect of 1-dimensional water diffusion inside the nanotubes does not make a dominant contribution to the observed water proton SLR profile. For the GNTs, if the Gd 3+ ions were well inside the nanotubes, one would expect to see the effects of 1-dimensional diffusion reflected strongly in the relaxation dispersion profile.…”

Dynamics of Ionic Liquids in Confinement by Means of NMR Relaxometry—EMIM-FSI in a Silica Matrix as an Example

“…This implies that one is able to probe, in a single experiment, dynamical processes on the time scales from ms tons [ 10 , 12 , 13 ]. Moreover, the shape of the relaxation dispersion profile (spin–lattice relaxation rate versus the resonance frequency) unambiguously reveals the mechanism of motion [ 14 , 15 , 16 , 17 ], also allowing to differentiate between the translation diffusion pathways of different dimensionality: 3D, 2D, 1D [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 ]. Relaxation rates are given as linear combinations of spectral density functions being Fourier transforms of the corresponding time correlation functions, characterising the motion associated with the relaxation process [ 3 , 4 , 5 , 6 , 7 ].…”

NMR Relaxation of Water in Nanostructures: Analysis of Ferromagnetic Cobalt-Ferrite Polyelectrolyte Nanocomposites

“…[28] For instance, almost ideal 1D diffusion has been inferred from the profile of hydrated imogolite nanotubes. [29] In recent work [20] we have rationalised the r 1 profiles of the lipid 1 H fraction in diamagnetic liposomes. Collective membrane motions, which were treated as quasi-spherical fluctuations, were found to dominate the relaxation at low frequency.…”