Three Gemini quaternary ammonium surfactants containing ester groups in spacers, C12-E2nOm-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-E2nOm-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-E2nOm-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-E2nOm-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-E2nOm-C12 also had better foaming ability and foam stability than DTAC. The emulsifying, foaming, foam-stabilizing and wetting abilities of C12-E2nOm-C12 were increased with the increase of spacer length.
