Molecular Self-assemblies in Water and Brine and Solution Properties for a Hybrid Fluorocarbon Surfactant

Abstract A novel hybrid fluorinated surfactant, sodium 2-[2-(perfluorohexyl)] acetoxy ethanesulphonate (NaFHAE), was used as a wettability-altering chemical. It was desired to reduce the bound water on sandstone and the capillary pressure for water flooding in superlow-permeability sandstone reservoirs. The critical micelle concentrations (cmcs) of NaFHAE were respectively 0.38 and 0.35 g/L in water and brine with 30 g/L NaCl at 30 °C. At 0.35 g/L in brine, the contact angle was 68.13°, and the surface and interface tensions were 16.70 and 3.43 mN/m, respectively. When 0.2 g/L PS was added to the 0.1 g/L NaFHAE brine, the interface tension decreased sharply from 7.57 to 0.94 mN/m, and the contact angle was unchanged. For the unsalted NaFHAE solution, it was surprising that the addition of PS caused a remarkable increase in the contact angle, especially at 0.1 g/L NaFHAE. The micellization of NaFHAE was entropy-driven, the absolute values of ΔG°m were above 35.00 kJ/mol, and the spontaneity of micellization was strong compared to the hydrocarbon surfactants. The diameters of micelles were primarily 30 nm above the cmc in water. UV and fluorescent probe results revealed that the non-polarity of the hydrophobic micro-environment in micelles was weak for hybrid fluorinated surfactants compared with hydrocarbon surfactants and that the sizes of micelles were also affected slightly by salt.