Diaphragm Cell Technique Research Articles

Diffusion of Lysozyme in Buffered Salt Solutions

The diaphragm cell technique was used to measure the diffusion coefficient of lysozyme in buffered solutions with and without NaCl. In the absence of salt, the pseudobinary diffusion coefficient decreases with increasing lysozyme concentration. In the presence of NaCl, the main term D11 decreased slowly with increasing NaCl concentrations and exceeded the pseudobinary values by 4–10%. The main term D22 did not vary significantly with NaCl concentration and was slightly less than the binary diffusion coefficient for NaCl. The cross-term D21 increased sharply with salt concentration. The cross-term D12 is small and decreased slowly with salt concentration. These results are consistent with the expected electrostatic interactions between lysozyme and salt in the diffusion process.

Starch based hydrogel with potential biomedical application as artificial skin

Hydrogel wound dressing can protect injured skin and keep the woundsurface appropriately moist to speed the healing process by absorbingexudates while maintaining the products of tissue repair, including growthfactor and lysosomes, in contact with the wound. The design anddevelopment of novel membrane of hydrogel prepared by crosslinking ofpolyvinyl alcohol with starch suspension using glutaraldehyde as acrosslinking agent was attempted. The membrane was characterized byFTIR spectroscopy. The mechanical property of the hydrogel membranewas characterized by tensile tests. The diffusion coefficient of salicylic acidthrough the membrane was also evaluated using diaphragm celltechnique. FTIR spectra of the membrane indicated the absence of freealdehydic groups of glutaraldehyde. The membrane had sufficient strengthto be used as artificial skin. At 30 °C, the measured value of the diffusioncoefficient of salicylic acid was approximately 4.11×10- 6 cm2/s.(Afr. J. Biomed. Res. 9:23 – 29, 2006)Keywords: Wound Healing; Hydrogels; Crosslinking; Polyvinyl Alcohol; Starch

Diffusion coefficient of paracetamol in a chitosan hydrogel

The diffusion coefficient of the analgesic drug paracetamol (acetaminophen) in macroporous chitosan hydrogels has been measured using a diaphragm cell technique. The pore structure in the hydrogel was varied by changing the amount of chitosan added to the aqueous solution. At 37 °C, the measured values of the diffusion coefficient are between 0.1 and 5×10 −8 m 2/s depending on the macropore size in the hydrogel. The diffusivity increases with temperature and the activation energy has been estimated to be on the order of 25 to 30 kJ/mole. The data indicate that solute transport through the gel occurs primarily by Fickian diffusion.

Diffusion coefficients for HCl and HBr in 30 wt % to 72 wt % sulfuric acid at temperatures between 220 and 300 K

Diffusion in sulfuric acid plays a role in heterogeneous stratospheric processes. Knowledge of diffusion coefficients is required to determine the partitioning of heterogeneous reactions between the bulk and the surface of sulfate aerosol particles. Diffusion coefficients are also needed to analyze time‐dependent uptake data to obtain solubilities. In order to provide quantitatively accurate diffusion coefficients, the experimental challenges of measuring solute diffusion in strong electrolyte environments must be overcome. We use a modified diaphragm cell technique and report diffusion coefficients for HCl and HBr in sulfuric acid solutions from 220 to 300 K. We find that the temperature and viscosity dependence of these measurements follows the equation D = cT/η, where η is viscosity, yielding c = 7.8 × 10−8 cm2 cP/s K for HCl and c = 7.9 × 10−8 cm2 cP/s K for HBr. An empirical equation for predicting diffusion coefficients for other species in sulfuric acid is also presented.

Tracer Diffusion of Water in Organic Liquids

The tracer diffusion coefficient, Dw, for water (as HTO) in 28 organic solvents, including 13 esters, benzene, and 7 substituted benzenes, has been determined at 298.15 K using the diaphragm cell technique. The variation of the water diffusion coefficient with solvent viscosity (η) is significantly different for the hydrophobic solvents (benzene and substituted benzenes, cyclohexane, hexane, and tetrachloromethane) in comparison with the other solvents, in that the Dwη product is significantly larger (average value 3.68 × 10-12 N compared to 1.60 × 10-12 N). The apparent hydrodynamic radius derived from the Stokes−Einstein equation is about half the molecular radius for water diffusing in the hydrophobic solvents, and 1−1.5 times the molecular radius for diffusion in the other solvents.

Intradiffusion coefficients for perchlorate ions in zinc perchlorate and zinc chloride solutions at 25�C: Comparing transport properties of zinc chloride and zinc perchlorate systems

Intradiffusion coefficients for36ClO4− have been measured in solutions of zinc perchlorate of concentration 0.1 to 3 mol dm−3 at 25°C by the diaphragm cell technique. In addition, intradiffusion coefficients for perchlorate ions in zinc chloride solutions have been measured over a concentration range at 25°C. The results confirm previous work on the effect of complexation on diffusion in zinc chloride solutions above a salt concentration of 0.1M. The present data, together with literature data for diffusion coefficients of the other species present in the zinc perchlorate electrolyte system, have enabled a simple analysis of the hydration around the zinc ions to be carried out. This indicates that the water diffusion data are consistent with the zinc ions having an effective hydration sphere of 11 (±2) water molecules. This is in keeping with values obtained for other simple divalent electrolytes using the same model. The model is extended here to allow analysis of water diffusion in zinc chloride solutions taking into account the presence of complexed chloro-zinc species. The experimental data are consistent with the effective hydration of the chloro-zinc complexes being independent of the number of chloride ligands and equal to 18±3 over a concentration range of 0 tol mol-dm−3. This postulate is discussed in terms of its consequences on the water ligand dynamics for the complex equilibria.

