Surface charge engineering for structural control of colloidal silica rod-decorated silica particles and their flexible integration into magnetic core–multishell structures

In this study, the effect of surface modification and the resulting surface charge of colloidal silica seeds on the growth of silica rods during an emulsion droplet-based process is investigated. Through electrostatic interactions between negatively charged poly(vinylpyrrolidone) (PVP) and seed surfaces, significant PVP adsorption occurs as the seed surfaces are modified with positively charged cationic substances and then aged with PVP. This surface charge-enhanced PVP adsorption promotes the anchoring of water emulsion droplets, serving as the starting point for the growth of silica rods on the seed surfaces and leading to a high yield of silica rod-decorated particles during emulsion droplet-based growth. The surface properties, including surface charge and hydrophobicity, can be further modified by applying different cationic modifiers, which influence the morphology, structural architecture, and yield of the final product. We further demonstrated the versatility of this approach by successfully generating silica rod-decorated magnetic core (Fe₃O₄)–multishell (silica/polystyrene/titania) particles. The findings of this study highlight the critical role of surface charge engineering in controlling the structure and morphology of silica rod-decorated silica particles as well as their integration into complex multicomponent systems.