Abstract
Pickering high internal phase emulsions (HIPEs) using micron-size polymeric particles as stabilizer were developed. By adding a small amount of surfactant to the Pickering HIPEs, macroporous polymers with a well-define open-cell structure were synthesized with these HIPEs as templates. Owing to the micron-size of the particles, the particle locations could be observed directly by laser scanning confocal microscopy. It was found that the excess and attached particles aggregated and formed thick particle layers around the droplets when the HIPE was stabilized solely by particles. These thick particle layers were extremely stable, and did not easily rupture during or after polymerization, which caused the resulting polymers to have a closed-cell structure. When a small amount of surfactant was added, it was found that the surfactant disaggregated the particles, leaving them well-dispersed in the continuous phase. Moreover, the surfactant tended to occupy the oil–water interface at the contact point of adjacent droplets, where the interconnecting pores were hence likely to be formed after consolidation of the continuous phase. This observation confirmed experimentally the mechanism of interconnecting pore formation in Pickering-HIPE-templated porous polymers proposed theoretically in previous works.
Highlights
We reported a series of open-cell porous polymers based on Pickering high internal phase emulsions (HIPEs) by adding a small amount ($1.0%) of surfactant to the emulsion before curing.[17,53,54,55]
Combined with SEM detection of the resulting polyPickering-HIPEs, it was found that a layer composed of closely packed particles surrounded the droplets in the HIPEs stabilized solely by particles, which hindered the formation of interconnected pores; and when a small amount of surfactant was added, it could be seen that disaggregated particles dispersed in the continuous phase and almost no particles were observed at the contact point of adjacent droplets
A Pickering HIPE stabilized by micron-size polymeric particles was prepared
Summary
Macroporous polymers have extensive applications in many elds, such as tissue engineering scaffolds,[1,2,3,4] controlled release,[5,6,7,8,9] ion adsorption,[10,11,12,13] separation[14,15] and supports for catalysis.[16,17,18,19,20] These applications normally require porous polymers with an open-cell structure. If the continuous phase of HIPE contains polymerizable monomers, polymerization could be initiated to produce macroporous polymers (polyHIPEs).[27,28] HIPEs are commonly stabilized by large amounts (5–50%)[27,29] of non-ionic surfactants, which are difficult to remove completely a er polymerization.[30] One way to solve this problem is to substitute nanoparticles for surfactants, and these particle-stabilized HIPEs are commonly called Pickering HIPEs. There have been many nanoparticles reported for the stabilisation of HIPE, such as modi ed titania particles,[31,32] silica particles,[33] MOFs,[34,35,36] and copolymer particles.[37,38,39,40,41,42,43] In addition, the use of particles as stabilizers endows the resulting porous materials with a number of bene ts. The particles used as stabilizers in Pickering HIPEs are irreversibly adsorbed at the water–oil interface because of their high energy of attachment, which
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