N. Lakshminarayanaiah

Studies with composite membranes. II. Measurement of asymmetric properties.

Electrical potentials arising across composite membranes when they separate the same concentration of a (1:1) electrolyte or electrolytes have been measured. These potentials have been shown to arise from differences in the transport number of counterions contacting the two faces of the membrane which contained in its body a high concentration of electrolyte and polyelectrolyte. When the concentration of this trapped electrolyte or polyelectrolyte is low, the asymmetry potentials are small. Although measurements of current-voltage relations provided evidence for the existence of asymmetry between the two faces of the membrane, osmotic flow of water in either direction across the membrane and the salt flow in the two directions were symmetrical. These solvent and solute flux measurements lasted more than 30 hr. Short-term (about 4 hr) flux measurements, however, using tritiated water (THO), gave flows which were different in the two directions. Similarly, the salt flows measured using (22)Na isotope were different in the two directions. The usefulness of the present system as a model to use for studies concerned with carrier transport problems in biology has been pointed out.

Studies with Composite Membranes: I. Preparation and Measurement of Impedances

Simple and composite membranes have been prepared from 2% collodion solutions containing different amounts of polystyrenesulfonic acid (PSSA). Various membrane parameters such as water content, electrolyte uptake, exchange capacity, and permselectivity of these membranes have been determined. The resistance and capacitance of simple membranes have been measured as functions of both external electrolyte concentration and internal fixed charge density. The impedance characteristics of composite membranes also have been determined and discussed in terms of the resistance and capacitance characteristics of simple membranes from which the composite structures have been formed.

Studies with Composite Membranes: III. Measurement of Water Permeability

The permeability of tritiated water (THO) across simple and layer-type composite membranes of collodion containing different amounts of polystyrenesulfonic acid has been measured and corrected for the effects of aqueous stationary layers present at the membrane-solution interfaces. It was found that the water permeabilities in the two opposite directions across the composite membranes were different, whereas they were the same across simple membranes. The theoretical permeability value for the composite membrane (formed by putting one simple membrane on top of another simple membrane of increasing charge density and gently pressing them together), calculated from the values due to simple membranes, was found to be always greater than the two measured values. It was shown that the aqueous layers trapped between membranes were not responsible for the low measured values. The factor causing this was ascribed to the mechanism which produced rectification of water flow in the composite membranes. Establishment of the THO concentration profile in the layered membranes showed that accumulation and depletion of THO in the membrane phase when the THO was flowing from the high charge density side to the low charge density side and vice versa, respectively, were responsible for the unequal flows observed across the composite membrane in the two directions.

Some Asymmetry Properties of Composite Membranes

Composite membranes of two types, layer-type and sandwich-type, have been prepared from 2% collodion solutions containing different amounts of polystyrene sulfonic acid. The layer-type membranes were formed by evaporating first a collodion solution containing the least amount of the polyelectrolyte. On top of this collodion solutions containing increasing quantities of the poly-electrolyte were evaporated one after the other. Sandwich-type membranes were formed by trapping some polyelectrolyte between two simple membranes, one containing a small quantity and the other containing a large quantity of the polyelectrolyte.