Effects of the interactions of surfactants/dye and surfactant/drug on the formation of different types of lyotropic nematic phases

Lyotropic nematic liquid crystal phases, a subclass of lyotropic liquid crystals, have continued to attract the attention of many research groups due to the magnetic field sensitivity of their phase directors or optical axes ( n ⃗ ) compared to other liquid crystal phases. Lyotropic nematic phases are divided into two uniaxial (ND, NC) and biaxial (NB) based on their orientations, micelle symmetries or geometries. Lyotropic nematic phase properties of some novel mixtures of dodecyltrimethylammonium bromide (DTMABr)/1-dodecanol (DDeOH)/water, doping with some anionic azo dyes (Sunset Yellow, amaranth, and tartrazine) and a drug molecule disodium cromoglycate (cromolyn, DSCG), were investigated in the present study. The textural analysis of the uniaxial and biaxial nematic phases was performed by a conventional technique, polarizing optical microscopy (POM). Uniaxial-to-biaxial nematic phase transitions were determined from the temperature dependence of the birefringences of the nematic phases via laser conoscopy. Partial phase diagrams of the mixtures were constructed as a function of dyes/drug "molecules' concentrations" 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 dye and drug molecules have a greater effect on (a) the nematic-nematic phase transitions, (b) the biaxial nematic phase domain range in the partial phase diagrams, and (c) micelle shape anisotropy than the conventional inorganic electrolyte ions. Furthermore, dye/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 the dye/drug molecules may have a resonance structure (e.g. DSCG) as a result of the existence of the aromatic parts in their structure, this resonance structure should be considered to investigate their effects on the formation of the lyotropic nematic phases.