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

Abstract

The 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.

Poly(methylvinylsiloxane)-Based High Internal Phase Emulsion-Templated Materials (polyHIPEs)—Preparation, Incorporation of Palladium, and Catalytic Properties

“…The microstructure of the synthesized materials clearly depended on the amount of D 4 H added to HIPE, that is, on the V 3 polymer cross-linking degree. SEM images (Figure 1) show that only in the V3_1:1 and V3_1:1.5 samples, of higher polymer cross-linking levels, pore morphology typical of polyHIPEs [7][8][9][10][11][12][13][14][15]19 developed. In contrast, the V3_1:0.44 and V3_1:0.66 samples, of lower polymer cross-linking degrees, contained "flat", nonporous areas on their surfaces, more numerous in the case of the former than the latter one (Figure 1).…”

“…Since their first description, polyHIPEs synthesized via conventional radical copolymerization of styrene and divinylbenzene in w/o emulsions have been the focus of numerous studies. − However, other monomers, polymerization methods, and/or types of emulsion have been used in HIPE templating as well. For example, ring-opening copolymerization of ε-caprolactone and a difunctional monomer (4,4-bioxepanyl-7,7′-dione) in oil-oil (o/o) HIPE has led to macroporous polyesters showing the shape memory effect .…”

Facile Fabrication of Superhydrophobic Graphene/Polystyrene Foams for Efficient and Continuous Separation of Immiscible and Emulsified Oil/Water Mixtures

“…The organic phase, St and DVB, was then polymerized to form the skeleton of the porous material [ 48 ], and the water phase was removed from the pore cavities to give the GN/PSt porous materials with high porosities and open pore structures ( Figure 2 ). As seen in the SEM images in Figure 2 a, the GN/PSt composites contained interconnected polymer walls that formed large spherical pores ( Figure 2 a), and many smaller pores were present within the polymer skeleton ( Figure 2 b) [ 49 ]. GN randomly penetrated into the matrix of the porous materials, resulting in a rougher microstructure and lower surface energy ( Figure 2 c–f) [ 50 ].…”

Dendritic Macrosurfactant Assembly for Physical Functionalization of HIPE-Templated Polymers

“…Other studies suggested the role of phase separation and vacuum induction [48]. Li et al [49] suggested that pore formation is not related to vacuum and attributed it to the combination of volume contraction and surfactant migration upon gelation. Closed cellular polyHIPE is typically obtained when nanoparticles are used as the stabilizer of a HIPE system (called Pickering emulsion).…”