Evolution of a Radical‐Triggered Polymerizing High Internal Phase Emulsion into an Open‐Cellular Monolith

Abstract

AbstractThe time and manner by which initially discrete cells in a high internal phase emulsion (HIPE) become highly interconnected by windows during/after polymerization (polyHIPE) remain a controversy. Water‐in‐oil HIPE with styrene/divinylbenzene as the oil phase is one of the most widely studied systems. Here, new evidence is presented on the evolution of polyHIPE with the aid of a macrosurfactant and new instruments. The macrosurfactant has a branched polyethylenimine as the hydrophilic head and polystyrene chains as the hydrophobic tail. It can stabilize HIPE within a wide range of dosages and lead to different polyHIPE morphologies, all of which are proven to be of open‐cellular monolith. At a low macrosurfactant dosage, the windows that interconnect the cells are sparse but large and can be effectively detected with a 3D optical microscope (3DOM) and a 2D photothermal infrared (2D PTIR) spectrometer in an open environment. 3DOM detection supports the claim that windows form during HIPE polymerization. Tests involving the extraction of pre‐colored water droplets of the polymerizing HIPE also lend support to the formation of an open‐cellular structure during polymerization. 2D PTIR provides evidence on phase separation on the surface once covered by the macrosurfactant, which favors window development.