An investigation into the nature and potential of in-situ surfactants for low energy miniemulsification

Abstract

HypothesisIt has been reported that surfactants generated in-situ are more efficient than their preformed analogues in preparation of miniemulsions for application in miniemulsion polymerization but conflicting experimental evidence exists over their use. Herein, the potential of preparing miniemulsions using in-situ generated surfactants is evaluated using KOH/oleic acid as a model system. ExperimentsThe kinetics of miniemulsification using either preformed or in-situ generated potassium oleate were evaluated by monitoring the evolution of droplet size, pH and conductivity during miniemulsification using sonication. Subsequently, the kinetics of surfactant adsorption to the monomer/water interface were studied using dynamic interfacial tension measurements. Finally, the ability of in-situ generated potassium oleate to produce miniemulsions under low shear was evaluated under a range of conditions. FindingsNo difference in the evolution of droplet size, pH or conductivity was observed between the two surfactant systems when sonication was applied. Dynamic interfacial tension measurements showed that using in-situ generated potassium oleate, interfacial tension is significantly lower initially, but at long times the two surfactant systems reach similar values. Low shear emulsification by in-situ generated potassium oleate resulted in a bimodal droplet distribution. Only at very low oil contents with high surfactant concentration is the number of nanometer sized droplets large enough to account for a miniemulsion polymerization mechanism.