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We study the effect of purification and impurities on the self-assembly and phase behavior of lyotropic chromonic liquid crystals (LCLCs). LCLC molecules in water stack to form aggregates; then, the elongated nanoaggregates align to make liquid crystalline phases. Utilizing multiple experimental techniques, we unveil impurities in commercial Sunset Yellow FCF (SSY), a representative LCLC, and how the precipitation-based purification promotes the formation of the aggregates and mesophase. We further explore the roles of intrinsic impurities, i.e., byproducts of the SSY synthesis, whose molecular structures are almost identical to that of SSY but differ only in the number and position of sulfonate groups. Combining quantum chemical calculations of molecular structures and experimental investigation of aggregate structures and phase behavior, we propose that the impurities of the planar shapes behave as planar SSY, i.e., participating in aggregate formation, whereas the nonplanar one disrupts the nematic phase. These results highlight the critical roles of the impurities and deepen our understanding of self-assembled aggregates and their aligned mesophases.

Achiral building blocks forming achiral structures is a common occurrence in nature, while chirality emerging spontaneously from an achiral system is usually associated with important scientific phenomena. We report on the spontaneous chiral symmetry-breaking phenomena upon the topographic confinement of achiral lyotropic chromonic liquid crystals in periodically arranged micrometer scale air pillars. The anisotropic fluid arranges into chiral domains that depend on the arrangement and spacing of the pillars. We characterize the resulting domains by polarized optical microscopy, support their reconstruction by numerical calculations, and extend the findings with experiments, which include chiral dopants. Well-controlled and addressed chiral structures will be useful in potential applications like programmable scaffolds for living liquid crystals and as sensors for detecting chirality at the molecular level., Well-addressed chiral domains are generated with achiral lyotropic chromonic liquid crystal materials using periodic air pillars, which can be potentially used for scaffolds for living matters.

Coating-type polarizing films with a high dichroic ratio (DR) and polarization efficiency in the visible region were fabricated using a solution of ternary lyotropic chromonic liquid crystals (LCLCs). Optical characteristics of these anisotropic LCLC polarizing films were then determined. DR increased with increasing LCLC concentrations. Molecular ordering of these LCLCs on a rubbed polyimide (PI) layer increased because LCLC molecules' orientation was enhanced by the dielectric anisotropy effect from rubbing the surface of the PI. In addition, this study demonstrated how the interaction between liquid crystal aggregates and the PI surface with different LCLC solutions correlated with LCLC molecular orientations on the PI which is significantly dependent on whether the coating direction of the LCLC solution was parallel or perpendicular to the PI rubbing direction. It was found that the ordering direction at high LCLC concentrations was determined by shearing direction of the LCLC solution coating, whereas the ordering direction at low LCLC concentrations was governed by the dielectric anisotropy effect from the PI rubbing direction.

Lyotropic chromonic liquid crystals (LCLCs) constitute a unique variety of water-soluble mesogens that spontaneously assemble into elongated aggregates, thereby resulting in the formation of liquid crystal phases depending on the temperature and concentration. The influence of ionic additives on the aggregation of LCLC has been extensively studied, but the molecular mechanisms governing these effects remain unclear. In this investigation, we perform atomistic molecular dynamics simulations of dilute sunset yellow (SSY) LCLC solutions doped with NaCl and MgCl2 salts. Structural and dynamical properties of SSY hydration shells are considerably modified by the partial substitution of their H bonds with sodium/magnesium-sulfonate ion pairs. Although the intermolecular distance of ∼3.4 A between SSY mesogens is preserved regardless of the ionic content, the growing number of ion pairs favors the reduction of the electrostatic repulsion between mesogens, increasing the length of SSY stacks. Moreover, magnesium ...

Amplification of chirality across length scales is a key concept pertinent to many models aiming to unravel the origin of homochirality. Tactoids of lyotropic chromonic liquid crystals formed by DNA, dyes, and other flat ionic molecules in water in the biphasic nematic + isotropic regime turn out to be a particularly relevant system to investigate chirality transfer and amplification. Herein, we present experiments to determine the amplification of chirality by luminescent gold nanoclusters decorated with adenosine monophosphate inducing chiral nematic tactoids formed by disodium cromoglycate in water. Polarized optical microscopy investigations of the induced homochiral tactoids reveal that adenosine monophosphate shows a higher optical activity when bound to the surface of such gold nanoclusters in comparison to free adenosine monophosphate, despite a three-time lower overall concentration. Free adenosine monophosphate also induces the opposite chiral twist both in the bulk nematic phase as shown by induced thin film circular dichroism spectropolarimetry and in the tactoids in comparison to adenosine monophosphate bound to the gold nanocluster. Overall, these experiments demonstrate that lyotropic chromonic liquid crystal tactoids are powerful systems to image and quantify chirality amplification by key biological chiral molecules that would have played a role in the origin of homochirality.