High-Temperature, Aqueous-Phase Diffusion of NaCl through Simulated Deposits of Corrosion Products

Abstract Aqueous-phase effective diffusion coefficients were measured for sodium chloride in simulated porous corrosion products using a modified diaphragm cell technique at temperatures from 25°C to 280°C. The effect of the pore structure on the measured diffusion coefficient was determined from the bulk diffusion coefficient at the experimental temperature. A tortuosity factor was calculated for each corrosion product as a function of temperature. The tortuosity factor was used with a bulk diffusion coefficient and porosity to estimate the transport rate of a solute specie in corrosion products at elevated temperatures and pressure.

Tracer diffusion in aqueous sucrose and urea solutions

Tracer diffusion coefficients for water (as HTO), methanol (14CH3OH), and acetonitrile (CT3CN) in aqueous sucrose (10–25% w/w) and urea (0.25–4 mol L−1) solutions at 298 K have been determined using the diaphragm cell technique. For sucrose solutions tracer diffusion coefficients vary with the 2/3 power of the relative viscosity and the viscosity dependence is the same for the above tracers as for sucrose and oxygen. In urea solutions tracer diffusion coefficients appear to have a solute-specific viscosity dependence, but the solute specificity is largely removed when the effects of proton exchange and urea dimerisation are considered. Keywords: diffusion, water, methanol, acetonitrile, sucrose, urea.

The effect of concentration and temperature on diffusivity of metal compounds

The effect of concentration and temperature on diffusivity of various metal compounds which are frequently used in hydrometallurgical applications has been investigated. A diaphragm cell technique has been adopted in this study. Diffusivity of cobalt, nickel, copper, and iron compounds was measured in water with and without ammonia. The effect of chloride, nitrate, and sulfate on diffusivity of these metals in the above-mentioned solutions was studied. The effect of cyanide concentration on diffusivity of gold, silver, copper, and iron in solution was also investigated. The range of the concentration of solutions used in this study was 10-4 to 0.5 M. Temperature was varied between 15 °C and 45 °C. An empirical model for metal chloride, nitrate, and sulfate systems has been developed to predict diffusivity of various metal compounds when concentration, charge, size, and mobility of diffusing species are known. The predicted values of diffusivity of numerous metal compounds by this model are in good agreement with the observed values for the ionic strength less than 0.5 M.

Metal Ionic Diffusivity: Measurement and Application

Diffusivity of metal compounds in aqueous solutions is a very important parameter in hydrometallurgical processes. In metal extraction using a hydrometallurgical method or in the case of solvent extraction, diffusion of metal ions through various medium frequently plays a controlling role. Therefore, correct information on diffusivity of the relevant species is necessary in order to understand the mechanism of the unit process in question. In this paper, various techniques used in measurement of diffusivity of metal compounds in solution are reviewed. A detailed discussion on the practical applicability of the diaphragm cell technique is given, since this technique is regarded as an easy and reliable technique in measuring diffusivity of species dissolved in aqueous media. Also reviewed are theoretical approaches to diffusivity in aqueous media.

Association of caffeine in aqueous solution. Effects on caffeine intradiffusion

Tracer-(intra-) diffusion coefficients of 14C-labelled caffeine, DT, have been measured by the diaphragm-cell technique over the temperature range 37–80 °C and as a function of concentration to a maximum of 0.29 mol kg–1 at 50 °C, extending earlier measurements at 25 °C. Limiting mutual diffusion coefficients, D∞, have also been determined with the Taylor dispersion technique between 20 and 65 °C. The concentration dependence of the relative intradiffusion coefficients changes little above 37 °C, but is stronger at lower temperatures. The results are analysed with the aid of association models.

Diffusivity of cobalt and nickel compounds as a function of concentration and temperature

Diffusivity of cobalt and nickel compounds has been measured using a diaphragm cell technique. Diffusivity of these metal compounds including chloride, nitrate, and sulfate was measured over the concentration range of 0.005 to 0.5 M. A correlation equation for diffusivity of cobalt and nickel compounds has been established:D = 2.0 × 10−5(z ·r)−0.2 C −n, whereD: diffusivity, cm2/s; z: valence of anion;r: radius of hydrated metal compound; C: molar concentration of electrolytes; andn: 0.0497 for cobalt and 0.025 for nickel. The effect of temperature on the diffusivity of cobalt and nickel compounds was also studied. Arrhenius activation energy values of diffusion for cobalt and nickel compounds were found to be 14.7 to 18.0 kJ/mol.

