Droplet topology control of Janus emulsion prepared in one-step high energy mixing.

Droplet topology of a Janus emulsion in a vegetable oil (VO)/silicone oil (SO)/Tween 80 aqueous solution (Aq) system prepared in a one-step high energy mixing was investigated, mainly by image observation. Quantitative information of the topology was analyzed referring to the curvature of VO/SO interface, the location of contact plane, and the volume ratio of VO/SO within individual droplets. The results show that the "stable Janus emulsion" region in the phase map enlarges with surfactant concentration. The average volume ratio of two oil lobes within an individual Janus droplet agrees with the emulsion composition in the "stable Janus emulsion" region, which means that the droplet topology can be controlled by the emulsion preparation process within realistic limits. The volume ratio of VO/SO within individual droplet ranges from about 0.54 to 0.17 in the VO/SO/3 wt% Tween 80(Aq) system, beyond which separate VO and SO droplets are observed. The topology of a Janus droplet is found to be determined by both the contact angle of three liquids in the contact line and the location of the contact plane. The contact angle of the oil cap is determined by the interfacial tension referring to the local equilibrium. The location of the contact plane is the dominant factor determining the volume ratio of two oil lobes. Composition change in the emulsion results in the corresponding tune of the location of contact plane and subsequently, the volume ratio of two oils within Janus droplets.