Abstract:

p-Perfluorononenyloxy benzene sulfonate(C₉F₁₇OC₆H₄SO₃Na, OBS) a low-cost fluorinated surfactant. However, its surface activity is poor. In this work, OBS was mixed with different cationic hydrogenated surfactants, namely C_nNR[C_nH_2n+1N(CH₃)₃Br(C_nNM, n=8, 10) and C_nH_2n+1N(CH₂CH₃)₃Br(C_nNE, n=8, 10, 12)]. The effects of the molar ratio of OBS to C_nNR, the hydrophobic chain length and the headgroup size of C_nNR(R=M or E) on the critical micelle concentration(cmc), the minimum surface tension(γ_cmc), the maximum surface amount adsorbed(Γ_tm) and the limited surface area per molecule(A_min) for the mixtures of the cationic-anionic hydrogenated-fluorinated surfactants were investigated. The results showed that, after mixed with C_nNR, both the cmc and γ_cmc of the system were greatly lowered, i.e. the efficiency was totally enhanced. The OBS-C₈NE surfactant mixtures with molar ratio of 1:1 showed the best surface activity, i.e. the lowest cmc and γ_cmc, compared with the OBS-C₈NE mixtures with other molar ratios. Meanwhile, when the molar ratio was apart from equimolarity, the cmc of OBS-excess systems were smaller than that of C₈NE-excess systems, but the γ_cmc was not found to be significantly changed. Compared with single surfactant systems, the Γ_tm for the mixtures of OBS-C₈NE was significantly increased and the A_min was significantly decreased. When OBS was mixed with C_nNE with different alkyl chain length, the sequence of cmc for the mixtures was C₈NE>C₁₀NE>C₁₂NE. It suggested that the increase of hydrophobic chain length of C_nNE would induce the decrease of cmc of the mixtures. When the headgroup size of C_nNR(n=8, 10) in the mixture was changed from —triethylammonium to —trimethylammonium, no significant change of the surface activity was found for the mixtures.

Key words: Cationic-anionic surfactant, Surface tension, Fluorocarbon surfactant, Surface activity, Hexafluoropropene trimer