A series of Janus hemispheres with a patchy hemispherical surface and a flat undersurface were synthesized through controlled polymerization-induced phase separation within emulsified wax droplets. The hemispherical shape was generated through the polymerization of styrene within wax droplets, followed by the grafting of hydrophilic polymers on the exposed surface. Then, the patchy hemispherical surface was achieved after introducing the hydrophobic acrylate monomers within wax droplets and controlling the polymerization-induced phase separation. The morphological evolution of patches was recorded via the reaction time, followed by their morphological regulation through the type, feeding amount, and cross-linking degree of acrylate monomers. A functional monomer, vinyl benzyl chloride (VBC), was also used to copolymerize the patches for grafting a zwitterionic polymer via surface-initiated atom transfer radical polymerization (SI-ATRP). The as-obtained Janus hemispheres were employed to fabricate robust coatings with wettability tuned from superhydrophobicity to underwater superoleophobicity by the grafted zwitterionic polymers.