Temperature and composition effects in Sunset Yellow FCF (SSY) aqueous solutions were studied by the 1H, 15N NMR as well as Raman spectroscopy passing through all phase transitions between isotropic phase (I) and chromonic phases—nematic (N) and columnar (M). It was shown that the tautomeric equilibrium in SSY is strongly shifted toward the hydrazone form. The corresponding equilibrium constant pKT = 2.5 was deduced using the density functional theory solvent model density model. The dominance of the hydrazone form was confirmed experimentally using the long-range 1H–15N correlation, widely known as heteronuclear multiple bond correlation. The peak found in the 1H NMR spectra at ca. 14.5 ppm can be attributed to the proton in the intramolecular N–H···O bond. The existence of this signal shows that (i) the growth of the SSY aggregates is accompanied by the segregation of water in the intercolumnar areas with no access for exchange with the N–H protons in the internal layers of the columnar stacks and that ...

Recently, the emergence of spontaneous reflection-symmetry-broken configurations in achiral chromonic liquid crystals confined in cylindrical capillaries with homeotropic anchoring at the cylinder walls was reported, namely, the so-called twisted-escaped radial (TER) and twisted planar polar (TPP) configurations. This new example of spontaneous reflection symmetry breaking in liquid crystals was attributed to the twist elastic modulus, which is known to be unusually small in comparison to the splay and bend moduli in the case of chromonic liquid crystals. We now report the experimental observation of reflection symmetry breaking in cylindrical capillaries in the case of a classical, achiral, and nonchromonic lyotropic liquid crystal forming a nematic phase of disklike micelles orienting homeotropically at the capillary walls. We observed the same chiral TER configuration, as well as a nonplanar twisted polar (TP) configuration. The TP configuration is characterized by two half-unit so-called twist disclinations, where the director twist around the line defects drives the formation of a double helix of the disclinations along the axis of the capillary. Additionally, there is a transverse twist between the two disclination lines with the same handedness as the axial twist. Similarities with and differences from the case of chromonic liquid crystals are discussed; in particular, we examine the conditions under which spontaneous reflection symmetry breaking occurs in the nonchromonic system. It seems that the chiral TER configuration can be stabilized by the presence of point defects.

Lyotropic chromonic liquid crystals are distinct from thermotropic nematics from a fundamental standpoint as the structure of the aggregating columns is a function of both the temperature and concentration. We report on the thermal evolution of orientational order parameters, both the second (=scalar) (⟨P200⟩ (=S)) and fourth (⟨P400⟩) order, of sunset yellow FCF aqueous solutions, measured using polarized Raman spectroscopy for different concentrations. The order parameter increases with the concentration, and their values are high in comparison with those of thermotropic liquid crystals. On the basis of Raman spectroscopy, we provide the strongest evidence yet that the hydrozone tautomer of SSY is the predominant form in aqueous solutions in the isotropic, nematic, and columnar phases, as well as what we believe to be the first measurements of (⟨P400⟩) for this system.

IR-806 is a near-infrared cyanine dye that undergoes a two-step assembly process in aqueous solutions. The final assemblies orientationally order into a liquid crystal at a very low concentration (∼0.6 wt % at room temperature). While the first step of the assembly process is continuous as the dye concentration or temperature is varied (isodesmic), the second step is more abrupt (cooperative). Because the absorption spectrum of IR-806 changes dramatically during the assembly process, careful equilibrium and kinetic absorption experiments are utilized to examine the details of the cooperative second step. These experiments involve changes in both concentration and temperature, allowing a close thermodynamic analysis of the assembly process. Both equilibrium and kinetic investigations reveal that the assembly process is highly cooperative and can be described by multiple models (for example, nucleation and growth) in the highly cooperative limit. The enthalpy associated with the growth process and the activation energy of the rate-limiting step during disassembly are determined. These findings have significant implications for the structure of the assemblies that form the liquid crystal phase in IR-806.

