Lyotropic liquid crystalline phases with a series of N-alkyl-N-methylpiperidinium bromides and water

The lyotropic liquid crystalline (LLC) phases formed by a series of N-alkyl-N-methylpiperidinium bromides (CnPDB, n = 12, 14, 16) in water have been investigated. By using polarized optical microscopy (POM) and small angle X-ray scattering (SAXS) techniques, the normal hexagonal (H-1) and reverse bicontinuous cubic (V-2) LLC phases can be detected with C14PDB/H2O and C16PDB/H2O systems within a large temperature and concentration ranges. In the C12PDB/H2O system, only the H-1 phase is observed. Such differences may be attributed to differences in hydrophobic interactions resulting from their different alkyl chain lengths. The theological results reveal that the H-1 phase formed by C12PDB displays a typical Maxwell behavior, whereas those with C14PDB or C16PDB show gel-like behavior, unlike the traditional cationic surfactants. The obtained results on the LLC phases formed by this new class of piperidinium surfactants supplement the current understanding about nitrogen-containing heterocyclic headgroup-based cationic surfactants and may open their wide potential applications. (C) 2012 Elsevier Inc. All rights reserved.