Generating stable pickering emulsions using metal oxide particles

Abstract

Particle wettability is an important factor which determines the stability of a Pickering emulsion. Hydrophobic silanes are often grafted onto particles to obtain intermediate wettability. However, amphiphobic silanes have contrasting properties and have yet to be used as a coating. In this study, hydrophobic and amphiphobic particles were used to observe their effect on emulsion stability. Contact angles and surface energies of each silane was measured to determine their properties. TiO2 particles were coated with different silanes and homogenised with wax and water. Homogenised samples were observed under the Scanning Electron Microscope (SEM) to determine droplet morphology and size. A lower FAS concentration and 1.80wt% of particles gave rise to a stable emulsion. The droplets had a relatively small size distribution and were covered with a monolayer of particles. The FAS emulsions were more stable as lesser droplet coalescence was observed. In TEOS emulsions, an increase in particle content gave rise to smaller droplets. However, droplet size plateaued beyond 3.57wt% because there was insufficient energy to further decrease droplet size. Coagulated droplets were more dominant in the TEOS emulsions. The trends presented by FAS emulsions varied from that of hydrophobic silanes such as TEOS. Each silane achieved optimal conditions with different parameters due to differing emulsion formation mechanisms. Future investigation on experiments with a 1:4 FAS concentration is needed. Higher homogenizing speed or longer emulsification durations can be used. Increasing input energy would create a larger interfacial area and provide higher chances for FAS particles to adsorb at the interfaces.