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 (H1) and reverse bicontinuous cubic (V2) 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 H1 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 H1 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.

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► Lyotropic liquid crystalline mesophases are formed by N-alkyl-N-methylpiperidinium (CnPDB) bromides.
► Comparisons of the phase behavior of CnPDB are made with other N-heterocyclic headgroup surfactants.
► Unusual rheological behavior for hexagonal phases is found for longer chain CnPDB systems.