Silica Nanoparticles vs Nanocapsules from Dye-Stabilized Emulsions: Role of the Comonomer

Dye-stabilized o/w miniemulsions offer an effective platform for synthesizing silica nano-objects via a sol-gel process at the oil-water interface. The choice of the organotrialkoxysilane precursor has a significant impact on the morphology of the resulting silica structures. When Congo red is used as a stabilizer, narrowly distributed nanoparticles below 30 nm and nanocapsules with diameters under 500 nm are formed. The subtle influence of the selected monomer is linked to the kinetics of the sol-gel process, which depend on factors such as molecular structure, comonomer content, and temperature. Factors that accelerate the sol-gel reaction, such as lower steric demand, higher water solubility of the precursor, and temperature increase, favor capsule formation, while slower reactions tend to produce particles instead.