Origin of lyotropic liquid crystalline mesophase formation and liquid crystalline to mesostructured solid transformation in the metal nitrate salt-surfactant systems

Abstract

The zinc nitrate salt acts as a solvent in the ZnX-C12EO10 (ZnX is [Zn(H2O)6](NO3)2 and C12EO10 is C12H25- (OCH2CH2)10OH) 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 C and undergoes a phase change into a solid mesostructured salt upon cooling below -52 C; no phase separation is observed down to -190 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(V1)-2D hexagonal(H1) - a mixture of 2D hexagonal and micelle cubic(H1 þ I)- micelle cubic(I)-micelle(L1) 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.