Viscodensitometer Studies on Gelatine and the Sorption of Gelatine on Glass

Abstract

The sorption of polymers on glass surfaces, and the effects produced thereby on measurements of intrinsic viscosity, hitherto studied in capillary viscometers, is here analyzed by the sensitive viscodensitometric technique, based on the principle of the moving-sphere viscometer. By working with several spheres of equal size, the errors in viscometry due to sorption can be practically eliminated. The use of two spheres differing in radius by a factor of 10 allows the direct weighing of the polymer sorbed per unit geometric surface. In this way the sorption isotherm of an alkali-bone gelatin on Pyrex glass from 0.17 M KCl solution was found to rise to a plateau of 3 mg/m² at a gelatin concentration of 0.1 g/dl. The plateau extends from this lower limit to 0.5 g/dl. The partial specific volume of gelatin, directly obtained in the viscodensitometer along with the viscosity, was found to be 0.702 cc/g in water and 0.725 cc/g in 0.95 M KCl.