Single-Hole Janus Hollow Sphere.

Cross-linked epoxy resin (EP) single-hole Janus hollow spheres are prepared by cross-linking induced phase separation within an emulsion droplet and selective modification. The droplet is composed of an EP oligomer, toluene, and hexadecane. 2-Ethyl-4-methylimidazole is used as the cross-linker added to the aqueous phase. During the cross-linking, hexadecane forms an eccentric core in the cross-linked EP sphere. A single hole forms across the shell after dissolving the solvents, and a single-hole hollow sphere is achieved. The hole and cavity size are controlled by adjusting the solvent content and cross-linker concentration. Furthermore, frozen wax is used as the core material instead of hexadecane to effectively protect the sphere's interior surface. Selective modification of the exterior and interior surfaces is thus permitted. As an example, a responsive single-hole Janus hollow sphere is prepared by the favorable growth of a silica-polyoxyethylene composite layer onto the exterior surface and a selective grafting of poly(2-diethylaminoethyl methacrylate) (PDEAEMA) by atom-transfer radical polymerization (ATRP) onto the interior. The Janus sphere is water-dispersible and controllably captures and releases oil from the aqueous environment as triggered by the pH value.