SOLUBILIZATION OF N-ALKYLPYRIDINIUM IONS IN ANIONIC NEMATIC LYOMESOPHASES

Deuterium quadrupole splittings from the aromatic ring of a series of linear N-alkylpyridinium-d(5) ions, with alkyl chains from 1 to 16 car bon atoms, were measured using H-2-NMR spectroscopy. The pyridinium io ns, 10% deuteriated in the aromatic ring, were dissolved in nematic an ionic lyomesophases prepared from sodium decyl sulfate (SDS) and cesiu m decyl sulfate (CsDS). With these splittings, the two order parameter s that completely describe the average orientation of the aromatic rin g with respect to the magnetic field were calculated. The added pyridi nium ions have a dramatic effect on the mobility of the CsDS mesophase components. The smaller N-methyl and N-ethylpyridinium ions, C-1 and C-2, have a disruptive effect on the integrity of the mesophase, C-3 a nd C-4 do not have an appreciable effect, and the larger ones, C-5 to C-12, show the opposite effect, increasing the order of the system wit h the length of the alkyl chain. This phenomenon, not observed in the SDS mesophase, may be attributed to differences in charge distribution between both surfaces. This interpretation is supported by estimation of the degrees of dissociation and first cmc of SDS and CsDS using co nductometric measurements. The results could also be explained if the CsDS mesophase was near to a phase transition and stabilized by the ad ded ions.