Observation of Two Biaxial Nematic Mesophases in the Tetradecyltrimethylammonium Bromide/Decanol/Water System

• Published in: Langmuir 2003-02, Vol.19 (4), p.1127-1132
• Main Authors: de Melo Filho, Antonio A, Laverde, Antonio, Fujiwara, Fred Y
• Format: Article
• Language: English
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la026618z

The phase diagram of the nematic mesophases present in the tetradecyltrimethylammonuim bromide/n-decanol/water system was determined. Two distinct biaxial nematic mesophases with opposite diamagnetic and optical anisotropies were identified using 2H NMR spectroscopy and optical microscopy with polarized light. Two nematic biaxial phases were observed in a very narrow region between the two uniaxial nematic mesophases. The sequence of phase changes, hexagonal−calamitic NC−biaxial NBX +−biaxial NBX -−discotic ND−lamellar mesophases, was observed with increasing decanol content. The phase transition between the two biaxial mesophases is first order, while the phase transitions between the NC and NBX + and the NBX -−ND mesophases are second order. The order parameters of the ionic headgroup of the surfactant, determined from the 2H quadrupolar splittings, indicate that the average micelle size decreases with the decanol content in the NC and NBX + mesophases and increases with the decanol content in the NBX - and ND mesophases.