Abstract:

Three Gemini quaternary ammonium surfactants containing ester groups in spacers, C₁₂-E_2nO_m-C₁₂ （i.e., C₁₂-E₂O₂-C₁₂, C₁₂-E₄O₃-C₁₂ and C₁₂-E₆O₄-C₁₂）, were synthesized via two-step reaction and characterized by IR, ¹H NMR, ¹³C NMR and HRMS. The effects of spacer length on the self-aggregation, emulsifying, foaming and wetting properties of C₁₂-E_2nO_m-C₁₂ were investigated. Their corresponding monomer dodecyltrimethylammonium chloride （DTAC） was also investigated for comparison. The results showed that, the critical micelle concentration （cmc） values of C₁₂-E₂O₂-C₁₂, C₁₂-E₄O₃-C₁₂ and C₁₂-E₆O₄-C₁₂ were 0.815, 0.152 and 0.044 2 mmol/L, respectively, which were significantly lower than that of DTAC （10.25 mmol/L）. Among these three Geminis, it was found that the cmc values of C₁₂-E_2nO_m-C₁₂ decreased with increasing spacer length. The phase separation time for evaluating the emulsifying abilities of C₁₂-E₂O₂-C₁₂, C₁₂-E₄O₃-C₁₂ and C₁₂-E₆O₄-C₁₂ were 336, 492 and 682 s, respectively; the wetting time of C₁₂-E₂O₂-C₁₂, C₁₂-E₄O₃-C₁₂ and C₁₂-E₆O₄-C₁₂ were 79, 70 and 64 s, respectively; therefore, C₁₂-E_2nO_m-C₁₂ exhibited excellent emulsifying and wetting properties compared with DTAC （the phase separation time was 116 s and the wetting time was 87 s）. Moreover, C₁₂-E_2nO_m-C₁₂ also had better foaming ability and foam stability than DTAC. The emulsifying, foaming, foam-stabilizing and wetting abilities of C₁₂-E_2nO_m-C₁₂ were increased with the increase of spacer length.

Key words: ester, spacer, Gemini surfactant, quaternary ammonium, surface activity, emulsifying property