One-step preparation of photoresponsive microcapsules based on the interfacial self-assembly of an azopyridine coordination polymer

Abstract

In recent decades, stimuli-responsive microcapsules have attracted increasing attention due to their potential applications as microreactors for drug delivery, catalytic reactions, etc.; however, the complicated preparation process and the difficulty of size fixation and recycling need to be addressed. In this work, we developed a one-step preparation method to fabricate photoresponsive microcapsules based on the interfacial self-assembly of an azopyridine coordination polymer. The coordination of silver ions and ligands was performed in situ at an oil–water interface, and the coordination polymer self-assembled into nanofibers, which stabilized the Pickering emulsion and produced water-in-oil microcapsules. Additionally, microcapsules with a uniform size were prepared based on a microfluidic process. Both the crystal structure and the Janus surface of nanofibers were determined to elucidate the mechanism of self-assembly and interface stabilization. When the microcapsules were irradiated with 365 nm UV light, the cis isomerization of the azo group in the coordination polymer led to the disassembly and dissolution of the nanofibers, resulting in fusion of the microcapsules and demulsification of the Pickering emulsion. Conversely, visible light and heating triggered the trans isomerization of the azopyridine coordination polymer and thus caused regeneration of the nanofibers and recovery of the microcapsules. Finally, microcapsules encapsulating several reactants were employed in the pH-indicator discoloration reaction and the enzyme-catalyzed decomposition of H2O2 to demonstrate their feasibility as photocontrolled microreactors. This kind of photoresponsive microcapsule with one-step preparation and good recyclability might have potential applications in the field of microreactors.