The azo dye, sunset yellow, is a prototypical, chromonic liquid crystal in which assembly in aqueous solution at high volume fraction leads to lyotropic mesophases with a “package of properties distinct in almost every aspect” (Lydon, J. Curr. Opin. Colloid Interface Sci. 2004, 8, 480). In particular, the isotropic to nematic transition in such phases, the consequence of stacking of dye molecules in chains, is difficult to bring into correspondence with athermal theories for rigid rods as well as modifications that consider chain interactions with one another. Chromonic mesogens, small molecules that stack to form lyotropic liquid crystals, prompt structural questions that have yet to be answered; a full understanding of structure should inform colligative properties. Herein, the single crystal structure of a guanidinium salt of the sunset yellow dianion, a known chromonic mesogen, is reported. The compound crystallizes as a dihydrate, tetrahydrofuran solvate in the orthorhombic space group Pnna, with a =...

We report on the homeotropic alignment of lyotropic chromonic liquid crystals (LCLCs). Homeotropic anchoring of LCLCs is difficult to achieve, and this challenge has limited development of applications for LCLCs. In this work, homeotropic alignment is achieved using noncovalent interactions between the LCLC molecules and various alignment layers including graphene, parylene films, poly(methyl methacrylate) films, and fluoropolymer films. The LCLC molecules are unique in that they self-assemble via noncovalent interactions in water into elongated aggregates which, in turn, form nematic and columnar liquid crystal (LC) phases. Here we exploit these same noncovalent interactions to induce homeotropic anchoring of the nematic LCLC. Homeotropic alignment is confirmed by polarized optical microscopy and conoscopy. We also report on novel transient stripe textures that occur when an initial flow-induced planar alignment transforms into the equilibrium homeotropic alignment required by boundary conditions. An understanding of this behavior could be important for switching applications.

IR-806 is a near-infrared cyanine dye that forms assemblies in aqueous solutions which in turn orientationally order into a liquid crystal phase at concentrations as low as 0.5 wt %. Unlike many chromonic liquid crystals, the absorption spectrum of IR-806 changes dramatically with concentration, showing an isodesmic assembly process at lower concentrations followed by a second process at higher concentrations that is not isodesmic. The lower concentration assembly process is characterized by a free energy change per molecule of about 9 k(B)T, not unlike other chromonic systems. However, X-ray scattering measurements suggest that the assemblies that form during the higher concentration process are much larger than what is observed for many chromonic liquid crystals. Although there is a transitional region between the liquid crystal and isotropic phases of 10-15 °C, unlike most chromonic liquid crystals, no biphasic region is observed using polarizing microscopy.

Single-chain surfactants usually emulsify and stabilize oily substances into droplets in an aqueous solution. Here, we report a coassembly system, in which single types of anionic or non-ionic surfactants emulsify a class of water-soluble nonamphiphilic organic salts with fused aromatic rings in aqueous solutions. The nonamphiphilic organic salts are in turn promoted to form droplets of water-based liquid crystals (chromonic liquid crystals) encapsulated by single-chain surfactants. The droplets, stabilized against coalescence by encapsulated in a layer (or layers) of single chain surfactants, are of both nonspherical tactoid (elongated ellipsoid with pointy ends) and spherical shapes. The tactoids have an average long axis of ∼9 μm and a short axis of ∼3.5 μm with the liquid crystal aligning parallel to the droplet surface. The spherical droplets are 5-10 μm in diameter and have the liquid crystal aligning perpendicular to the droplet surface and a point defect in the center. Cationic and zwitterionic surfactants studied in this work did not promote the organic salt to form droplets. These results illustrate the complex interplay of self-association and thermodynamic incompatibility of molecules in water, which can cause new assembly behavior, including potential formation of vesicles or other assemblies, from surfactants that usually form only micelles. These unprecedented tactoidal shaped droplets also provide potential for the fabrication of new soft organic microcapsules.

