Masayasu Tasaka

Concentration dependence of electroosmosis and streaming potential across charged membranes

Abstract Electroosmosis and streaming potential measurements were carried out across charged membranes made of collodion and sulfonated polystyrene. Experiments were confined to the range where linear flux/force relationships hold. Saxens relationship holds between electroosmosis and streaming potential; for porous charged membranes these exhibit an approximate inverse proportionality to ionic mobility at the limit of low electrolyte concentration. Both tend towards zero at the limit of high electrolyte concentration.

Solvent transport across anion-exchange membranes under a temperature difference and an osmotic pressure difference

Abstract Solvent transport across anion-exchange membranes was measured for water and aqueous KCl, KF, KIO 3 , KClO 3 , HCOONa, CH 3 COOK, C 2 H 5 COONa, C 6 H 5 COONa, C 6 H 5 SO 3 Na solutions under a temperature difference and an osmotic pressure difference. Anion-exchange membranes Neosepta® AFN and modified porous AFN(P) were used. The porous membrane AFN(P) was prepared by treating Neosepta® AFN with NaOH solution. Plots of the volume flux against the temperature difference between the solutions on both sides give straight lines starting from zero. The direction of thermoosmosis was from the cold side to the hot side. Solvent transport across anion-exchange membranes under a temperature difference and an osmotic pressure difference is proportional to the water content of the membranes that is represented by the weight of absorbed water per one gram of dry membrane matrix without counterions, and is almost independent of the counterion species.

Mass transfer through polymer membranes due to a temperature gradient

Abstract Water transfer through various hydrophilic and hydrophobic polymer membranes was observed under a temperature gradient and analyzed by a theory based on nonequilibrium thermodynamics. Water is transferred through hydrophilic polymer membranes from the cold side to the hot side because the transported entropy of water in the membrane is smaller than the molar entropy of water in the external free solutions. In contrast, water is transferred through hydrophobic polymer membranes from the hot side to the cold side because the transported entropy of water in the membrane is larger than the molar entropy of water in the external free solutions.

Freezing and nonfreezing water in charged membranes

Abstract Freezing and nonfreezing water contents in perfluorosulfonated membranes and sulfonated hydrocarbon membranes were estimated using differential scanning calorimetry. In the sulfonated hydrocarbon membranes the amount of freezing water decreased with the increase of divinylbenzene content and with the decrease of water content. When the molalities of fixed charges in sulfonated hydrocarbon membranes and perfluorosulfonated membranes were similar to each other, the free water content in the perfluorosulfonated membranes was larger than that in the sulfonated hydrocarbon membranes. The number of moles of nonfreezing water per mole of fixed charges in the perfluorosulfonated membranes was smaller than that in the sulfonated hydrocarbon membranes.

Dependence of bi-ionic potential across membranes on salt concentration

Abstract Measurements of bi-ionic potential across four porous cation-exchange membranes, a porous anion-exchange membrane, and a nitrobenzene liquid membrane for KCl/NaCl and KCl/LiCl systems were carried out and the experimental data were analyzed by a theory based on non-equilibrium thermodynamics. For porous charged membranes the value of bi-ionic potential depends on the diffusion potential in the membrane phase. That is, the change of bi-ionic potential is based on the change in the concentration of co-ions in the membrane phase. However, Donnan potentials at the two solution/membrane interfaces compensate each other and are negligible compared with the total membrane potential. For the nitrobenzene membrane, the value of bi-ionic potential varies largely with the electrolyte concentration even though the transport number of the counterions in the membrane is nearly unity. The behavior of the concentration dependence of the bi-ionic potential across the nitrobenzene membrane is markedly different from that across porous charged membranes.

Thermoosmosis through charged membranes. theoretical analysis of concentration dependence

A theoretical equation for thermoosmosis through charged membranes in electrolyte solutions is derived from nonequilibrium thermodynamics. The theory shows that the volume flux through the membrane is proportional to the temperature difference across the membrane. The proportionality constant, i.e., the thermoosmotic coefficient is a function of electrolyte concentration. The electrolyte concentration dependence of the thermoosmotic coefficient calculated is compared with our previous experimental results. Agreement between theory and experiments is satisfactory.

Thermal membrane potential across anion-exchange membranes in KCl and KIO3 solutions and the transported entropy of ions

New simple thermal membrane potential cells with a solution inlet channel were constructed from two blocks of poly(methyl methacrylate) resin. Using these cells the thermal membrane potentials across anion-exchange membranes Aciplex® A-201 and A-211, Neosepta® AM-1 were observed in KCl and KIO3 solution systems. It is easier to handle the new cells because of the simple cell construction compared with the cells with a solution inlet nozzle used up till now. The thermal potentials measured with the new cells were similar to those obtained with the old ones. The thermal membrane potential Δψ across the anion-exchange membranes was always positive at the cold solution side. The temperature coefficient of the thermal membrane potential per unit temperature difference Δψ/ΔT is proportional to the logarithm of the activities of the ions and the slope of this plot was R/F in the range of ideal permselectivity for counterions as expected from the previously presented theory. The transported entropies of the counterions in the membrane were estimated by combining data for the thermal membrane potential, thermoosmosis and electroosmosis. It is shown that the contribution of the water term to the thermal membrane potential as well as to the concentration membrane potential plays an important role.

Anomalous osmosis and salt concentration dependence of the reflection coefficient in charged membranes

Rates of permeation of water and electrolytes through an anion exchange membrane, prepared by the adsorption of a polycation on preformed collodion membrane, were measured. The experimental results are in agreement with a theory presented previously. An equation for the salt-concentration dependence of the reflection coefficient was derived and compared with both the theory of Kedem and Katchalsky and the experimental data. The agreement between the two theories and experiments is good. It is shown quantitatively that the total entropy production in negative osmosis is positive, because the absolute value of the entropy production due to solute is very much larger than that due to water.

Thermoosmosis through charged membranes

Thermoosmosis through oxidized collodion and collodion-sulfonated polystyrene interpolyrene interpolymer membranes has been observed in KCl solutions of various concentrations. The effective temperature difference acting for thermoosmosis was determined by measuring the thermal membrane potential appearing on both sides of membrane. It was found that the velocity of thermoosmosis is proportional to the effective temperature difference and the proprtionality constant (themoosmotic coefficient) is a function of electrolyte concentration. The dependence of the thermoosmotic coefficient of charged membranes on the electrolyte concentration is found to have a characteristic feature.

Thermal membrane potential through charged membranes in electrolyte solutions

Measurements of the thermal membrane potential across cation and anion exchange membranes were carried out by using the same solution of various 1-1 electrolytes on both sides of the membrane. In all cases a good linear relationship was observed between the thermal membrane potential increment psi and the temperature difference increment T. The slope of the linear plot varied with the concentration of the electrolyte. The value of increment psi/increment T versus logarithmic activity of the electrolyte plot was linear with a slope of +/- R/F if the transport number of counterion was unity. The magnitude of increment psi/increment T was independent of coion species but dependent on counterions. These experimental results are in agreement with a theory presented previously. The thermal membrane potential caused by the direct effect of temperature differences and that by the indirect effect arising from the changes in ionic and water chemical potentials due to the temperature difference are separately discussed.