Diffusion Coefficient Of Sodium Ions Research Articles

Reverse permeation of sodium ions driven by pH difference across a liquid membrane: time dependencies of membrane resistance and membrane potential in a reverse permeation system

The diffusional flux of sodium ions across a liquid membrane was observed as a reverse permeation phenomenon: sodium ions were transported across the membrane against their own concentration difference. A supported liquid membrane having stearic acid as an ionic carrier was used. The internal aqueous phase contained NaCl and HCl and the external aqueous phase contained NaOH of the same initial concentration as NaCl in the internal aqueous phase. The reverse permeation occurred with a long time delay. During the delay, sodium ions flowed from the acidic to alkaline solution. The diffusion coefficient of sodium ion estimated from the flux equation taking into account the Donnan equilibrium at the interface was found to be much greater than that in the membrane solvent, 1-octanol. In the same membrane system as for the flux measurement, the membrane conductance and the membrane potential were measured as a function of time. The time dependence of the membrane potential in the presteady state showed a biphasic behavior. The initial rapid phase could be attributed to the change in the phase boundary potential and the subsequent slow step to the change in the diffusion potential within the membrane. Before the steady membrane potential had been reached, the reverse permeation of sodium ions against their own concentration difference was not observed. During the slow relaxation process of the membrane potential, the membrane resistance decreased to approach the steady state. Moreover, the oscillation of membrane potential abruptly started at a time in the slow step of the potential change and continued during the steady state. It was suggested that, at the presteady state, the increase in the amount of water in the membrane would drive a drastic change in the state of the liquid membrane in the filter pore, e.g. an inverted micellar structure making.

Ionic and Chain Interdiffusion and Interfacial Strength Development in Ionomers of Poly(ethylene-co-methacrylic acid)

Diffusion coefficients of sodium and zinc ions have been measured in bilayers of commercial, partially neutralized poly(ethylene-co-methacrylic acid). The diffusion behavior shows a break at the melting temperature of the resin, suggesting that chain backbone motion is intimately related to ionic transport. The ionic diffusion coefficients are orders of magnitude greater than those of the chain backbone, which suggests that metal ion pairs are transported along the contour of the polymer network via exchange with protons of neighboring acid groups. Interfacial strength development in welded films of ionomers is primarily determined by the melting behavior of the bulk resin. Ionic diffusion rates do not correlate with the strength development behavior. This observation, along with melting and chain center of mass diffusion information, suggests that strength development is dependent on chain interdiffusion like that of many other thermoplastics.

Electrochemical alkali metal intercalation into (BiS) 1.17(NbS 2) 2

Lithium and sodium electrochemical intercalation into the (BiS) 1.17(NbS 2) 2 misfit layer compound was studied in A/ AClO 4(PC)/sulfide cells (A=Li, Na). The periodic length of the original compound (17.385 Å) is consistent with an NbS 2 NbS 2BiS stacking sequence. This parameter increased by about 0.33 and 0.78 Å after 1 F/mol discharges of Li and Na cells, respectively. For both alkali metals, the potentiostatic discharge curve of the cells showed an initial decrease in voltage followed by subtle changes in the slope of the voltage-composition curve. Current versus voltage curves revealed three diffuse peaks ascribable to lithium ordering in the interlayer space, while a single peak occurred for sodium at about 1.5 V. The chemical diffusion coefficients of Li are consistent with octahedral site occupancy. Na intercalation perturbed the structure heavily as shown by the low diffusion coefficients of sodium ions.

Correlation of Viscosity and Conductance with 23Na+ NMR T1 Measurements

Abstract The relationship between rotational correlation time and the translational diffusion coefficient (Stokes–Einstein equation) of sodium ions dissolved in a series of water–glycerol solutions was studied. NMR longitudinal relaxation measurements gave an estimate of the rotational correlation time for the hydrated sodium ion. From this, using the Debye and Stokes–Einstein equations the translational diffusion coefficient was calculated. These results were compared with estimates of the sodium ion diffusion coefficient obtained using pulsed field gradient NMR. The simple, chemical system was chosen for this study so that the nature of the sodium relaxation would be unambiguous. Also, conductivity measurements were performed on each solution since the conductivity is intimately related to the rate of ionic diffusion. The results showed that due to the spherical nature of the hydrated sodium ion the Debye and Stokes–Einstein equations are well obeyed allowing translational diffusion coefficients to be calculated from rotational correlation times in good agreement with those measured using pulsed field gradient NMR.

Membrane potential and permeability of charged cellulosic membrane in aqueous alkali metal salts systems.

