Surface-engineered polyurea microcapsules via amphiphilic copolymer emulsifiers

The development of surface-functionalized polymeric microcapsules is a rapidly growing field with emerging applications in advanced materials and controlled release technologies. This work focuses on the design and synthesis of polyurea microcapsules with a negatively charged surface by using amphiphilic copolymers based on sodium 4-styrenesulfonate (SSNa) as emulsifiers in oil-in-water emulsion polymerization. Unlike traditional systems that mostly rely on poly(vinyl alcohol) (PVA), the proposed copolymers are integrally incorporated into the microcapsules' shell, providing a high negative surface charge (about -38 mV) and reactive groups ( e.g. anionic sulfonate groups). The influence of the molecular structure and hydrophilic/lipophilic balance of the copolymers on emulsion stability was systematically examined, with sodium poly(4-styrene sulfonate-co-glycidyl methacrylate), P(SSNa-co-GMA40), demonstrating the best performance. The microcapsules produced were subsequently characterized by morphological examination and surface charge analysis. Their potential for further modification via ion exchange with cationic organic species was explored. Moreover, the presence of a negative charge was crucial for the adsorption of cationic dyes, such as Rhodamine B, as reflected by the high removal efficiency (practically 100% at low dye concentration) achieved by microcapsules, leading to highly luminescent colored shell-decorated microcapsules. The results emphasize the significance of molecular design of emulsifiers in developing functional microcapsules with enhanced properties.