Nuclear magnetic resonance measured diffusion coefficient

There are other physical measurements which reflect molecular mobility and can be related to relaxation times and friction coefficients similar to those which characterize the rates of viscoelastic relaxations. Although such phenomena are outside the scope of this book, they are mentioned here because in some cases their dependence on temperature and other variables can be described by reduced variables and, by means of equation 49 or modifications of it, free volume parameters can be deduced which are closely related to those obtained from viscoelastic data. These include measurements of dispersion of the dielectric constant, nuclear magnetic resonance relaxation, diffusion of small molecules through polymers, and diffusion-controlled aspects of crystallization and polymerization. 

Balcom, B Fischer, A Carpenter, T Hall, L, Diffusion in Aqueous Gels. Mutual Diffusion Coefficients Measured by One-Dimensional Nuclear Magnetic Resonance Imaging, Journal of the American Chemical Society 115, 3300, 1993. 

Some of the methods for measuring molecular diffusion coefficients, together with a few recent references, are (a) diaphragm cell [60,61] (b) boundary layer interferometry [59] (c) shearing plate interferometry [58] (d) chromatographic peak broadening [60] (e) nuclear magnetic resonance and electron spin resonance [62, 63] (f) electrolyte conductance [64] (g) isotopic tracers [65] and (h) laminar jets [66]. 

Rotational diffusion is characterized by the mean square angular deviation during the time interval At (0 ) = GDrAi. Highly anisotropic motion, which is typical for lipid molecules in the membrane, is usually described by two rotational diffusion coefficients Dr and Dri, which correspond to diffusion about the long diffusion axis and perpendicular to it, respectively. The diffusion coefficients are related to corresponding rotational correlation times measured by nuclear magnetic resonance (NMR), electron spin resonance (ESR), fluorescent depolarization, and so on, as ... 

The diffusion coefficient can also be determined from measurements of other phenomena that are controlled by the activated motion of atoms. These indirect methods include internal friction measurements, nuclear magnetic resonance spectra, and some magnetic relaxation phenomena (in ferromagnetic substances). These techniques are advantageous in allowing the measurement of D at lower temperatures than are practicable by the conventional methods. 

Eccles, C.D., Callaghan, P.T., and Jenner, C.F., Measurement of the self-diffusion coefficient of water as a function of position in wheat grain using nuclear magnetic resonance imaging, Biophys. J., 53 75, 1988. 

Some of the most successful methods of nuclear magnetic resonance used in the study of disordered porous media have been reviewed and their applications to the measurement of pore size distribution, diffusion coefficients and permeability have been presented. This is the case of nuclear relaxation and pulsed field gradient method of a specific imbibed solvent in various fully or partially saturated organic or inorganic porous media. The cases of narrow and large distributions of pores have been... 

Various experiments indicate that properties of the microemulsion phase change continuously with increasing salinity as inversion from a water-continuous to an oil-continuous microstrucmre occurs. For instance, electrical conductivity decreases continuously with increasing salinity (Bennett et al., 1982). In addition, the self-diffusion coefficient of oil as measured by nuclear magnetic resonance (NMR) techniques increases from small values at low salinities where oil is the dispersed phase to a value comparable to that of the bulk oil phase near and above the optimal sahnity. The self-diffusion coefficient of water, in contrast, decreases from a value comparable to that in pnre NaCl brine below and near the optimal sahnity to mnch smaller values at high salinities where water is the dispersed phase (Olsson et al., 1986). Thus the surfactant phase is bicontinuous near the optimal sahnity, as originahy proposed by Scriven (1976) and subsequently confirmed by electron microscopy (Jahn and Strey, 1988). 

Nuclear magnetic resonance methods have become very useful in measuring diffusion coefficients, but, as in DLS, it becomes more difficult to determine what is being measured as the system gets more complex. The measured diffusivity is most often called the NMR self-diffusion coefficient, but in many instances it is the traditional diffusivity, discussed in Section 4. 

Measurement of Self-Diffusion Coefficient What is measured in DLS is D. DLS cannot measure because it does not distinguish one solute from another. It is necessary to use other more specialized techniques such as forced Rayleigh scattering (FRS), fluorescence recovery after photo-bleaching (FRAP), and pulsed-field gradient nuclear magnetic resonance (PFG-NMR). 

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