Influence of Surfactant on Crystallization Kinetics of Stearic Acid

Crystallization of organic crystals from solutions is used in many industries. Depending on the application, control over size and shape of crystals is often desired and is achieved by tailoring process parameters such as rate of cooling and/or shear rate, or via the use of certain additives. In this study, the effect of Span 80 on crystallization of stearic acid from its supersaturated solution in mineral oil is presented. The rate of growth of the C-form crystals has been determined to increase almost quadratically with relative supersaturation. In the presence of Span 80, growth was much slower, which led to a gradual change in shape and aspect ratio of the crystals. A model based on competitive adsorption between surfactant and solute at the growing interface has been used to explain the role of surfactant. In addition, the rate of nucleation decreased in the presence of Span 80, indicative of a higher interfacial energy penalty during nucleation.