NMR Self-Diffusion Coefficient

The NMR self-diffusion coefficient measurements also provide a convenient tool for the study of the micellization process. They are based on the large... 

By listing the ratios of the molar conductivities versus the conductivities calculated from the NMR self-diffusion coefficients A m /ANV(R, they were able to propose a useful parameter to characterize various properties of ILs with different anions, such as quantitative information on how much individual ions contribute to ionic conduction. 

NMR self-diffusion coefficients (Lindman, 1983), small-angle neutron scattering (SANS) (Cebula, 1982 Triolo, 1983 Corti, 1984), freezing point and vapor pressure methods (Herrington, 1986) and fluorescent probes (Atik, 1979) have been used to calculate aggregation numbers of several different types of surfactants (Zana, 1980 Lianos, 1980, 1981, 1982, 1983). Some aggregation numbers of surfactants are listed in Table 3-1. 

Covering temperatures from -140 up to 200 C and chain lengths from one to six carbon atoms, the intracrystalline mean life times are found to coincide with the values oi rV 1 r calculated from the nmr self-diffusion coefficients. This clearly indicates that molecular exchange is controlled by intracrystalline self-diffusion, and that for the considered adsorbate-adsorbent systems there are no perceptible surface barriers. 

FIGURE 8.11 (a) Circles represent diffusivities from the synthetic boundary method, squares from DLS, and triangles are NMR self-diffusion coefficients. The system is ovalbumin with very little electrolyte and close to the isoelectric point, (b) Mutual diffusivities corrected for the solution nonideality compared to NMR results (line). Reprinted from Gibbs et al. (1991) with permission. Copyright 1978 American Chemical Society. 

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. 

The effect of salt concentration on intermicellar interactions and aggregate structures of anionic and cationic-rich mixtures of CTAB (cetyltrimethylammonium bromide) and SDS (sodium dodecyl sulfate) were investigated with conductometry, surface tension, zeta potential, cyclic voltammetry measurements and by determining the surfactant NMR self-diffusion coefficients. ... 

We have shown PFG-NMR-derived diffusion coefficients can be used to calculate molar conductivity and compared with impedance measurements to understand ionicity. In a somewhat reversed experiment, diffusion coefficients measured electrochemicaUy have been compared to PFG-NMR self-diffusion coefficients to investigate proton transfer in protic ILs [19]. Aside from probing ionization dynamics in ILs, PFG-NMR has also been used for probing aggregation as shown in Fig. 5, especially for... 

Figure 3. (sO The inverse of the NMR self diffusion coefficient 1/D versus 1/T (squares the bulk water and circles the protein hydration one). The, 1 /Z> behavior identifies two crossovers one at the FSC temperature Tl (223K) and one at a higher temperature To) in the region of the protein denaturation. (b) The thermal evolution of the longitudinal NMR relaxation time Ti 19. ... 

Judeinstein P, lojoiu C, Sanchez JY et al (2008) Proton conducting ionic liquid organization as probed by NMR self-diffusion coefficients and heteronuclear correlations. J Phys Chem B 112 3680-3683... 

The use of NMR self-diffusion coefficients clearly demonstrated that a water-in-oil type microemulsion exists. The transition from water-in-oil to bicontinuous microemulsion and finally to an oil-in-water system by increasing the water-IL content can be detected by considering the change in the diffusion coefficients. 

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