Quantitative Treatment of the Variation of some Physico-Chemical Properties of Purified Colloidal Electrolytes with Dilution

Abstract

It is generally assumed that in aqueous solution each particle or macromolecule of the colloidal electrolyte is surrounded by an ion-atmosphere in which the number density of the counterions is greater than that of the co-ions, but the particle or the macro molecule with its ion-atmosphere, as a whole, is electrically neutral and that the thickness of the ion-atmosphere is small compared to the distance between the centres of two neighbouring particles except when the concentration of the colloid is very high. Starting with this simplified picture and assuming further that in a highly purified colloidal solution the thickness of the ion atmosphere and the activities of the (diffusible) ions in the inter micellar solution do not change appreciably with dilution equations have been deduced to account quantitatively for the variation of (1) counter-ion activity, (2) the specific conductivity and (3) the osmotic pressure with the concentration of the colloidal electrolyte. The equations have been subjected to test using the data available in the literature on congo red, cetylsulphonic acid benzopurpurin 4B and its isomer prepared from metatolidine, azarectic (neem gum) acid, gum arabic acid, polyacrylic acids, clay acids and their salts and have been found satisfactory. Furthermore, using the aforesaid expression for the variation of specific conductivity with dilution, Smoluchowski's equation for the electroviscous behaviour of colloids has been modified and equations have been deduced to account for the variation of electro-viscosity of solutions of colloidal electrolytes with dilution. These equations have been subjected to test using the data available in the literature on viscosity of sols of sodium thymus nucleate, gum arabic acid, polyacrylic acids of different degrees of polymerisation, silver iodide, bovine serum albumin. β-lactoglobulin, ribonuclease and mono-disperse polystyrene lattices prepared by emulsion polymerisation using Na-stearate and Na-dodecylsulphate as emulsifiers and have been found satisfactory.