Nuclear magnetic resonance relaxometry as a method of measuring translational diffusion coefficients in liquids

Abstract

By application of the field-cycling technique, we measure the dispersion of the (1)H nuclear magnetic resonance (NMR) spin-lattice relaxation time T(1)(ω) for a series of molecular liquids. We demonstrate that such NMR relaxometry studies can be used for determining diffusion coefficients. A broad frequency range of 10 kHz-20 MHz is covered. By scanning T(1)(ω) one directly probes the spectral density of the diffusion processes. The value of the diffusion coefficient D can be determined from a linear dependence of the (1)H spin-lattice relaxation rate on the square root of the frequency at which it is measured. The power of this method lies in its simplicity, which allows one to determine D(T) independently of the diffusive model. The results obtained are in very good agreement with those of field gradient NMR methods.

Interpretation of 1H and 2H spin–lattice relaxation dispersions: Insights from molecular dynamics simulations of polymer melts

“…While rotational motion dominates the intramolecular part, translational motion manifests itself in the inter-molecular part, in particular, at long times and low frequencies [21,27]. In the following, we take a closer look at the intra-and inter-molecular parts.…”

“…While some studies argued that, due to the strong distance dependence of the dipolar couplings, 1 H SLR is dominated by the inter-molecular part [17,28,30,31], others emphasized that the inter-molecular part must not be neglected, in particular, at long times [13,14,20,21]. To shed light on the relevance of intra-and inter-molecular contributions to 1 H SLR, G intra (t) and G inter (t) are compared for PEO 12 at 265 K in Fig.…”

“…Moreover, the translational correlation time τ T is related to the relative diffusion coefficient, which, in turn, is twice the selfdiffusion coefficient for a system of identical particles, in detail, 2D ¼ d 2 =τ T . Hence, analysis of the inter-molecular correlation function provides access to the self-diffusion coefficient D [20,21]. However, this approach rests on the assumption of free diffusion, which is not necessarily found in the time window of the experiment for complex fluids.…”

“…Then, it is possible to interpret the experimental results in terms of autocorrelation functions of rotational motion. However, previous works [13,14,20,21] showed that, for sufficiently low resonance frequencies, inter-molecular contributions can govern the relaxation behavior. In such situation, the low-frequency data provide access to translational motion, e.g., to self-diffusion coefficients D. Thus, 1 H FFC has the potential to yield detailed insights into both rotational and translational dynamics.…”

Multi-Quanta Spin-Locking Nuclear Magnetic Resonance Relaxation Measurements: An Analysis of the Long-Time Dynamical Properties of Ions and Water Molecules Confined within Dense Clay Sediments

“…In addition to NMR relaxation measurements performed at a limited number of available magnetic fields [16,33], spin-locking relaxation measurements [16,33,[40][41][42][43] were initially performed to extend the investigation of the dispersion curves to lower magnetic fields. These two complementary procedures lead however to a large gap within the dispersion curves that was successfully filled recently by field cycling NMR relaxometry [29][30][31][32][44][45][46][47][48]. Unfortunately, in the case of confined quadrupolar nuclei, the enhancement of the transverse relaxation rate of the confined quadrupolar probes prohibits the use of field cycling NMR relaxometry because of the time required to switch the magnetic field.…”