Microfluidic Synthesis of Photoresponsive Spool-Like Block Copolymer Nanoparticles: Flow-Directed Formation and Light-Triggered Dissociation.

We demonstrate flow-directed production of nanoparticles of the photoresponsive block copolymer poly(o-nitrobenzyl acrylate)-b-polydimethylacrylamide in a gas-liquid microfluidic reactor. Microfluidic formation produced a variety of morphologies dependent on flow rate, with spheres and short cylinders, then large compound micelles, then unique spooled cylinders appearing as flow rate increased. The higher excess free energy of spooled cylinders relative to the quiescent equilibrium state is evidenced by their faster off-chip relaxation times (~1 day) as compared to other flow-directed structures. Comparison of light-triggered dissociation of flow-directed nanoparticles prepared at two different flow rates shows faster disruption of nanoparticles prepared at the higher flow rate. The application of variable flow to direct both structure and responsivity suggests interesting possibilities for controlled microfluidic manufacturing of "smart" polymeric colloids. [ABSTRACT FROM AUTHOR]