Influence of experimental parameters on the formation and stability of silica-wax colloidosomes

Silica-wax colloidosomes find application in various fields, for instance through their use as microencapsules for triggered release of chemical components or as precursors for the production of Janus particles. The characteristics of these colloidosomes are highly dependent on the particles/water-oil system composition and experimental parameters.

Different colloidosomes were prepared using silica particles (D¯ ≈ 295 nm) and a positively charged surfactant (cetyltrimethylammonium bromide, CTAB) as co-stabilizers of a wax in water. The CTAB concentration, type of stirring and wax addition procedure were systematically varied. The silica particles and colloidosomes formed were analysed by Scanning Electron Microscopy (SEM) and Dynamic Light Scattering (DLS). The final percentage of the silica particles embedded on the wax colloidosomes (embedding yield) was estimated by a gravimetric method and the formation of monolayer or multilayer/clusters of silica particles at the wax surface was inspected with SEM.

The CTAB concentration and the wax addition procedure play a major role in obtaining an embedding yield close to 100% and a monolayer coverage of the colloidosomes surface. The results indicate the existence of a mechanism consisting of a dynamic redistribution of the surfactant between the interfaces present in the emulsion. The practical and theoretical insights provided can be used towards an efficient production and scale-up of silica-wax colloidosomes.