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 (C(n)PDB, 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 C(14)PDB/H(2)O and C(16)PDB/H(2)O systems within a large temperature and concentration ranges. In the C(12)PDB/H(2)O 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 rheological results reveal that the H(1) phase formed by C(12)PDB displays a typical Maxwell behavior, whereas those with C(14)PDB or C(16)PDB 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.