The membrane potential and permeability of charged cellulosic membrane in alkaline metal salts solution were determined at 25°C. The membranes used were carboxyethyl cellulose (CEC), sulphoethyl cellulose (SEC) and phosphorylated cellulose (PC) with the same degree of substitutions. The membrane potential and permeability as a function of the salt concentration were analysed by means of TMS theory.In a series of alkali metal chlorides the diffusion coefficients of cations in membranes decrease with increasing Stokes radius of the cations. On the other hand the diffusion coefficients of chloride anion which is the common counterion species increase with increasing Stokes radius of the cations. In the case of sodium salts carrying different counter anion, i.e., NaCI, NaNO3, and C6H5SO3Na, the larger the ionic sizes the diffusion coefficients of anion decrease. While the diffusion coefficients of sodium ions in these salts are approximately the same value.The effective fixed charge density and the diffusion coefficient of ions in the membranes increase in a sequence of CEC<SEC≤PC membranes. These results are explained by considering the counterion binding by the negatively charged groups in the membranes.

Estimation of sodium chloride diffusion coefficient in gastric mucin.

Estimates of the diffusion coefficient of hydrogen and sodium ions were made in solutions of artificial porcine mucin. When stirred compartmental systems were used, the calculated diffusion coefficients were one order of magnitude higher than free solution values, if the contribution from the support membranes was evaluated. It is likely that the stirred systems induce forced convection in a central compartment, leading to overestimation of path length and consequently erroneous values for the diffusion coefficients. In these systems, mucus probably only reduces the forced convection and increases the apparent path length. In a static diffusion cell, mucus reduced the diffusion coefficient for sodium ion significantly. No attempt was made to estimate DH+ because of the compromising effect of buffering by the mucus. The reduction in DNa+ depended on the concentration of mucin used but was not pH dependent. The calculated activation energy indicated factors other than steric hindrance to be involved in the restriction of free diffusion in mucus solutions.

Effect of Water Content on the Electrical Conductivity of Na2O≅3SiO2 Glass

Na2O–3SiO2 glasses with up to ≅12 wt% water were prepared under high‐pressure, hydrothermal conditions and their electrical conductivities were measured. The conductivity (σ) was found to depend on H2O content in a manner similar to the “mixed‐alkali” effect. At constant temperature, σ decreased initially with increasing H2O content to a minimum at 3≅4 wt% H2O and increased with further increase in water content. Infrared spectroanalysis of these glasses was made to determine the type of water present in the glass and the results were interpreted in the context of the measured activation energy and preexponential factor of dc conductivity. The sodium ion diffusion coefficient for a glass containing 0.76 wt% H2O was less than that of water‐free glass and in agreement with the electrical conductivity results.

Translational motion and association in aqueous sodium cholate solutions

Self-association in aqueous sodium cholate solutions was studied at 25°C by determining the translational self-diffusion coefficients of water molecules, cholate ions, and sodium ions. Association was found to be much more gradual than for simple surfactants. Thus association starts at a concentration of about 0.014 mole/kg and progresses continuously up to the highest concentrations studied (0.5 mole/kg). The counterion association degree, which was derived from the sodium ion diffusion coefficient, is much lower than for typical micelle-forming substances. From the concentration dependence of the water self-diffusion coefficient the micellar hydration number was estimated. Hydration was found to be much more extensive than for simple surfactant micelles.

Self-diffusion of Sodium Ions in Some Silicate Glasses

Self-diffusion of sodium ions in some silicate glasses was measured by means of RI tracer technique. At the binary system of Na2O-SiO2 glasses, the diffusion coefficient of sodium ions increases exponentially with the increase of this ion concentration. The introduction of Li2O, K2O, CaO and La2O3 into the glass brings about the lowering of diffusion coefficient of sodium ions. The effect of Ca, Al and La ions on the diffusion of sodium ions is explained in terms of the polarizing power of these cations to oxygen electron shell, being similar to the behavior of di-valent ions such as Mg, Sr, Ba, Zn, Cd and Pb. But Li and K ions are considerably different from di-, and tri-valent cations, and the behavior of both ions are probably related to “mixed alkali effect”. The reasons for this effect are not understood at present.The calculation of so-called correlation factors (f) was carried out by the modified Nernst-Einstein equation, and gave the values about 0.2-0.3 for each glass. By analogy with the relation between correlation factor and diffusion mechanism in ionic crystal, it may be supposed from the observed f-value that transport of sodium ions are by some type of vacancy or interstitialcy mechanism. However, such estimation is too simple for glasses having a more complicated structure than ionic crystal.

Ordered Structure and Ion Migration in Silicon Dioxide Films

Structure of silicon dioxide films thermally grown on silicon was studied with electron diffraction and the effect of impurities intentionally added during oxidation was examined. The local polycrystallization of SiO2 films is enhanced by protons or boron atoms. Phosphor, on the contrary, suppresses the crystallization and antimony behaves in a similar way. Gallium has no influence on the phenomenon. Diffusion coefficient of sodium ions in these samples was also measured and activation energy for diffusion was obtained 1.0 to 1.4 eV which coincides well with those reported by other workers. These values are not affected by the presence of impurities or structural anomalies, but the diffusion coefficient itself is large where the crystallization is marked. Phosphor immoblized sodium ions and the diffusion of protons was observed instead. These effects of impurities can be explained considering their valency and sites they occupy in SiO2 network.