Chemistry of eutectic and monotectic; phenanthrene-succinonitrile system

The solidification behavior of the phenanthrene-usccinonitrile system was studied by measuring the growth rates of the moving front and the microstructures of the parent components and different mixtures. The phase diagram was experimentally determined by the thaw-melt method. A eutectic (0.975 mole fraction of SCN) and a monotectic (0.225 mole fraction of SCN) were observed with a liquid miscibility gap in the system. The experimental value of the diffusion coefficient determined by the diaphragm cell technique is 0.95 × 10 -5 cm 2/ s. The experimental data were analysed using the current theories of solidification behavior of eutectics and monotectics. λ 2 v was found to be much higher for the monotectic than for the eutectic, where λ is the spacing and v the growth velocity. The enthalpy of mixing was determined experimentally to throw light on the position and structure of the liquid eutectic. The very high value of the enthalpy of mixing confirms the immiscibility in the liquid and the position of the eutectic far away from the equicomposition. Phase separation was studied in the region of immiscibility by analysing the composition of the solidified column. Ph clearly separates leaving SCN on the upper portion of the column.

Isothermal diffusion coefficients of aqueous alkyl carboxylates

Porous diaphragm cell technique has been followed for the measurements of diffusion coefficients of some aqueous aliphatic alkyl carboxylates, by using the solution-filled methodology. The results are discussed in terms of classical hydrodynamic treatments as well as the relative magnitudes of “obstruction” and local “structure-breaking” effects of the solutes.

Diffusion in Liquid Mixtures of Light and Heavy Water

AbstractWith the aid of the diaphragm cell technique tracer diffusion of tritium‐labelled water in H2O—D2O mixtures has been measured at 8, 25 and 45°C. In addition, self‐diffusion coefficients in H2O—D2O mixtures have been determined by the proton n.m.r. spin‐echo technique. Paralleling the behaviour of the mutual diffusion coefficient, the tracer diffusion coefficients exhibit small negative departures from a linear concentration dependence which usually is predicted for diffusion in ideal systems.

Diffusion coefficients of aqueous cesium fluoride at 40°C

Diaphragm cell technique has been employed to determine diffusion coefficient for cesium fluoride at 40°C in the concentration range varying from 0.01 to 0.1 M. The data were analysed in the light of the theory of Onsager and Fuoss (O-F), J. chem. Phys. 2, 599 (1932)[20]. The results indicate that the O-F theory is inadequate to explain the behaviour of this salt at 45°C. The results are also discussed with other 1:1 type salts of cesium.

Transport in aqueous solutions of Group IIB metal salts. Part 7.—Measurement and prediction of isotopic diffusion coefficients for iodide in solutions of cadmium iodide

Isotopic diffusion coefficients for iodide have been measured in aqueous solutions of cadmium iodide over the concentration range 0.1–1.0 mol dm–3, using the diaphragm cell technique. The iodide diffusion coefficients are shown to decrease smoothly but steeply from the infinite dilution value of 2.046 × 10–5 cm2 s–1 to less than half that value in the concentration range above 0.1 mol dm–3. This remarkable decline has been assigned to the presence of complexes of the type CdI+2–xx(x= 1, 2, 3, 4). The irreversible thermodynamic analysis developed previously for cadmium diffusion in this same system (part 4) has been extended to include isotopic diffusion of labelled ligands on multiply substituted complexes. Using this analysis the observed iodide diffusion coefficients have been predicted within close limits over the whole concentration range up to ≈ 0.5 mol dm–3.

Diffusion in organic liquids. Part 1.—Appraisal of a gel sectioning technique and its application to self-diffusion in benzene and cyclohexane

A novel gel sectioning technique has been devised for the assessment of self-diffusion coefficients in organic liquids. Its application to benzene and cyclohexane yields results for both diffusion coefficients and their temperature-dependence which are in excellent agreement with values obtained with the conventional diaphragm cell technique.

Self-diffusion coefficients of water in pure water and in aqueous solutions of several electrolytes with 18O and 2H as tracers

The self-diffusion coefficients of water in pure water and in aqueous electrolyte solutions have been measured by using the sintered glass diaphragm cell technique with 2H and 18O as tracers. The extrapolated value from 2H tracer data, 2.27 × 10–9 m2 s–1, agrees with the value from 18O tracer data which is less sensitive to tracer concentration. In most electrolyte solutions investigated, no significant isotope effect in water diffusion was observed.

Transport in aqueous solutions of group IIB metal salts (298.15 K). Part 3.—Isotopic diffusion coefficients for cadmium-115 ions in aqueous cadmium iodide

Cadmium isotopic diffusion coefficients (Daa) were determined in aqueous cadmium iodide in the concentration range 0.1–0.6 mol dm–3. Daa passes through two maxima, one below 0.1 mol dm–3, the other at 0.4 mol dm–3. Irreversible thermodynamic analysis shows that these maxima are due to positive fluctuations in the isotope-to-isotope coupling contributions to Daa. For these studies a modified diaphragm cell technique was developed.