Emulsions are used in a wide range of fields, including foods, cosmetics, pharmaceuticals, paints, and adhesives. Emulsions are also applied to polymer particle synthesis. It is important to improve the stability of emulsions, which are usually unstable in thermodynamics, and to design droplet diameter size. A large amount of surfactant needs to be added to improve the stability of the emulsion. Ultrasound is also known to be useful in the preparation of emulsions with fine droplet diameters. In addition, a tandem emulsification method has been proposed, in which ultrasound waves of low to high frequencies are sequentially irradiated. It has been reported that this method is capable of preparing very stable nanoemulsions with droplet diameters of several tens of nm.
In this study, the tandem emulsification method is used to prepare O/W emulsions with the styrene monomer as the dispersed phase before polymerization, and then the emulsions are heated to proceed the polymerization reaction for polystyrene particle synthesis. The effects of operating conditions on polymer particle size and yield were investigated. Kinetic analysis was also performed based on results of yields. Polystyrene particles of 5 - 10 μm were synthesized in around a yield of 80 %. There were conditions under which ultrasonic irradiation of the crude emulsions prepared by stirring decreased the size of the droplets. However, from the kinetic analysis, the rate constants were almost the same independent of the operational conditions. It is suggested that the relationship between the droplet diameter of the crude emulsion and the ultrasonic frequency irradiated in the second stage influences droplet refinement.
