Selective emulsion inversion in an equilibrium Janus drop. 1. Unlimited space

[Display omitted] •The topology of a Janus drop in an infinite aqueous continuous phase was calculated.•Interfacial tension equilibrium was retained at the three liquid contact line.•The radius of O1 was constant, while that of O2 was varied.•Infinite volume of O2 gave limited coverage of O1.•Subsequent water removal gave inversion emulsion from (O1+O2)/W to (O1+W)/O2. The potential for a catastrophic inversion of one phase in a Janus emulsion drop was investigated by local equilibrium calculations of a single Janus drop of two mutually insoluble oils, O1 and O2, in an infinite aqueous continuous phase, (O1+O2)/W. The relative volume of the oil with less interfacial tension towards water, O2, was increased, while the radius of the O1 part of the drop was held constant at unity. The limiting fraction of O1 covered by O2 was calculated for infinite O2 volume for a selected interfacial tension combination. After the O2 volume reached infinity, the volume of the continuous aqueous phase was reduced to finite values, leading to a selective inversion of the emulsion from (O1+O2)/W to (W+O1)/O2. Thenceforward, further removal of the water led to an additional reduction of the size and radius of the water cap.