清洁能源化学与材料实验室知识库

Five cationic CH–CF hybrid surfactants, each of which has a hydrocarbon chain (C_nH_2n+1, n = 8, 10, 12, 14, 16) and a fluorocarbon one (C₆F₁₃), have been synthesized. Taking the advantage of the Grignard reaction and the subsequent quaternization, the hybrid surfactants were obtained with high synthetic yields over 65%. Their structures have been unambiguously confirmed by FTIR, ¹H NMR, ¹⁹F NMR, ¹³C NMR and MS measurements. ¹⁹F NMR revealed that the presence of the chiral carbon center induced a nonequivalent magnetic resonance of the adjacent fluorine nuclei. The aggregation behavior of the hybrid surfactants were investigated by surface tension, conductivity and steady-state fluorescence measurements. Surface tension measurements revealed that the hybrid surfactants exhibited high surface activity. With increasing hydrocarbon chain length, the critical micellar concentration (cmc) decreased while the surface tension at the cmc (γ_cmc) increased. Both the results of conductivity and surface tension measurements showed there exists a stepwise aggregation behavior for the hybrid surfactants with n = 8 and 10. Steady-state fluorescence measurements showed fairly good agreement with the results obtained from conductivity and surface tension measurements. Evaluation of the thermodynamic parameters (⊿G⁰_m, ⊿H⁰_m, ⊿S⁰_m) showed that the aggregate formation of the hybrid surfactants with n < 16 is enthalpy-driven at low temperature, which turns to entropy-driven at high temperature. While the aggregate formation of the hybrid surfactant with n = 16 is entropy-driven within all the investigated temperature ranges.