Abstract
The dissolution rate of benzoic acid in aqueous sucrose and methylcellulose solutions is inversely proportional to the viscosity of the dissolution medium. The total solubility of benzoic acid in aqueous solutions of polysorbate 80 increases linearly as the concentration of the surfactant is increased. As the concentration of polysorbate 80 is increased with a limited increase in viscosity of the micellar solution, the dissolution rate of benzoic acid is increased to a maximum rate and is related to the total solubility as depicted by the Noyes‐Whitney relation. At concentrations of polysorbate 80 exceeding the concentration corresponding to the maximum dissolution rate, the dissolution rate is decreased as the concentration of the surfactant is increased. Because the dissolution rate is inversely proportional to the viscosity, high concentrations of polysorbate 80 increase the viscosity of the micellar solutions to the extent that the dissolution rate is slowed although the total solubility is greatly increased. In micellar solutions maintained at a constant viscosity, the total solubility of benzoic acid increases linearly as the concentration of the surfactant is increased. The dissolution rate of benzoic acid in micellar solutions with a constant viscosity increases progressively without a maximum rate as the concentration of the surfactant is increased.
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