Economical and Efficient Hybrid Surfactant with Low Fluorine Content for the Stabilisation of Water-in-CO₂ Microemulsions

The relationship between the tail architecture and performance of hybrid AOT analogue surfactants has been investigated. Three hybrid surfactants were synthesised using hydrocarbon CO₂-philic tails with different levels of chain branching. The performance of each surfactant was investigated via high-pressure phase behaviour, UV-visible spectroscopy, and air–water (a/w) surface tension measurements. Notably, the incorporation of hydrocarbon CO₂-philic tails with a high degree of branching has been found to significantly boost CO₂-philicity, allowing the surfactant to stabilise water-in-CO₂ (w/c) microemulsions at low cloud pressures, P_trans. The newly synthesised hybrid CF2/SIS1 (sodium (4H, 4H, 5H, 5H, 5H-pentafluoropenyl-5,7,7-trimethyl-2-(1,3,3-trimethyl-buthyl)-octyl)-2-sulfosuccinate) is a CO₂-philic surfactant that contains the lowest amount of fluorine (15.01 wt%) and exhibits the highest efficiency of any di-chain surfactant to date. High-pressure phase behaviour studies provided a maximum water-to-surfactant molar ratio (w_max) of w_max = 39, which is usually only observed from surfactants with long fluorocarbon chains. The present results are beneficial for expanding the pool of economical, effective, and efficient surfactants available for CO₂-based technology.