Aggregation behavior of partially fluorinated Gemini surfactants in aqueous solution: Effect of headgroups

• PFGS with same hydrophobic group and different headgroups were synthesized.
• 2C6FC3-Sul has higher surface activity than that of 2C6FC3-Me and 2C6FC3-Me.HCl.
• The cmc values for 2C6FC3-Me decrease then increase with the addition of NaCl.

The aggregation behavior of partially fluorinated Gemini surfactants (PFGS) with different headgroups, namely, N,N′-bis[dimethyl-(3-perfluorohexyl-2-hydroxypropyl)ammonium] hexane iodide (2C6FC3-Me), N,N′-bis(3-perfluorohexyl-2-hydroxypropyl) hexylenediamine hydrochloride (2C6FC3-Me.HCl) and N,N′-bis(3-perfluorohexyl-2-hydroxypropyl)-N,N′-dipropanesulfonylhexylenediamine (2C6FC3-Sul) in aqueous solution, were investigated through surface tension and electric conductivity measurements. The surface tension was measured as a function of the concentration at 25, 35 and 45 °C, while the electric conductivity was measured at 25, 30, 35, 40 and 45 °C. The effect of NaCl on the surface activity was also investigated. In addition, the maximum surface excess concentration (Γmax) and minimum surface area/molecule (Amin) at the air/water interface were estimated by using the Gibbs adsorption isotherm. It was found that the surface activity of 2C6FC3-Sul was superior to that of 2C6FC3-Me and 2C6FC3-Me.HCl. Moreover, thermodynamic parameters (ΔGagg0, ΔHagg0, −TΔSagg0) indicated that the aggregation formation of 2C6FC3-Me.HCl and 2C6FC3-Sul was a process of entropy driving, while the aggregation formation of 2C6FC3-Me was a process of entropy driving at low temperature and a process of enthalpy driving at high temperature. These results demonstrated that aggregation behavior of partially fluorinated Gemini surfactants were strongly affected by headgroups in aqueous solution.

Aggregation behaviors of three novel fluorinated Gemini surfactants are investigated. The figure surface tension–concentration for 2C6FC3-Me shows that the values of cmc decrease and then increase as the concentration of added Cl− increases.Figure optionsDownload as PowerPoint slide