Phase transitions in a nematic binary mixture

Abstract

Our objective was to study mixtures of nematic liquid crystals with dissimilar dielectric anisotropies but similar phase properties. Using light scattering and microscopy, we have established the phase boundaries and transition widths of mixtures of 4′-n-pentyl-4-cyanobiphenyl and 4′-methoxybenzylidene-4-butylaniline. In addition to the isotropic-nematic transition, there is a second induced phase for certain concentrations, which we conclude is an induced smectic B phase. Recent theoretical works provide a model for nematic to induced smectic A transition by combining Flory–Huggins and Maier–Saupe–McMillan theories. From our phase transition data and the application of the above theoretical framework, we conclude that there is a possibility of strong interaction between the two mesogens that produces the smectic B phase.

Phase transition and some physical properties of binary mixtures of two nematogenic compounds showing induced smectic phase

“…Such possibility was also proposed earlier [22,23]. Smectic layer spacing as well as average intermolecular distance show minima at x ¼ 0.33, which is in accordance with our observed density variation.…”

Inhomogeneous nematic-isotropic phase transition of a thermotropic liquid crystal doped with iron oxide nanoparticles

“…The N-I transition temperature (T N-I ) of the "IONP-poor" and "IONP-rich" mixtures were measured to be 31.6±0.6 °C and 32.0±0.6 °C, respectively, which had no significant difference with that of pure 5CB (32.5±0.6 °C) in the same type of LC cell. The measured T N-I of pure 5CB showed a full consistence to the previous reports by Parra-Vasquez et al [26] (T N-I = 32±1 °C) and Rauch et al [27] (T N-I = 31.2 °C), where the comparable thickness of LC glass cells were used. In previous works by Rodarte et al [13] and Melton et al [11], the "crystallization" (i.e., I-N transition) of NP-doped disordered 5CB upon cooling was shown to repel the suspended NPs (6 nm-sized quantum dots) from the growing nematic domains to the shrinking isotropic domains.…”

Optical Microscopy, X-Ray Diffraction, and Dielectric Permittivity Studies in Binary Mixtures of Nematogens Showing Induced Smectic Phase

“…Since the layer spacing in all the mixtures is greater than the model molecular lengths of the pure compounds, so there is possibility of formation of molecular association. Such possibility was also proposed earlier [16,17].…”