Interconnected Pickering Polymerized High Internal Phase Emulsions

High internal phase emulsions are used as a template to produce highly porous and interconnected polymeric materials. The method simply relies on the solidification of the continuous phase and the removal of the internal phase. Consequently, materials with a porosity correlated with the amount of the internal phase are obtained. If the solidification of the continuous phase involves the polymerization, the resultant material is called Polymerized High Internal Phase Emulsions (PolyHIPE). Since the method relies on the preparation of emulsion, it necessitates the utilization emulsion stabilizer. Surfactants are commonly used stabilizers to obtain interconnected and porous PolyHIPEs. Alternative stabilizers are solid particles, the emulsion stabilized with the colloidal particles are called Pickering emulsions. Although Pickering emulsions offer various advantages over surfactants, the obtained PolyHIPE from Pickering HIPEs do not exhibit interconnected porous structures since they do not exhibit pore throats unlike PolyHIPEs obtained from surfactant stabilized HIPE. On the other hand, the formation of pore throats is still under debate. While Pickering PolyHIPEs are known for their closed cellular structure, there are a few reports demonstrating the interconnected Pickering PolyHIPEs, without mentioning the details of how they are formed. In this study, we investigated the pore throat formation in Pickering PolyHIPEs and proposed a new mechanism in pore throat formation in Pickering PolyHIPEs for the first time. The effect of various parameters on the formation of pore throats is evaluated; particle size, particle concentration, internal phase volume, and particle type. The investigation led us to conclude that the arrested coalescence phenomenon, observed in Pickering emulsion droplets, can be the mechanism. Further, the effect of particle hydrophilicity was evaluated on Pickering PolyHIPE morphology, as well as on HIPE rheology and emulsion interfacial rheology. It is concluded that as the particle hydrophilicity increases, previously observed atypical; large, and interconnected porous Pickering PolyHIPE morphology turns into a typical closed porous Pickering PolyHIPE. Additionally, the closed pores are found to be well-decorated with hydrophilic particles. Furthermore, it is hypothesized that the utilization of both hydrophobic and hydrophilic particles as HIPE stabilizers can lead to the formation of interconnected and hydrophilic particle-decorated porous Pickering PolyHIPE. ZIF-8 is chosen as a functional and hydrophilic co-stabilizer. The efficacy of ZIF-8 decoration on the pores of PolyHIPEs is investigated and it was found that the hydrophobic-hydrophilic particle co-stabilization efficiently produces interconnected and ZIF-8 decorated Pickering PolyHIPEs.