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.