Light-Triggered Reversible Self-Engulfing of Janus Nanoparticles.

Block copolymers containing azobenzene liquid crystalline (LC) mesogen are used to prepare snowman-like Janus nanoparticles (NPs) by emulsion solvent evaporation. The azobenzene-containing poly(methacrylate) (PMAAz) head of the Janus NPs is in the smectic LC phase with ordered stripes, which becomes amorphous and enlarged due to trans/cis transformation under UV irradiation. The expanded PMAAz can consequently engulf the other head. The self-engulfed NPs can recover to their original state in both shape and LC state via visible-light irradiation. This strategy is promising for programmable load and release of different payloads by remote trigger using light.