The Structure of the Collodion Membrane and Its Electrical Behavior

Abstract

IPrevious publications 1, ~ in this series have dealt with the preparation and electrochemical properties of the activated (electronegative) collodion membrane. The activation consisted of an oxidation of the nitrocellulose, a process which caused an increase in the number of dissociable groups in the pores of the membrane. Such membranes show more pronounced effects than similar untreated membranes when tested by electrochemical methods such as the extent of anomalous osmosis, the magnitude of concentration potentials, and the rate of electroosmosis. The purpose of the present communication is to present a method for the preparation and a description of electropositive membranes which are analogous in most respects to the activated collodion membranes.The literature on electropositive membranes has recently been reviewed by Manegold and Kalauch? Two general methods for the preparation of such membranes are available. First, they have been prepared from inherently electropositive materials, such as the oxides of aluminum, zirconium, or thorium.4, s The second method consists of'impregnating membranes prepared from collodion or similar materials with some basic organic compound.One objection to the use of the polyvalent metal oxide membranes is that the electropositive charge is rather easily reversed in the presence of many electrolytes. For this reason they are not suitable for most purposes.The impregnated membrane, in many instances, has proven more practical. The impregnation of collodion with basic substances may be accomplished either by dissolving such substance in the collodion solution or by adsorbing the material on the surface of a previously cast membrane.

Ion Separation by Hyperfiltration Through Charged Membranes. II. Separation Performance of Collodion-Polybase Membranes.

“…Collodion Membranes. The collodion casting solution was prepared according to Sollner's procedure (Abrams and Sollner, 1943). The solution contained 48% ethanol, 50% ethyl ether, 2% water, and either 3 or 5% collodion.…”

“…The first semipermeable membranes carrying charged groups, predecessors of the currently used ion-exchange membranes, were prepared by adsorption of proteins or synthetic polyelectrolytes into porous collodion membranes (Abrams and Sollner, 1943). The adsorption is reversible; the polyelectrolytes are slowly washed out in contact with aqueous solutions.…”

The Effects Produced by Diffusion in Aqueous Systems Containing Membranes.

“…The bound ions may be adsorbed on the surface of the pores, or they may be chemically combined with the substance of the membrane. An example of the first type is provided by the positively charged permselective membranes of Sollner (1,39). These membranes are made by the adsorption of protamine cations on nitrocellulose membranes.…”

“…The diffusion of molecules in solution is described mathematically by Tick's law: dQ/dt = DA dc/dx (1) where Q is the quantity of material which crosses a plane of constant concentration c and area A per unit of time t. D is a proportionality factor, called the diffusion coefficient. As given, Pick's law is just a definition which is useful only because the proportionality factor D is, in many cases, nearly independent of concentration.…”

The Physical Chemistry of Membranes with Particular Reference to the Electrical Behavior of Membranes of Porous Character. I. The Nature of Physicochemical Membranes—Membranes as Physicochemical Machines; Preparation and Properties of Membranes of Highly Pronouned Electrical Properties

“…In all these instances the membrances were what is called conventionally "semipermeable. "2 Pfeffer's membranes were impermeable to the solute sugar 1 Presented in abstract before the Division of Colloid Chemistry at the lOSth Meeting of the American Chemical Society, New York City, September 14, 1944. 2 The term "semipermeable" is used today in a sense wider than the literal meaning of the word.…”