Determination of the ideal surfactant concentration in miniemulsion polymerization

Abstract

In a miniemulsion polymerization, droplets are transformed to polymer particles keeping the particle size and composition during polymerization. To avoid changes due to coalescence or secondary nucleation, the surfactant concentration has to be adjusted according to the materials used and to the droplet size that is resulting from the emulsification process. To calculate the ideal surfactant concentration, it is important to know how many molecules are solved in the continuous phase. Therefore, a new method to calculate the ratio between adsorbed and dissolved surfactant molecules is presented and used to calculate the ideal surfactant concentration for polymerization of MMA miniemulsion droplets. The adsorption behavior of the surfactant is observed to influence the nucleation mechanism in miniemulsion polymerization significantly. This knowledge can be used to facilitate the design of the miniemulsion polymerization process. Differences in the adsorption behavior of the surfactants Lutensol AT50 and sodium dodecyl sulfate (SDS) influence the nucleation mechanism in miniemulsion polymerization. Whereas below the critical micelle concentration nearly all Lutensol AT50 molecules are adsorbed to the interface, the concentration of unadsorbed SDS molecules is significantly higher. That is why SDS promotes homogeneous nucleation. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.