A rapidly switchable CO2-responsive Pickering emulsions based on supramolecular amphiphilic surfactants and nano-SiO2

Abstract

A novel rapidly switchable CO2/N2-responsive Pickering emulsifier based on supramolecular amphiphilic surfactants (SDOA) and nano-SiO2 has been fabricated. SDOA was constructed by mixing Jeffamine D-230 and oleic acid (HOA) at 1:1 stoichiometric ratio. Compared with conventional small-molecule emulsifiers, the novel rapidly switchable CO2/N2-responsive Pickering emulsifier was prepared with inexpensive raw materials by a simple method, and there was no contaminant generation during synthesis. A new CO2/N2-responsive Pickering emulsion was prepared on this basis, and its stable performance and responsiveness were investigated in depth. The results show that this emulsion can be stable for a long time (more than 30 days) at a low surfactant dosage (0.5 mmol/L) through in situ hydrophobization of SiO2 nanoparticles by hydrogen bonding and electrostatic adsorption. In addition, the emulsion broke rapidly and completely after 10 s of CO2 introduction into the stable emulsion, and the emulsion could be reconstructed in response to N2 purging for 5 min at 60 ℃ followed by homogenization. The switching behavior of the emulsion is due to decomposition of the pseudo amphiphile by bubbling CO2 into the system and both the protonated D-230 ions and the neutral HOA produced have no in situ hydrophobization to SiO2 particles. At 60 ℃, the influx of N2 will drive out CO2, making HOA re-transform into hydroxide ion, and after re-combining with D-230 ion, it can again perform in-situ hydrophobization on SiO2 particles, thus forming a stable emulsion. Thanks to the ability of SiO2 nanoparticles and D-230 ions to maintain electrostatic adsorption after the passage of CO2, compared with previous studies, the emulsion can be completely demulsified at a higher pH value (about 5.5), fewer bicarcarbonate roots are formed, less CO2 needs to be introduced, and N2 required to re-stabilize the emulsion is also reduced. This greatly increases the response efficiency of the emulsion and reduces the energy loss and the cost of putting the emulsion system into practical application. This research has important implications for fossil fuel generation, production and transportation of crude oil, and other areas.