Preparation of High Internal Water-Phase Double Emulsions Stabilized by a Single Anionic Surfactant for Fabricating Interconnecting Porous Polymer Microspheres

Herein we report a one-step method to prepare high internal water-phase double emulsions (W/O/W) via catastrophic phase inversion of water-in-oil high internal phase emulsions (W/O HIPEs) stabilized solely by 12-acryloxy-9-octadecenoic acid (AOA) through increasing the content of water phase. This is the first time for double emulsions to be stabilized solely by a single small molecular surfactant, which are usually costabilized by both hydrophilic and hydrophobic surfactants. After neutralized with ammonia, AOA is confirmed to be capable of stabilizing both W/O emulsions and O/W emulsions, which may account for its unique ability to stabilize double emulsions. The effects of different conditions (including changing the concentrations of AOA and salt (NaCl), pH value, the polarity of oils, the addition interval of water and stirring rate, etc.) on the formation and the stability of double emulsions as well as the inversion point have been investigated by using optical microscopy and conductivity monitoring. Finally, porous polymer microspheres with high interconnection (polyHIPE microspheres) were fabricated by gamma-ray initiated polymerization of the as-prepared double emulsions composed of different monomers (styrene, or n-butyl acrylate, or methyl methacrylate), which have been confirmed by scanning electron microscopy. Our method is facile and effective for preparing high interconnecting porous polymer microspheres without tedious post-treatment of the products in common emulsion polymerization due to the use of polymerizable surfactant.