Effect of shear on the apparent viscosity of amorphous carbonate ion containing aluminum hydroxide suspensions

The application of shear to carbonate ion containing aluminum hydroxide suspensions caused a change in the apparent viscosity by two possible mechanisms: change in the surface charge because of desorption of specifically adsorbed carbonate ion, and aggregate dispersal and formation of more extensive particle networks. The desorption of specifically adsorbed carbonate ion is related to the expansion of the air-liquid interface during shear. Shear-inducing processing equipment which generates a minimal amount of new air-liquid interface was found to produce the least change in pH and, consequently, in surface charge. However, viscosity increases caused by aggregate dispersal and formation of more extensive particle networks may occur without a shear-induced change in surface charge.     

In Vitro Adsorption of Bile Salts by Colestipol Hydrochloride

The acid–base titration of colestipol hydrochloride exhibits no sharp inflection points, indicating a weakly basic anion-exchange copolymer. The swelling of colestipol hydrochloride in water and the adsorption of cholate anion are inversely related to pH and are, therefore, related to the ionization state of the copolymer. The Langmuir adsorption parameters at pH 7.5 and 37°C are similar for cholate, glycocholate, and taurocholate anions. Adsorption capacity was not related to particle size and exceeded the adsorptive capacity of the external surface by three orders of magnitude. Therefore, it is believed that the swelling of colestipol hydrochloride makes extensive internal surface area available for adsorption of bile salts. The rate of adsorption depends on the concentration of sodium cholate to which the colestipol hydrochloride is exposed. Adsorption was complete within 5 min when the concentration was below the adsorptive capacity. In contrast, adsorption at levels of sodium cholate at or above the adsorptive capacity was not complete within a 3-hr test period.