PolyHIPEs are porous emulsion-templated polymers that are usually synthesized within surfactant-stabilized water-in-oil high internal phase emulsions (HIPEs). Typical polyHIPEs have highly interconnected porous microstructures, low bulk densities, and the ability to rapidly absorb large quantities of liquid through capillary action. Surfactant-free polyHIPEs can be synthesized through the formation of nanoparticle-stabilized Pickering HIPEs. In this work, the functionalized silica nanoparticles at the oil-water interface not only stabilized the HIPEs, but could also act as crosslinking centers and/or as polymerization initiators. Changing the type of stabilization, the crosslinking strategy, the locus of initiation, or the polymerization mechanism produced profound differences in the porous microstructure and in the properties.
Porous, temperature-responsive shape memory polymers (SMPs) based on acrylates and methacrylates with crystallizable side-chains were templated within Pickering HIPEs. These porous SMPs exhibited fixity ratios of 1.0 for compressive strains of 0.70 and relatively high recovery ratios. While the methacrylate-based SMP exhibited a single-stage recovery, the acrylate-based SMP, whose side-chains were identical, exhibited a two-stage recovery that was associated with the individual thermal transitions of two different crystalline phases. The recovery behaviour was described using Kelvin-Voigt units in series with the dependence of viscosity on temperature described using a WLF-like relationship. Liquid droplet elastomers (LDEs) are novel, tissue-like, emulsion-templated elastomeric monoliths that contain around 85 % water in the form of individually encapsulated micrometer-scale droplets. The polyhedral shape of the droplets results from the need to accommodate a high volume fraction of water and is "locked-in" during polymerization. The water retention in these unique materials was exceedingly high, enhancing the resistance to compressive deformation and to ignition upon direct exposure to a flame.
