Transparent nematic phase in a liquid-crystal-based microemulsion

Abstract

Complex fluids are usually produced by mixing together several distinct components, the interactions between which can give rise to unusual optical and rheological properties of the system as a whole. For example, the properties of microemulsions (composed of water, oil and surfactants) are determined by the microscopic structural organization of the fluid that occurs owing to phase separation of the component elements. Here we investigate the effect of introducing an additional organizing factor into such a fluid system, by replacing the oil component of a conventional water-in-oil microemulsion with an intrinsically anisotropic fluid--a nematic liquid crystal. As with the conventional case, the fluid phase-separates into an emulsion of water microdroplets (stabilized by the surfactant as inverse micelles) dispersed in the 'oil' phase. But the properties are further influenced by a significant directional coupling between the liquid-crystal molecules and the surfactant tails that emerge (essentially radially) from the micelles. The result is a modified bulk-liquid crystal that is an ordered nematic at the mesoscopic level, but which does not exhibit the strong light scattering generally associated with bulk nematic order: the bulk material here is essentially isotropic and thus transparent.

Colloidal interactions in two-dimensional nematics

“…Since the temperature changes the anisotropic properties of the host fluid, the dispersed particles exhibit a rich variety of collective behaviors, leading to unexpected phase diagrams [2]. Depending on the details of the system, chain-like [3,4], crystal [5] or cellular [6] structures have been observed.…”

Does transparent nematic phase exist in 5CB/DDAB/water microemulsions? From the viewpoint of temperature dependent dielectric spectroscopy

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] What make them highly intriguing are the novel properties arising from the elastic distortion of LCs induced by the dispersed particles or droplets and fascinating colloidal structures attributed to the interparticle interaction mediated by the elastic distortions of the LC host. These new properties and structures are generally absent in conventional LCs and colloidal systems but important in technological application and fundamental science.…”

“…The phase behavior and phase composition of this LCM have been intensively studied in recent years by many methods, 5,10,16,19,20 but controversy still remains. First reported by Yamamoto and Tanaka, 5 this system exhibits on cooling two-phase transformations: a transition from isotropic to a new phase called "transparent nematic" (TN) phase occurs first; with further cooling, a phase separation occurs and leads to a coexistence of bulklike nematic phase and TN phase. The TN phase is macroscopically transparent but locally ordered on scales of several nanometers, which became the focus of the controversy.…”

Surface tension and capillary waves at the nematic-isotropic interface in ternary mixtures of liquid crystal, colloids, and impurities

“…This separation is due ͑only in part, as we shall see later͒ to the distortions of the director field cost energy. [12][13][14][15][16][17] It turns out that the first studies have focused on dispersions of Ϸ200 nm size poly͑methyl methacrylate͒ ͑PMMA͒ spheres in 4Ј-pentyl-4-cyanobiphenyl ͑5CB͒ or N-4-methoxybenzylidene-4Ј-butylaniline. Microscopic observations have shown that below the nematic-toisotropic phase transition temperature, the two phases coexist by forming a three-dimensional network which gives to the mixture the consistency of a soft cellular solid.…”