A homologous series of novel zwitterionic gemini surfactants, N,N-Dimethyl-N-[3-(alkyloxy)-2-sulfatepropyl]-alkylammonium (referred to as C(m)EOSAC(n)), were synthesized. One of the hydrophilic groups is a sulfate anion, and the other is an ammonium cation. Their thermotropic liquid crystalline properties were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and variable-temperature X-ray diffraction (XRD). The results were compared with those for bis(quaternary ammonium) gemini amphiphiles with counterions and catanionic surfactants without a spacer. The C(m)EOSAC(n)s were shown to display improved thermal stability and to form a stable smectic A liquid-crystalline phase over a wide temperature region (63 +/- 0.5 degrees C), which can be attributed to weakening the interactions between the surfactant headgroups. The XRD data confirmed that the two chains of molecules were arranged in a cis configuration with respect to the extended N-CH2-CH-SO4 skeleton in both the solid lattice and the mesophases. In addition, the DSC results showed that the dissymmetry of the hydrophobic chains had a slight effect on the melting point and the clearing point of the C(m)EOSAC(n) compounds. The present investigation points the way to developing stable liquid crystalline materials using gemini-type surfactants. (C) 2009 Elsevier Inc. All rights reserved.