Lyotropic nematic phases of double chain surfactants
Polarization microscopy, 2H-NMR measurements, surface alignment and alignment in magnetic fields were utilized to look for nematic systems within a selection of N-alkyl-N,N-dimethyl-N-hexadecyl ammonium bromide surfactants. Three binary lyotropic nematic systems are reported which consist of rodlike micelles with positive anisotropy of the diamagnetic susceptibility Δξ and negative briefringence: cetyltrimethyl ammonium bromide (CTAB)/water; N,N-dimethyl-N-ethyl-N-hexadecyl ammonium (C16C2DMABr)/water and N-butyl-N,N-dimethyl-N-hexadecyl ammonium bromide (C16C2DMABr)/water. The ternary systems CTAB/decanol/water and C16C2DMABr/decanol/water were investigated. In each system, two nematic phases were found, one consisting of rodlike micelles with positive Δξ and negative total birefringence and one consisting of disclike micelles with negative Δξ and positive total birefringence. A region of coexistence between the two nematic phases is reported for both systems. A systematic method of preparation of nematic phases in similar systems is proposed.
Key wordsLyotropic nematic phases 2H-NMR spectroscopy magnetic field
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