Comparison of Several Diffusion Equations in the Calculation of Viscosity and its Relation to Dissolution Rate

Abstract

The viscosity of polymeric solutions as measured by a rotational viscometer may not be the viscosity of the environment through which a solute molecule diffuses. By use of the Stokes-Einstein equation a viscosity, which is not affected by the mechanics of the viscometer, may be calculated if the size and diffusivity of the solute molecule are determined. The values of such viscosity calculated by using several diffusion equations compare favorably with the value calculated with the Stokes-Einstein equation. The dissolution rates of benzoic acid in aqueous solutions of three non-ionic suspending agents is related to the viscosity.