Preparation of particle-stabilized oil-in-water emulsions with the microchannel emulsification method

Oil-in-water (o/w) emulsions stabilized by aggregates of completely hydrophilic silica nanoparticles alone were prepared by the microchannel emulsification method. The emulsification conditions and mechanism in a cross-flow type microchannel setup were investigated. Increasing the flow rate of the continuous phase along the exits of microchannels prevented the coalescence of droplets. The emulsions obtained are stable over several months with a much reduced polydispersity than those prepared with a homogenizer. The silica aggregates form shell-like layers around the droplets with a thickness in agreement with the size of the aggregates in bulk, indicating that silica aggregates form a monolayer on droplet surfaces. On the other hand, the adsorbed layer of silica aggregates prepared with a homogenizer was thinner than that prepared with microchannel emulsification, indicating the breakup of the aggregates during homogenization. Results reveal that microchannel emulsification offers advantages over the conventional mechanical emulsification in the preparation of fine particle-stabilized emulsions since it involves no extensive mechanical shearing.