A　homologous　series　of　novel　zwitterionic　gemini　surfactants,　N,N-dimethyl-N-[3-(alkyloxy)-2-sulfate-propyl]-alkylammonium　(referred　to　as　CmEOSACn),　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　CmEOSACns　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-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　CmEOSACn　compounds.　The　present　investigation　points　the　way　to　developing　stable　liquid　crystalline　materials　using　gemini-type　surfactants.　©　2009　Elsevier　Inc.　All　rights　reserved.