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

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