Tailoring Surface Morphology of Silica Colloids for Tunable Pickering Emulsions

Colloids with surface roughness are of increasing interest because of their unique structural features and broad utility in adsorption, catalysis, drug delivery, and emulsion stabilization. In this work, we have investigated the etching of silica particles using hydrochloric acid (HCl) and sodium hydroxide (NaOH) to explore the effects of acids and bases on surface morphology and physicochemical properties as a function of concentration and exposure time. Silica particles were exposed to etchants of different concentrations and exposure times to observe the gradual change in surface roughness and porosity. The results revealed that both HCl and NaOH effectively modulate the surface area, pore volume, and average pore size, with NaOH acting as a more efficient etching agent, enabling controlled formation of mesoporous structures with pore diameters up to 22 nm, significantly exceeding those typically reported for self-templated systems. The effectiveness of these structural changes was further demonstrated by their application in stabilizing Pickering emulsions for both water-in-oil (W/O) and oil-in-water (O/W). Because of enhanced roughness, rough particles show higher emulsion stability than smooth ones in both cases, highlighting the importance of controlled etching in designing colloids for emulsion-based applications.