Templated Synthesis of Polymer-Based Yolk/Shell Particles\nwith Tunable Morphologies

Abstract

Polymer-based\nyolk/shell particles with functional components,\nincluding porous shells, removable shells, hollow cavities, or functional\ncores, are of potential utility in many contexts. We report strategies\nfor the synthesis of polymer-based yolk/shell particles templated\nby droplets of polymerizable oils contained within hollow and semi-permeable\npolymer capsules. Partial filling of degradable microcapsules with\nmixtures of vinyl monomers, followed by extraction into water, yielded\nyolk/shell-type structures composed of monomer droplets surrounded\nby larger polymeric shells. These encapsulated droplets can undergo\nchanges in size (from micro- to nanoscale), shape (from spherical\nto lemon-like), and mobility upon exposure to different conditions\nand stimuli. Photopolymerization of monomer droplets yielded cross-linked\nparticle cores with morphologies templated by those of the liquid\ndroplets, enabling the synthesis of various types of polymer yolk/shell\nstructures. SEM images of polymer particle yolks after removal of\nsurrounding capsules revealed spherical or lemon-like shapes with\nsmooth morphologies. The aqueous environments within these yolk/shell\nstructures can be used to host chemical reactions to further define\nand tailor particle properties. Thermal polymerization and subsequent\ncross-linking of poly­(acrylic acid) yielded gels inside the capsules\nand a new “hard-boiled” yolk/shell morphology, with\npolymer cores imbedded in a solid, gel-like phase contained within\na surrounding semi-permeable capsule.