Influence Of Solution Concentration Research Articles

Factors Which Affect the Permselectivity of Nafion® Membranes in Chlor‐Alkali Electrolysis, I

The membrane permselectivities of several bilayer perfluorinated ionomer chlor‐alkali membranes have been measured using a sodium ion radiotracer method with an automated laboratory electrolysis cell. The influence of solution concentrations, electrode‐membrane gap, and solution mixing were evaluated for membranes which differed with regard to fabric reinforcement and surface smoothness. Results indicate that these cell and membrane‐related factors all influence membrane permselectivity in an operating cell, with certain practical consequences. The underlying reasons for this complex behavior are discussed.

Lithia distribution in infiltrated silica gels

Silica gels were prepared by mixing colloidal silica with potassium silicate in a 1:9 weight ratio. Following ion exchange to remove Na and K, the highly porous samples were soaked in methanolic LiOH or aqueous LiNO 3 solutions. The influence of the soaking time was determined for LiOH solutions. The influence of solution concentration was determined for LiNO 3 solutions. Bulk concentrations of Li were increased by increasing the soaking time in LiOH solutions and increasing the solution concentration in LiNO 3 solutions. Once bulk compositions of about 15 mol% Li 2O-85 mol% SiO 2 were achieved, the distribution of Li in the sample was evaluated by dissolving the samples in HF. In all cases, the distribution of Li in the dried samples was not uniform. The Li content was negligible in the middle of the sample. Only in the case of LiNO 3 samples was the chemical uniformity improved by heat treatment at 200°C for 1 h.

Dialysis experiments with asymmetric cellulose acetate membranes

Cellulose acetate membranes for ultrafiltration produced by phase inversion have an asymmetric structure in the cross-section. In spite of this assymetry it is possible to characterize such membranes by dialysis. The asymmetry has no influence on the permeability for solute poly(oxyethylene). The membrane structure was varied systematically by annealing. The influence of solution concentration, dialysis time and temperature was also investigated. Statements are made on the annealing influence. A relationship between diffusion permeability and the true rejection is discussed.

Adsorption-entanglement layers in flowing high molecular weight polymer solutions III: Solution concentration and solvent power

Adsorption entanglement layers are thick, i. e. multimolecular layers formed at solid surfaces during the flow of high molecular weight polymer solutions. The present publication is concerned with the influence of solution concentration and solvent power on the formation of these layers. Three polymers have been used, polyethylene, polymethylmethacrylate and atactic polystyrene in various solvents. The formation and thickness of layers were monitored from their effect on flow behaviour. Two flow geometries were used: Couette flow — where the layers cause peaks in the shear stress during continuous shearing, and capillary flow where the layers reduce the flow rate. The results indicate that there is a critical concentration below which no layers form, and that this critical concentration is an order of magnitude less than the conventionally defined overlap concentration. It is also deduced that the layers form more quickly, and grow to be thicker when better solvents are used.

Concentration effects in the hydrodynamic properties of deoxyribonucleic acid

The influence of solute concentration on measurements of the viscosity and sedimentation properties of DNA solutions is very great. Enough data has been accumulated in recent years, however, to permit a quantitative description of these concentration effects for DNA samples of molecular weight below roughly 16·106. It has therefore become possible to measure [η] and s0 (and indirectly molecular weight) for such samples from single measurements on generally available equipment. Above molecular weight 16·106 the possibility of such a simplification is at present excluded by the magnitude of the concentration effect in sedimentation and the gradient effect in viscosity, plus the newly studied phenomenon of speed dependence in sedimentation. It is shown, however, that rotor speed does not influence the sedimentation of samples up to molecular weight 16·106 until a critical high velocity is reached.

Concentration effects in the hydrodynamic properties of deoxyribonucleic acid

The influence of solute concentration on measurements of the viscosity and sedimentation properties of DNA solutions is very great. Enough data has been accumulated in recent years, however, to permit a quantitative description of these concentration effects for DNA samples of molecular weight below roughly 16·10 6. It has therefore become possible to measure [η] and s 0 (and indirectly molecular weight) for such samples from single measurements on generally available equipment. Above molecular weight 16·10 6 the possibility of such a simplification is at present excluded by the magnitude of the concentration effect in sedimentation and the gradient effect in viscosity, plus the newly studied phenomenon of speed dependence in sedimentation. It is shown, however, that rotor speed does not influence the sedimentation of samples up to molecular weight 16·10 6 until a critical high velocity is reached.