We use optical and fluorescence microscopy, densitometry, cryo-transmission electron microscopy (cryo-TEM), spectroscopy, and synchrotron X-ray scattering, to study the phase behavior of the reversible self-assembled chromonic aggregates of an anionic dye Sunset Yellow (SSY) in aqueous solutions crowded with an electrically neutral polymer polyethylene glycol (PEG) and doped with the salt NaCl. PEG causes the isotropic SSY solutions to condense into a liquid-crystalline region with a high concentration of SSY aggregates, coexisting with a PEG-rich isotropic (I) region. PEG added to the homogeneous nematic (N) phase causes separation into the coexisting N and I domains; the SSY concentration in the N domains is higher than the original concentration of PEG-free N phase. Finally, addition of PEG to the highly concentrated homogeneous N phase causes separation into the coexisting columnar hexagonal (C) phase and I phase. This behavior can be qualitatively explained by the depletion (excluded volume) effects that act at two different levels: at the level of aggregate assembly from monomers and short aggregates and at the level of inter-aggregate packing. We also show a strong effect of a monovalent salt NaCl on phase diagrams that is different for high and low concentrations of SSY. Upon the addition of salt, dilute I solutions of SSY show appearance of the condensed N domains, but the highly concentrated C phase transforms into a coexisting I and N domains. We suggest that the salt-induced screening of electric charges at the surface of chromonic aggregates leads to two different effects: (a) increase of the scission energy and the contour length of aggregates, and (b) decrease of the persistence length of SSY aggregates., 42 pages, 12 figures

The solution and liquid crystalline phases formed by dissolution of the dye Edicol Sunset Yellow (ESY) in water have been examined using optical microscopy, multinuclear NMR (1H, 2H, 13C, 23Na), and X-ray diffraction. From the solution 1H and 13C spectra (particularly 13C), it is clear that the tautomeric form present in all these phases is the hydrazone, NH, structure, not the usually given azo, OH, form. Two chromonic mesophases occur: a nematic (N) phase at approximately 30-40 wt % and a hexagonal (M) phase at approximately 40-45 wt %. X-ray diffraction data show that the aggregates in the mesophases are single molecule stacks, with a typical spacing of approximately 3.5 angstroms, as expected for these systems. The NMR quadrupole splittings (2H2O, 23Na) are similar to those observed for surfactant lyotropic mesophases, suggesting that there are no water molecules or counter ions that are tightly bound to the ESY aggregates. An unusual feature of the X-ray diffraction pattern of the mesophases is the occurrence of diffuse off-axis reflections at approximately 6.8 angstroms. It is proposed that these arise from a head-to-tail packing of the molecules within the stacks.

Polarizing microscopy, X-ray scattering, and absorption spectroscopy are used to investigate the aggregation process and chromonic liquid crystal of the anionic compound Bordeaux dye, a product of the sulfonation of the dibenzimidazole derivative of naphthalenetetracarboxylic acid. Polarizing microscopy reveals that the liquid crystal phase forms at room temperature when the concentration is only about 6 wt%, a value lower than what is found in many aggregating systems. The X-ray results indicate that the aggregation is via columns, with a cross-sectional area about 2.5 times larger than the individual molecule. Absorption spectroscopy shows a significant change in the absorption spectrum due to aggregation, which is nicely explained by a simple theory of isodesmic aggregation and excitonic coupling between the molecules in an aggregate. The "stacking free energy change" for a molecule in an aggregate relative to a molecule in solution is estimated to be about 9 kBT, a larger value than that found in the one other system where it has been estimated.

We report rheological, X-ray, and dielectric investigations on a chromonic liquid-crystalline system formed by aqueous solutions of a food coloring agent, Sunset Yellow, in the absence and upon addition of salt. The salt-concentration dependence of the steady-state viscosity at low shear rates has a non-monotonic variation and is qualitatively similar to the behavior seen in wormlike micellar systems, a surprising result since chromonic systems are expected to be non-micellar in character. More interestingly, for a particular low concentration of the salt (20 mM), the viscosity increases by 3 orders of magnitude in comparison with that of the pure chromonic material. The dynamic (oscillatory) rheological data bring out features which can be described in terms of a microstructure formation. X-ray and dielectric studies show that certain characters of the aggregates formed by the Sunset Yellow molecules are not altered by the addition of salt.

Chromonic liquid crystals are formed by the addition of aromatic molecules such as disodium chromoglycate (cromolyn) to water. In this study, we investigate the addition of salts to the lyotropic nematic phase of cromolyn aqueous solutions. The addition of sodium and potassium salts shifts the isotropic-nematic phase boundary upward by more than 10 degrees C, so that samples that were isotropic at room temperature are transformed into nematic phases. Salt effects are predominantly dictated by the cation, not the anion, and appear to differ based on cation size. In contrast to small, hydrated cations like sodium, large, weakly hydrated cations such as tetraethylammonium and tetrabutylammonium shift the phase boundary downward, thus stabilizing the isotropic phase at the expense of the nematic one. The phase behavior results are highly correlated with viscosity measurements, with an upward shift in the phase boundary correlating with an increase in solution viscosity and vice versa. We also probe the microstructure in cromolyn-salt solutions, both indirectly by small-angle neutron scattering (SANS) and directly by cryo-transmission electron microscopy (cryo-TEM). The cryo-TEM images show the presence of rodlike aggregates that possibly undergo a higher order aggregation into bundles in the presence of salt.

