Water self-diffusion

Parameter setup 3.4. (Example 3.4) Water self-diffusion at 20°C... 

FIG. 24 Water self-diffusion in polyacrylamide gels with various Bis content with comparison to various models from the literature. (Reprinted from Ref. 290, Copyright 1998, Academic Press.)... 

Hadden, DA, Master of Science Thesis, Florida State University, Tallahassee, FL, 1999. Hadden, D Rill, RL McFadden, L Locke, BR, Oligonucleotide and Water Self-Diffusion in Pluronic Triblock Copolymer Gels and Solutions by Pulsed Field Gradient Nuclear Magnetic Resonance, Macromolecules 33, 4235, 2000. 

Malmsten, M Lindman, B, Water Self-Diffusion in Aqueous Block Copolymer Solutions, Macromolecules 25, 5446, 1992. 

FIG. 4 Apparent mole fraction (x) water in continuous phase of brine, decane, and AOT microemulsion system derived from the water self-diffusion data of Fig. 3 using the two-state model of Eq. (1). 

FIG. 5 Order parameter for disperse pseudophase water (percolating clusters versus isolated swollen micelles and nonpercolating clusters) derived from self-diffusion data for brine, decane, and AOT microemulsion system of single-phase region illustrated in Fig. 1. The a and arrow denote the onset of percolation in low-frequency conductivity and a breakpoint in water self-diffusion increase. The other arrow (b) indicates where AOT self-diffusion begins to increase. 

While the order parameters derived from the self-diffusion data provide quantitative estimates of the distribution of water among the competing chemical equilibria for the various pseudophase microstructures, the onset of electrical percolation, the onset of water self-diffusion increase, and the onset of surfactant self-diffusion increase provide experimental markers of the continuous transitions discussed here. The formation of irregular bicontinuous microstructures of low mean curvature occurs after the onset of conductivity increase and coincides with the onset of increase in surfactant self-diffusion. This onset of surfactant diffusion increase is not observed in the acrylamide-driven percolation. This combination of conductivity and self-diffusion yields the possibility of mapping pseudophase transitions within isotropic microemulsions domains. 

FIG. 26 Observed water self-diffusion coefficients as a function of the protein concentration (g protein/g water) for micellar casein dispersions ( ), for acid gels (O), and for rennet gels ( ) [reproduced with permission from Mariette et al (2002)]. 

FIG. 28 Water self-diffusion coefficient plotted as a function of weight fraction of solids for samples of sucrose, instant 1 dent starch, and a 1 1 sucrose/starch mixture at 20 °C. The corresponding weight fractions at the DSC Tg equal to 20 °C are given for reference [reproduced with permission from Kou et al. (1999)]. 

Metais, A. and Mariette, F. 2003. Determination of water self-diffusion coefficient in complex food products by low field h-1 PFG-NMR Comparison between the standard spin-echo sequence and the T-l-weighted spin-echo sequence. J. Magn. Reson. 165, 265-275. 

Proton mobility (D J and water self-diffusion coefficient (D q) as a function of the water volume fraction (X ) in Nafion and SPEEKK, where X, = volume of water in membrane divided by volume of wet membrane. (From Kreuer, K. D. 2001. Journal of Membrane Science 185 29-39.)... 

Water self-diffusion coefficients (Dh o) have been determined by pulse field gradient NMR for Nation (Nil/) , BPSH, and SPEEKK and have been shown to increase with increasing acid and water content. At high water contents, the values for PEMs approach the corresponding value for pure water. This is due to the increase in volume fraction of free water. At low water content, however. Nation exhibits greater Dnp values than either BPSH or SPEEKK. In corranon with the observations for EOD, this has been attributed to the smaller channels in aromatic-based polymers, leading to a considerably lower dielectric constant for the water in the channels. 

The reduction of the long-range diffusivity, Di by a factor of four with respect to bulk water can be attributed to the random morphology of the nanoporous network (i.e., effects of connectivity and tortuosity of nanopores). For comparison, the water self-diffusion coefficient in Nafion measured by PFG-NMR is = 0.58 x 10 cm s at T = 15. Notice that PFG-NMR probes mobilities over length scales > 0.1 /rm. Comparison of QENS and PFG-NMR studies thus reveals that the local mobility of water in Nafion is almost bulk-like within the confined domains at the nanometer scale and that the effective water diffusivity decreases due to the channeling of water molecules through the network of randomly interconnected and tortuous water-filled domains. ... 

Figure 2. Conductivity diffusion coefficient (mobility) of protons and water self-diffusion coefficient of aqueous solutions of hydrochloric acid (HCl), as a function of acid concentration (molarity, M) (data are taken from ref 141).

Figure 9. Proton conductivity diffusion coefficient (mobility) and water self-diffusion coefficient of Nation 117 (EW = 1100 g/equiv), as a function of temperature and the degree of hydration n = [H20]/[—SOsH]). ...

Topgaard, D. (2003). Nuclear Magnetic Resonance Studies of Water Self-diffusion in Porous System. Ph.D. thesis, Lund University, Sweden. 

Hubbard PL, McGrath KM, Callaghan PT (2005) A study of anisotropic water self-diffusion and defects in the lamellar mesophase. Langmuir 21(10) 4340-4346... 

Abstract We use Nuclear Magnetic Resonance relaxometry (i.e. the frequency variation of the NMR relaxation rates) of quadrupolar nucleus ( Na) and H Pulsed Gradient Spin Echo NMR to determine the mobility of the counterions and the water molecules within aqueous dispersions of clays. The local ordering of isotropic dilute clay dispersions is investigated by NMR relaxometry. In contrast, the NMR spectra of the quadrupolar nucleus and the anisotropy of the water self-diffusion tensor clearly exhibit the occurrence of nematic ordering in dense aqueous dispersions. Multi-scale numerical models exploiting molecular orbital quantum calculations, Grand Canonical Monte Carlo simulations, Molecular and Brownian Dynamics are used to interpret the measured water mobility and the ionic quadrupolar relaxation measurements. 

Another descriptor of the mobility of water molecules in contact with the clay layers is the water self-diffusion coefficient. A fine recent review summarizes the theoretical and practical aspects of measurement by spin-echo nmr methods of this parameter (36) The plot of the decrease in the water self-diffusion coefficient as a function of C, the amount of suspended clay, for the same samples, is again a straight line going through the origin. By resorting once more to a similar analysis in terms of a two-state model (bound and "free water), one comes up (25) with a self-diffusion coefficient, for those water molecules pinched in-between counterions and the clay surface, of 1.6 10 15 m2.s 1,... 

Water in skeletal carbonates bound Hp and OH , 106-107,109 liquid Hp in fluid inclusions, 106 Water molecules at day interface, modes of reorientation, 403-404 Water self-diffusion coefficient, measurement, 404-405 Weathering, definition, 4 Wintergreen, triboluminescent spectra, 255259... 

Sposito and co-workers employed a rigid framework for the clay lattice that has been used successfully to predict rf(001) layer spacing, interlayer structure, and water self-diffusion coefficients [62-80], Calculated layer spacings and thermodynamic properties, as well as interlayer water configurations and interlayer-species self-diffusion coefficients are in agreement with available experimental data. 

Diffusion-weighted MRI measures water self-diffusion and depends on (1) diffusion distance within the cells, (2) tortuosity of the interstitial spaces (Helmer et al.,... 

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