Properties of the uniaxial and biaxial nematic phases of the dodecyltrimethylammonium bromide/1-dodecanol/water lyotropic mixture including azo dye and drug molecules

Lyotropic nematic phase properties of novel mixtures of dodecyltrimethylammonium bromide (DTMABr)/1-dodecanol (DDeOH)/water, doping with anionic azo dyes (amaranth and tartrazine) and a drug molecule disodium cromoglycate (cromolyn, DSCG), were investigated. The textures of the uniaxial and biaxial nematic phases were observed by polarizing optical microscopy (POM). Uniaxial-to-biaxial nematic phase transitions were determined from the temperature dependence of the birefringences via laser conoscopy. Partial phase diagrams of the mixtures were constructed as a function of concentrations of dyes and drug molecules by combining the POM and laser conoscopy results. Small-angle X-ray scattering (SAXS) was performed to evaluate micellar structure parameters. The results indicate that those dyes and drug molecules have a greater effect on (a) the nematic-nematic phase transition temperatures, (b) the biaxial-nematic phase-domain range in the partial phase diagrams, and (c) micelle-shape anisotropy, comparing to the addition of other conventional inorganic electrolyte ions. Furthermore, dye and drug molecules may be sequenced in the Hofmeister series of ions, considering the number of ionic groups in their molecular structures and also the chaotropic and/or kosmotropic degrees of the ionic groups. Since these molecules may have a resonance structure (e.g. DSCG), as a result of the existence of the aromatic parts in their structures, this resonance structure should be considered to investigate their effects on the stabilization of the lyotropic nematic phases.