Effect of surfactants on the degree of polydispersity of suspensions of polystyrene latex spheres

The paper considers methods for obtaining suspensions based on monodispersed particles in the form of polystyrene latex spheres. Such suspensions can be used as particle size measures, necessary to ensure the uniformity of measuring particle size distribution in aerosols, suspensions, and powdered materials. It was shown that under different conditions of synthesizing monodisperse suspensions of polystyrene latex spheres, both monodisperse and polydisperse samples can be obtained. The effect of the composition and degree of surfactant solubility in a styrene-water emulsion on the size of polystyrene latex sphere suspension particles, obtained as a result of emulsion polymerization, and degree of their polydispersity has been studied. The metrological characteristics of polystyrene latex sphere suspensions obtained in this study based on various salts of lauric acids (e.g., sodium, potassium, and lithium laurates) were analyzed using dynamic light scattering and laser light diffraction techniques. It was found that the size and degree of polydispersity of suspension particles is primarily affected by surfactant solubility and surface tension of the interfacial styrene-water layer at the time of particle formation. The effect of the reaction rate, as well as the surfactant concentration, on the size and polydispersity of the synthesized particles has been studied. It was found that by using potassium persulfate as a reaction initiator, sodium or potassium laurate-based suspensions exhibit monodisperse particle size distribution. The degree of polydispersity of lithium laurate-based suspensions appears to be 1.5 to 2 times higher compared to other analyzed suspensions. The use of azoisobutyronitrile as an initiator made it possible to achieve monodispersity of all suspension samples. It has been experimentally established that monodispersity of the samples is determined by the time it takes to form polymer-monomer particles, which is comparable to the monomer transformation rate. The obtained results will be used to develop the particle size measures for storage and reproduction of particle size values in a liquid medium.