Abstract
A homologous series of novel zwitterionic gemini surfactants, N, N-dimethyl- N-[3-(alkyloxy)-2-sulfate-propyl]-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 °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–CH 2–CH–SO 4 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.
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