“Relaxometry” experiments and analysis of dispersion curves: An illustrative example of toluene in liquid and in organogel phases

Abstract

At very low or low frequency, the so-called dispersion curves (longitudinal relaxation rate as a function of the measurement frequency) are obtained with a ''relaxometer,'' which is generally run according to the ''field-cycling'' technique. Because of the very poor field homogeneity, relaxation times of a single (broad) signal are measured. When going to higher fields, with standard nuclear magnetic resonance spectrometers (possibly with variable field capacities), different lines are resolved. We show how the relaxation rates pertaining to these lines can be connected to the results obtained via the relaxometer. Among other things, we demonstrate why the magnitude mode (generally used for processing the relaxometer data) must be used with caution when several lines are resolved. Actually, we could obtain accurate 1 H dispersion curves in a very broad frequency range (5 kHz-400 MHz), and we show that a decomposition into several Lorentzian curves proves to be adequate, as far as paramagnetic relaxation due to dissolved oxygen is concerned. The method will be applied i) to nondegassed liquid toluene, ii) to the same solvent involved in the formation of an organogel. In that latter case, a low frequency contribution to the dispersion curve (possibly non-Lorentzian) reveals the part of the solvent within the organogel structure. The algorithm used for analyzing these dispersion curves is described.

Thermal Properties, Conductivity, and Spin-lattice Relaxation of Gel Electrolyte Based on Low Molecular Weight Gelator and Solution of High Temperature Ionic Liquid

“…Therefore, it is experimentally difficult to detect the adsorbate molecules but possible thanks to the field cycling NMR relaxometry method [42][43][44]. It is the most suitable NMR method for the identification and characterization of molecular dynamics in porous media and has been successfully applied to study the solvent dynamics in molecular gels [33,34,36,[55][56][57][58]. Through the solvent dynamics studies we were able to detect the solvent-gelator interactions in some of the molecular gels [33,36,37,55,58].…”

Novel supramolecular organogels based on a hydrazide derivative: non-polar solvent-assisted self-assembly, selective gelation properties, nanostructure, solvent dynamics

“…Recently, this method was applied to organogels in which an increase in the correlation time of a solvent conned in the gel matrix was also detected. 24,[57][58][59] It was due to the solvent-gelator interactions manifested by the dispersion of the spin-lattice relaxation time of the solvent in the low frequency range, below 10 6 Hz. Herein, we performed the spin-lattice relaxometry measurements to obtain the information about the dynamics of benzene, toluene, and p-xylene in the gels studied and about the interaction of these solvents with gelator 1 aggregates.…”

Nuclear spin relaxation in liquids and gases

“…Tritt-Goc and co-workers 306 studied the interaction between chlorobenzene and a low-molecular mass gelator, using the FFC relaxometry. Steiner et al 307 described the measurements of fielddependent proton relaxation rates and the analysis of the NMRD curves, using neat toluene and toluene in an organogel as examples. Centomo et al 308 studied water-swelling of copolymer matrices using, among other techniques, proton T 1 and T 2 measurements at a (single) low magnetic field.…”