¹H NMR Relaxometry and Diffusometry Study of Magnetic and Nonmagnetic Ionic Liquid-Based Solutions: Cosolvent and Temperature Effects

Abstract

In this work, H NMR relaxometry and diffusometry as well as viscometry experiments were carried out as a means to study the molecular dynamics of magnetic and nonmagnetic ionic liquid-based systems. In order to evaluate the effect of a cosolvent on the superparamagnetic properties observed for Aliquat-iron-based magnetic ionic liquids, mixtures comprising different concentrations, 1% and 10% (v/v), of DMSO-d6 were prepared and studied. The results for both magnetic and nonmagnetic systems were consistently analyzed an suggest that, when at low concentrations, DMSO-d6 promotes more structured ionic arrangements, thus enhancing these superparamagnetic properties. Furthermore, the analysis of temperature and water concentration effects allowed to conclude that neither one of these variables significantly affected the superparamagnetic properties of the studied magnetic ionic liquids.

Dynamics of Dimethylbutanols in Plastic Crystalline Phases by Field Cycling 1H NMR Relaxometry

“…In fact, for highly symmetric lattices, as those of plastic crystals usually are, isotropic diffusion for which the single jump distance has always the same value can be considered a good approximation of lattice diffusion , where r is the distance of closest approach of two protons and the other parameters have the same meaning as in eq . is an analytical and dimensionless function that depends on r , on the mean square of the jump length ⟨ r j 2 ⟩, and on the mean time between jumps τ SD (the expression of is lengthy, so we refrain from showing it here).…”

“…This renders the analysis of nuclear magnetic relaxation dispersion (NMRD) curves (i.e., R 1 = 1/ T 1 vs Larmor frequency curves) quite complex and, in some cases, dependent on the choice of the models devised for the description of contributions to R 1 arising from internal and overall molecular reorientations, and self-diffusion motion. In spite of this, FFC 1 H NMR relaxometry has been increasingly employed to investigate dynamics in condensed matter. − Self-diffusion coefficients ( D ) and rotational correlation times were determined from the analysis of NMRD curves for molecular and ionic liquids ,− and for liquid crystals, − but only for few plastic crystals. , The linear dependence of R 1 on the square root of the Larmor frequency (ν) at low frequencies, theoretically predicted for translational motion in three dimensions, − allowed an independent determination of D for some of them. ,,− , …”

Tuning the 1H NMR Paramagnetic Relaxation Enhancement and Local Order of [Aliquat]+-Based Systems Mixed with DMSO

“…As the OPF and the translational diffusional mechanisms are most effective within the same frequency range, it is possible to have either one as the most important for relaxation. However, by applying the methods and models described above to [Aliquat][Cl] NMRD profiles at different temperatures [8], and taking into account the fact that f min ∝ 1/(ηξ 2 ) should increase with temperature, it is possible to conclude that the OPF mechanism must dominate over self-diffusion (see Appendix A.1). These fits can be accessed in the Supplementary Materials-Figure S1.…”

“…Average molar mass, density, spin density and molar concentration of magnetic particles of the studied systems. (*)-samples reported in Beira et al[8].…”

“…Beira et al [8] have presented a 1 H NMR relaxometry and diffusometry study of mixtures comprising [Aliquat] [Cl] [Aliquat] [FeCl 4 ] and deuterated dimethyl sulfoxide, DMSO-d6, demonstrating that concentrations of DMSO below 10% (v/v) enable a significant reduction of the viscosity of these systems without compromising the PRE induced by the presence of iron in the mixtures. This work motivated the present study, which offers a more consistent analysis of the [Aliquat] + and DMSO-based binary and ternary compounds, taking into consideration much larger DMSO concentrations, an important contribution of the inner-sphere paramagnetic relaxation mechanism and local aggregate changes related with different DMSO concentrations.…”