Nuclear magnetic resonance spectroscopy self-diffusion

It is possible to examine experimentally both the diffusion in a liquid crystal of its own molecules (self-diffusion) and the diffusion of impurities. The coefficients of self-diffusion are determined by various methods, e.g., quasi-elastic neutron scattering [100], the diffusion of tracer (radioactive) molecules [101], or the spin-echo methods in nuclear magnetic resonance spectroscopy [102]. The last method is probably the most reliable. Essentially, it is as follows initially the spins of the molecular protons are polarized by a marked pulse of a radio-frequency field then the molecules... 

The different mobilities of monomers versus micelles can be used as a means to determine the value of CMC. The self-diffusion coefficients of the water and surfactant can be measured by pulsed-gradient spin Fourier-transform nuclear magnetic resonance echo (FT-NMR) spectroscopy, following the NMR spectra (13). Hence, a plot of the diffusion coefficient D versus the surfactant concentration shows a change in slope corresponding to the CMC. 

Nuclear magnetic resonance (NMR) spectroscopy is an especially useful molecular probe of water properties." " The self-diffusion coefficient of water Dg has been measured, using a spin-echo technique, over a considerable range of temperatures and densities. This method complements the more direct tracer diffusion method. With one interesting exception, Dg increases with increasing temperature and decreases with increasing pressure. The exception occurs for temperatures in the 275-323 K range and for pressures up to about... 

This section is concerned with measurement techniques of the diffusivity and solubility from which the permeability can easily be calculated. In the following analysis we restrict ourselves to the measurement of constant values of D. Concentration- and position-dependent diffusivities are analyzed in Crank and Park (1968) and Crank (1975). Generally, the techniques are for permeability, steady-state and time lag techniques and for diffusivity, sorption and desorption kinetics and concentration-distance curves. For self-diffusivity in polymer melts the techniques are (Tirrell, 1984) nuclear magnetic resonance, neutron scattering, radioactive tracer, and infrared spectroscopy. 

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