Water molecules diffusion coefficient

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. ... 

Water molecules diffusing past each other cause further intermolecular magnetic dipole-dipole interactions. These are a function of the concentration of spins, N, the average diffusion coefficient, D, and the distance of closest approach between the spins, b. 

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... 

Diffusion is a physical process that involves the random motion of molecules as they collide with other molecules (Brownian motion) and, on a macroscopic scale, move from one part of a system to another. The average distance that molecules move per unit time is described by a physical constant called the diffusion coefficient, D (in units of mm2/s). In pure water, molecules diffuse at a rate of approximately 3xl0"3 mm2 s 1 at 37°C. The factors influencing diffusion in a solution (or self-diffusion in a pure liquid) are molecular weight, intermolecular... 

Tapping mode atomic force microscopy Water molecules per acid site, H2O/SO3H Fickian diffusion coefficient of water Self-diffusion coefficient of water Proton mobility Electroosmotic drag coefficient Bulk membrane proton resistance Uncompensated resistance Glass transition temperatme Water volume fraction... 

Example 7.7 For rhodamine 6G molecules in water the diffusion coefficient is D = 2.8 X 10 m /s. In a cylindrical observation volume V = 3 X 10 m with w = 10 pm and a length z = 1 mm the radial diffusion time becomes td = uP-jAD = 89 ms. Since the axial diffusion time is much longer, it does not play a significant role fort he fluctuations. 

The diffusion coefficients of water are in the range of 3.5 — 9.8 x 10 cm /s, which are of the same order of magnitude as the experimental value of about 2 X 10 cm /s measured by pulsed field gradient diffusion NMR [194]. Comparing this with the diffusion coefficient of 2.6 x 10 cm /s in a pure SPC/E water system, one can conclude that in the PSS/PDADMA PECs under study the water molecules diffuse about two orders of magnitude slower than in the pure water system. Therefore, the obtained results of the water diffusion lead to the same conclusion as our dielectric measurements water molecules inside PE mixtures exhibit a slow dynamics when compared to water molecules in a bulk environment. 

RbCl interfacial water is due to a higher RbCl saturation solution concentration. The variation of interfacial water residence time is in excellent agreement with water self-diffusion coefficients. In bulk solutions, water molecules move faster when compared with water molecules at crystal lattice positions and interfacial water molecules as indicated by the short residence times and large diffusion coefficients. For water molecules in bulk KCl solution, the residence time (5.9 ps) and self-diffusion coefficient ( 2.5 X 10 m /sec) are very close to the values for pure water ( 5 ps and 2.5 x 10 mVsec, respectively) (Du and Miller 2007c Koneshan et al. 1998 Koneshan and Rasaiah 2000). 

Diamagnetic electrolyte solutions Intermolecular nuclear magnetic relaxation rate of proton in water molecules correlation times for molecular rotation in free water and hydrated water self diffusion coefficients of water molecules 84, 85... 

The oil droplets in a certain benzene-water emulsion are nearly uniform in size and show a diffusion coefficient of 3.75 x 10 cm /sec at 25°C. Estimate the number of benzene molecules in each droplet. 

Here / is the number of ink molecules diffusing down the concentration gradient per second per unit area it is called the flux of molecules (Fig. 18.3). The quantity c is the concentration of ink molecules in the water, defined as the number of ink molecules per unit volume of the ink-water solution and D is the diffusion coefficient for ink in water - it has units of m s . ... 

Among the dynamical properties the ones most frequently studied are the lateral diffusion coefficient for water motion parallel to the interface, re-orientational motion near the interface, and the residence time of water molecules near the interface. Occasionally the single particle dynamics is further analyzed on the basis of the spectral densities of motion. Benjamin studied the dynamics of ion transfer across liquid/liquid interfaces and calculated the parameters of a kinetic model for these processes [10]. Reaction rate constants for electron transfer reactions were also derived for electron transfer reactions [11-19]. More recently, systematic studies were performed concerning water and ion transport through cylindrical pores [20-24] and water mobility in disordered polymers [25,26]. 

Lateral density fluctuations are mostly confined to the adsorbed water layer. The lateral density distributions are conveniently characterized by scatter plots of oxygen coordinates in the surface plane. Fig. 6 shows such scatter plots of water molecules in the first (left) and second layer (right) near the Hg(l 11) surface. Here, a dot is plotted at the oxygen atom position at intervals of 0.1 ps. In the first layer, the oxygen distribution clearly shows the structure of the substrate lattice. In the second layer, the distribution is almost isotropic. In the first layer, the oxygen motion is predominantly oscillatory rather than diffusive. The self-diffusion coefficient in the adsorbate layer is strongly reduced compared to the second or third layer [127]. The data in Fig. 6 are qualitatively similar to those obtained in the group of Berkowitz and coworkers [62,128-130]. These authors compared the structure near Pt(lOO) and Pt(lll) in detail and also noted that the motion of water in the first layer is oscillatory about equilibrium positions and thus characteristic of a solid phase, while the motion in the second layer has more... 

The values for the lipid molecules compare well (althoughJgiey are still somewhat larger) with the experimental value of 1.5x10 cm /s as measured with the use of a nitroxide spin label. We note that the discrepancy of one order of magnitude, as found in the previous simulation with simplified head groups, is no longer observed. Hence we may safely conclude that the diffusion coefficient of the lipid molecules is determined by hydrodynamic interactions of the head groups with the aqueous layer rather than by the interactions within the lipid layer. The diffusion coefficient of water is about three times smaller than the value of the pure model water thus the water in the bilayer diffuses about three times slower than in the bulk. 

For the analysis of the dynamical properties of the water and ions, the simulation cell is divided into eight subshells of thickness 3.0A and of height equal to the height of one turn of DNA. The dynamical properties, such as diffusion coefficients and velocity autocorrelation functions, of the water molecules and the ions are computed in various shells. From the study of the dipole orientational correlation function... 

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