NMR-detected tracer technique to measure diffusion in condensed matter

Abstract

A simple method to study di †usion with the help of NMR has been suggested, based on the measurement of the rate of establishment of equilibrium in a sample with initial non-equilibrium distribution of labelled species. The distribution of components in the sample during the process of di †usion was determined with the use of a standard NMR spectrometer or relaxometer. Di †usion coefficients, D, measured in water and the plastic phase of sulfolane agreed well with the data obtained by other methods. D values for dioxane in cross-linked polyurethane and for water in the lamellar phase of waterÈammonium per-Ñuorononanoate (APFN) mixtures were also measured, to demonstrate the application of the method. The technique, being a tracer method, can be applied in a number of cases where the application of spin-echo is difficult (e.g. low concentration of solvent in polymers, in conditions of incomplete averaging of internal Ðelds, large chemical shifts etc.) ; for the study of mutual di †usion and dissolution kinetics of complex phase mixtures ; and for the measurement of D in systems with physical hindrances to di †usion where the method allows one to determine D corresponding to " inÐnite Ï time of observation.The proposed method has its origin in the property of NMR phenomena, that the integral intensity of the detected signal is proportional to the number of resonating nuclei in the volume of the rf coil of the spectrometer. Thus it is possible to determine the absolute or the relative concentration of a substance in any part of the cylindrical tube used in the NMR investigation. In the presented method, two chemically identical substances (or mixtures in the case of multicomponent systems) but with di †erent isotopic content are put into contact directly in the NMR tube and the change in concentration of one (or both) components with time is observed along the NMR tube. The integral intensity of the NMR spectrum or the maximum amplitude of the free precession signal is measured. D is calculated from the time dependence of the NMR signal. Previously, NMR has been applied to monitor the change in concentration of a labelled species.1h4 However, in this study, for the Ðrst time, the initial, non-equilibrium distribution of isotopic species was used, allowing one, in principle, to Ðnd the self-di †usion coefficient. Since the chemical potentials of both samples are very close, the measured value in many cases reÑects the " true Ï translational mobility (selfdi †usion, intradi †usion), which is di †erent from mutual di †usion. The driving force of the latter is the di †erence in chemical potentials of the two samples.5h9The method was applied to the determination of D in water and polycrystalline sulfolane in the plastic state and gave results which were in a good agreement with those determined by other methods.10,11 It was supposed that this method could be applied to other systems including liquids, liquid crystals, polymer solutions etc., in which the widely used spinecho technique might have difficulties due to non-...

NMR methods applied to anisotropic diffusion

“…1 -3 One should note that NMR in combination with imaging can also be used for tracing the advancing front of isotopically 197,198 or chemically 199 or by shear concentration 16,199 -205 distinguishable materials. Hence NMR spectrometers can be adapted for tracer-type diffusion studies and thereby access self- 197,198 or transport 16,199 -205 diffusion under some circumstances. Examples of applications to anisotropic diffusion 197,198 are, as yet, rare.…”

“…Hence NMR spectrometers can be adapted for tracer-type diffusion studies and thereby access self- 197,198 or transport 16,199 -205 diffusion under some circumstances. Examples of applications to anisotropic diffusion 197,198 are, as yet, rare.…”

Determination of the Diffusivity of a Hydrophilic Migratory Additive in Ipp Films

“…The weight of plain PP film, the control specimen, did not change during the surface-washing process. By using time (in seconds) as the variable and knowing the half thickness (L ¼ 37.5 mm), each data set in Figure 2 was fitted to Equation (11) or (12) to get D by the method of least squares, according to the concentration level. The average of three measurements is shown in Figure 3(a).…”

“…The characterization of additive diffusivity in plastics is an important area of study in order to understand the performance of a material. There has been much work in diffusivity measurement by mapping concentration profiles along the diffusion path through various techniques, such as FTIR [2][3][4], fluorescence recovery [5][6][7], ultraviolet microscopy [8,9], NMR using labeled tracer additive [10,11], refractive index-related optical spectroscopy [12], and thermogravimetric methods [13]. There are many studies where the additives leach out from a plastic film over time into surrounding liquids of lower additive concentration [6][7][8][9][10][14][15][16]], but only a few studies where the additives diffuse from an additive-containing film or solution into a plain plastic film [4,13].…”