Microfluidic fabrication of porous polymer microspheres: dual reactions in single droplets

We report the microfluidic fabrication of macroporous polymer microspheres via the simultaneous reactions within single droplets, induced by UV irradiation. The aqueous phase of the reaction is the decomposition of H(2)O(2) to yield oxygen, whereas the organic phase is the polymerization of NOA 61, ethylene glycol dimethacrylate (EGDMA), and tri(propylene glycol) diacrylate (TPGDA) precursors. We first used a liquid polymer precursor to encapsulate a multiple number of magnetic Fe(3)O(4) colloidal suspension (MCS) droplets in a core-shell structure, for the purpose of studying the number of such encapsulated droplets that can be reliably controlled through the variation of flow rates. It was found that the formation of one shell with one, two, three, or more encapsulated droplets is possible. Subsequently, the H(2)O(2) solution was encapsulated in the same way, after which we investigated its decomposition under UV irradiation, which simultaneously induces the polymerization of the encapsulating shell. Because the H(2)O(2) decomposition leads to the release of oxygen, porous microspheres were obtained from a combined H(2)O(2) decomposition/polymer precursor polymerization reaction. The multiplicity of the initially encapsulated H(2)O(2) droplets ensures the homogeneous distribution of the pores. The pores inside the micrometer-sized spheres range from several micrometers to tens of micrometers, and the maximum internal void volume fraction can attain 70%, similar to that of high polymerized high internal phase emulsion (polyHIPE).