We use a layer-by layer electrostatic self-assembly technique to obtain in-plane oriented aggregates of mesogenic dye molecules cast from lyotropic chromonic liquid crystals (LCLCs) on mica substrates. The aqueous solutions of dye used for deposition are in the nematic phase. Atomic force microscopy and X-ray photoelectron spectroscopy of the dried film reveal that the LCLC molecules adsorb at the charged substrate preserving ordered aggregates of elongated shape characteristic of the nematic phase in the aqueous solution. These elongated aggregates of LCLC molecules form films with in-plane orientational order and are compositionally distinct from the substrate.

The chromonic liquid-crystalline properties of bis-(N,N-diethylaminoethyl)perylene-3,4,9,10-tetracarboxylic diimide dihydrochloride in an aqueous solution were investigated by polarized light microscopy and 2H NMR spectroscopy. Both techniques indicate a narrow I + N biphasic region and a broad N phase region at concentrations ranging from approximately 6.9 to approximately 30 wt % at room temperature. Optical microscopy indicates that a hexagonal M phase exists at higher concentrations. The variation of the I --N + I and N + I --N transition temperatures with concentration was studied by 2H NMR spectroscopy. Finally, the effects of temperature and concentration on the order parameter of the N phase were investigated by 2H NMR using a tetra-deuterated derivative. A value of 0.97 was obtained for the N phase at its upper concentration limit.

The chromonic lyotropic liquid crystal formed from an aqueous solution of the azo dye C.I. Direct Blue 67 was investigated by means of a temperature-controlled X-ray diffraction technique, polarized optical microscopy, and UV−visible spectroscopy. The dye molecules form columnar aggregates even at low concentrations. The stacking distance of 3.4 A was observed independent of the concentration and temperature. The addition of a small amount of anionic surfactant was found to induce a nematic phase from a more-ordered hexagonal phase and, thus, enhanced the stability of the nematic phase within a wide range of dye concentrations. The cross-sectional diameter of a column was found to be in good agreement with the molecular length of the dye, indicating that the column is comprised of unimolecular stacking.

A simple method to create large areas of in-plane oriented molecular mono- and multilayers is presented. The method is based on layer-by-layer adsorption of polyions and a lyotropic chromonic (nonamphiphilic) liquid crystal, which allows one to orient the molecules uniformly in the plane of deposition. The long-range in-plane orientation of the chromonic molecules determines the unique structural and optical properties of the films. Control of the orientational order allows one to use the films as polarizers, alignment layers, optical compensators, retarders, filters, etc.

The photoinduced optical anisotropy (POA) of novel aqueous azo dye systems which form chromonic mesophases upon addition of methanol or sodium chloride was investigated. The phases were characterized between crossed polarizers. For further characterization rheological and holographic transient relaxation experiments were carried out. Distinctive differences in the hologram formation and decay were found for phases which exhibit the same texture in polarization microscopy. The generated holographic gratings could be assigned to either photoinduced phase transitions or an alignment of optical axes. In the present study we concentrate on a comparison of phases with the same macroscopic birefringence; results are discussed in comparison with models in the literature.

The chromonic mesogens shown were designed to absorb at different wavelengths and yet display chromonic liquid-crystalline properties in a common solvent. Induced orientation of the mixed liquid crystals by a mechanical shearing force followed by evaporation of solvent produced anisotropic solid films that polarize light from about 450 to 890 nm.

Polarizing optical microscopy and X-ray diffraction measurements have been made on liquid crystals formed by two dyes in water. The dyes, one a cyanine dye and the second an azo dye, both form mesophases above ca. 0.2 wt %. Low angle X-ray diffraction data show that the cyanine dye forms a layer (smectic) phase (spacings up to 750 A), while the azo dye forms columnar nematic and hexagonal mesophases. For both dyes the aggregates appear to be rigid and well ordered, giving rise to multiple low angle diffraction peaks (up to 6 orders). The thickness of the layers is equal to the width of one molecule, but the cross section of the columns is equal to about 6 times the dye molecular area. We propose a columnar pipe structure for these phases. The observation of multiple high-angle X-ray diffraction peaks suggests that the molecules are well ordered at short range within the layers and columns. Hence the mesophases have high order at both the molecular and mesoscopic distance scale.