Formation of micellar nematic phases from surfactants and aqueous orthophosphoric acid
Özet
It is shown that aqueous orthophosphoric acid can be used as a solvent for cationic surfactants to form micellar nematics which align spontaneously in magnetic fields. The cationic surfactants investigated were decylammonium chloride (DACl) and decylammonium dihydrogen phosphate (DAPH2). The percentage of pure H3PO4 in the nematic phases of DACl could be varied from 10 to 70 per cent while DAPH2 gave a nematic phase in a narrow range with 60 per cent H3PO4. As the percentage of pure H3PO4 in the DACl nematic phase increased, the 23Na quadrupolar splitting decreased; this was attributed to an alteration in the binding sites of these systems. 31P N.M.R. of H3PO4 in DACl and DAPH2 nematic phases gave a symmetric singlet indicating that the chemical shift of H3PO4 in these systems is isotropic. A mixture of the anionic surfactants, sodium decylsulphate (SDS) with 10 per cent H3PO4 gave a micellar nematic phase as a result of a replacement reaction in which orthophosphoric acid monodecylester (PDE) was produced. The director of the nematic phases of the DACl, DAPH2 and SDS systems aligned perpendicular to the magnetic field direction (negative diamagnetic anisotropy, ?? < 0). The 31P N.M.R. spectrum of PDE in the SDS nematic phase gave an asymmetric singlet which is assumed to result from the 31P chemical shift anisotropy. Solutions of n-decanol and 85 per cent H3PO4 gave viscous birefringent phases which contained an isotropic phase and a lamellar phase. © 1989 Taylor & Francis Group, LLC.
