pH-responsive high internal phase emulsion stabilized by silicon-containing dynamic imine surfactant

Silicon-containing surfactants have attracted significant attentions both from fundamental researches and industrial applications, due to their outstanding surface/interfacial properties, but their preparations are usually cumbersome and low efficient. Here, a novel silicon-containing surfactant (2ASB-SiDA) was in situ prepared by mixing hydrophilic precursor (3-((2-(4-formylphenoxy)ethyl)dimethylammonio)propane-1-sulfonate, ASB) containing aldehyde group with commercial silicon-containing diamine (1,3-bis(3-aminopro pyl)tetramethyldisiloxane, SiDA) using dynamic covalent strategy. Characterizations of H-1 NMR and FTIR spectroscopies confirmed the formation of 2ASB-SiDA in situ with a conversion efficiency of aldehyde of > 80 % at pH 11-13, which is the first silicon-containing dynamic imine surfactant. Surface/interfacial tension revealed that 2ASB-SiDA has the ability to reduce surface tension similar to conventional hydrocarbon surfactants, but lower than covalent silicon-containing surfactants. However, 2ASB-SiDA showed lower Krafft temperature and better emulsification capacity than hydrocarbon dynamic imine surfactant with similar chain length and other common surfactant at the same concentration. Of interesting, highly stable high internal phase emulsion featuring gel-like characteristics can be obtained after homogenization only using 2ASB-SiDA (< 2 %, w/v, lower than the dosage required for common surfactants) prepared in situ as stabilizer, both polar (isopropyl myristate) and nonpolar oils (n-heptane, liquid paraffin, and D80), and remained stable even at high salt concentration (NaCl > 250 g/L, CaCl2 > 500 g/L). With alternatively changing pH between 11 and 8, high internal phase emulsion stabilized by 2ASB-SiDA can be reversibly switched on and off at least three cycles. The current work provides a new alternative for the preparation of silicon-containing surfactants and high internal phase emulsions.