Stabilization of 4FS(EO)2 constructed water-in-carbon dioxide microemulsions (W/C μEs) with nonfluorinated co-surfactants
Three nonfluorinated co-surfactants, sodium bis (2-(isopropoxy)-ethanol) sulfonate (di-IOESS), sodium bis (3,5,5-trimethyl-hexanol) sulfonate (di-TMHSS) and sodium bis (2-(pivaloyloxy)-ethanol) sulfonate (di-POESS) were synthesized to replace partial sodium bis (3,3,4,4,5,5,6,6,6-nonafluoro-hexanol) sulfonate (4FS(EO) 2 ) to stabilize W/C microemulsions to decrease the fluorine content. The results showed that the stabilization ability of the co-surfactants at less than 55 °C was in the following order: di-TMHSS > di-POESS > di-IOESS. Results for MD simulations proved that the co-surfactants mainly changed the packing efficiency of the surfactant short chains. The flexible co-surfactant tails could maintain the bending fraction of the surfactant short tail at a low level and the appropriate length of co-surfactant tails helped to occupy more volume at the interface. Therefore, the nonfluorinated co-surfactants with flexible branched tails in an appropriate length relatively to the surfactant tails were conducive to replace partial fluorinated surfactants, which may help for designing nonfluorinated co-surfactants to decrease the fluorine content in W/C microemulsions.
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