Formation of O/W macroemulsions with a circular microfluidic device using saponin and potato starch

The formation of O/W macroemulsions stabilized by a non-ionic surfactant (Quillaja saponin) and gelatinized starch was investigated using a flow focusing device consisting of circular microchannels. Droplets of hot oil (Toil = 338 K) were dispersed into an aqueous solution of saponin and potato starch granules. The oil fraction varied between 0.9% and 5% (dilute macroemulsions) while the starch-to-saponin concentration ratio, α, ranged between 0 and 187.5. The heat transfer from the hot oil droplet (340 to 725 μm in diameter) induced the gelatinization of the adjacent starch granules to create a thin-shell around the oil droplet. In order to optimize the droplet generation, the physical properties of fluids were determined and the interactions between saponin and gelatinized starch granules were studied by measuring the specific conductivity. In particular, the onset, peak and end temperatures of starch gelatinization were determined. For various α, the monodispersed regime was determined by measuring the oil droplet volume Vdrop. For all cases studied, Vdrop followed a power dependence with the flow rate of the aqueous phase but the exponents were different (0.65 < n < 0.9). The formation process, i.e. the dripping and jetting regime, and the generation time of oil droplets were also detailed.