The development of negatively charged polystyrene nanoparticles (NPs) and their assembly at oil-water interface assembly is reported. The motivation stems from their potential applications across various fields, including drug delivery, biomedical imaging, environmental remediation, electronics, and more. The study focuses into the colloidal stability of the synthesized nanoparticles, exploring electrostatic and steric stabilization effects. The synthesis process involves miniemulsion polymerization to form polystyrene core, grafting of poly glycidyl methacrylate (PGMA) brushes using divinylbenzene (DVB) as a crosslinker, and sulfonation of the epoxy ring in the PGMA brushes for improved stability in the presence of various electrolyte solutions. The NPs were characterized by a comprehensive array of techniques including dynamic light scattering (DLS), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Also, part of the study are efforts to characterize the NP assembly at oil-water interfaces under different conditions such as different pH or in the presence of various salts. The study concludes with recommendations for future directions including ideas for improvements of colloidal stabilization and investigating surfactant release mechanisms for controlled release in desired environments. The study adds new insights to our understanding of the behavior of NPs bearing polyelectrolyte brushes on their surface and their assembly at oil-water interfaces.