Origin of Lyotropic Liquid Crystalline Mesophase Formation and Liquid Crystalline to Mesostructured Solid Transformation in the Metal Nitrate Salt-Surfactant Systems

The zinc nitrate salt acts as a solvent in the ZnX-C12EO10 (ZnX is [Zn(H2O)(6)](NO3)(2) and C12EO10 is C12H25(OCH2CH2)(10)OH) lyotropic liquid crystalline (LLC) mesophase with a drastic dropping on the melting point of ZnX. The salt surfactant LLC mesophase is stable down to -52 degrees C and undergoes a phase change into a solid mesostructured salt upon cooling below -52 degrees C; no phase separation is observed down to -190 degrees C. The ZnX-C12EO10 mesophase displays a usual phase behavior with an increasing concentration of the solvent (ZnX) in the media with an order of bicontinuous cubic(V-1)-2D hexagonal(H-1) - a mixture of 2D hexagonal and micelle cubic(H-1 + I)-micelle cubic(I)-micelle(L-1) phases. The phase behaviors, specifically at low temperatures, and the first phase diagram of the ZnX-C12EO10 system was investigated using polarized optical microscopy (POM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR), and Raman techniques and conductivity measurements.