Lyotropic Chromonic Liquid Crystals Research Articles

Flow-induced periodic chiral structures in an achiral nematic liquid crystal

Supramolecular chirality typically originates from either chiral molecular building blocks or external chiral stimuli. Generating chirality in achiral systems in the absence of a chiral input, however, is non-trivial and necessitates spontaneous mirror symmetry breaking. Achiral nematic lyotropic chromonic liquid crystals have been reported to break mirror symmetry under strong surface or geometric constraints. Here we describe a previously unrecognised mechanism for creating chiral structures by subjecting the material to a pressure-driven flow in a microfluidic cell. The chirality arises from a periodic double-twist configuration of the liquid crystal and manifests as a striking stripe pattern. We show that the mirror symmetry breaking is triggered at regions of flow-induced biaxial-splay configurations of the director field, which are unstable to small perturbations and evolve into lower energy structures. The simplicity of this unique pathway to mirror symmetry breaking can shed light on the requirements for forming macroscopic chiral structures.

Confinement twists achiral liquid crystals and causes chiral liquid crystals to twist in the opposite handedness: cases in and around sessile droplets.

We study the chiral symmetry breaking and metastability of confined nematic lyotropic chromonic liquid crystals (LCLCs) with and without chiral dopants. The isotropic-nematic coexistence phase of the LCLC renders two confining geometries: sessile isotropic (I) droplets surrounded by the nematic (N) phase and sessile nematic droplets immersed in the isotropic background. In the achiral system with no dopants, LCLC's elastic anisotropy and topological defects induce a spontaneous twist deformation to lower the energetic penalty of splay deformation, resulting in spiral optical textures under crossed polarizers both in the I-in-N and N-in-I systems. While the achiral system exhibits both handednesses with an equal probability, a small amount of the chiral dopant breaks the balance. Notably, in contrast to the homochiral configuration of a chirally doped LCLC in the bulk, the spiral texture of the disfavored handedness appears with a finite probability both in the I-in-N and N-in-I systems. We propose director field models explaining how chiral symmetry breaking arises by the energetics and the opposite-twist configurations exist as meta-stable structures in the energy landscape. These findings help us create and control chiral structures using confined LCs with large elastic anisotropy.

A computational study of nematic core structure and disclination interactions in elastically anisotropic nematics.

A singular potential method in the Q tensor order parameter representation of a nematic liquid crystal is used to study the equilibrium configuration of a disclination dipole. Unlike the well studied isotropic limit (the so called one constant approximation), we focus on the case of anisotropic Frank elasticity (bend/splay elastic constant contrast). Prior research has established that the singular potential method provides an accurate description of the tensor order parameter profile in the vicinity of a disclination core of a highly anisotropic lyotropic chromonic liquid crystal. This research is extended here to two interacting disclinations forming a dipole configuration. The director angle is shown to decay in the far field inversely with distance to the dipole as is the case in the isotropic limit, but with a different angular dependence. Therefore elastic constant anisotropy modifies the elastic screening between disclinations, with implications for the study of ensembles of defects as seen, for example, in active matter in the extended system limit.

Research progress on performance regulation of lyotropic chromonic liquid crystals

Research progress on performance regulation of lyotropic chromonic liquid crystals

Shear-induced flow and dynamics of the nematic phase of Sunset Yellow lyotropic chromonic liquid crystal

ABSTRACT Fundamental understanding of rheological properties of lyotropic chromonic liquid crystals is inadequate compared to their thermotropic counterparts in spite of the growing interest in these materials. Here, we investigate the rheological properties of a lyotropic chromonic nematic liquid crystal (LCLC), prepared by dissolving 32 wt% of Sunset Yellow (SSY) in water. The flow curves (stress-strain rate, σ − γ ˙ ) at different temperatures exhibit three flow regimes R1, R2 and R3, respectively. At room temperature, in R1 ( γ ˙ < γ ˙ cl ) and R3 ( γ ˙ > γ ˙ cu ) the sample exhibits Newtonian flow behaviour ( σ ∝ γ ˙ ), whereas, in R2 ( γ ˙ cl < γ ˙ < γ ˙ cu ), it shows a power-law dependence ( σ ∼ γ ˙ β ). With increasing shear rate the change of stress from R1 to R2 is continuous, whereas the change is discontinuous from R2 to R3. We observe stress fluctuations under steady shear in regime R2 similar to those reported in worm-like micellar systems and in thermotropic twist-bend nematic liquid crystals. The non-monotonic flow behaviour and the stress dynamics are corroborated using in situ rheo-microscopy.

Spatio-temporal programming of lyotropic phase transition in nanoporous microfluidic confinements

HypothesisThe nanoporous polydimethylsiloxane (PDMS) surfaces of a rectangular microfluidic channel, selectively uptakes water molecules, concentrating the solute molecules in an aqueous phase, that could drive phase transitions. Factors such as surface wettability, channel geometry, the surface-to-volume ratio, and surface topography of the confinements could play a key role in tuning the phase transitions spatio-temporally. ExperimentsUsing a lyotropic chromonic liquid crystal as model biological material, confined within nanoporous microfluidic environments, we study molecular assembly driven by nanoporous substrates. By combining timelapse polarized imaging, quantitative image processing, and a simple mathematical model, we analyze the phase transitions and construct a master diagram capturing the role of surface wettability, channel geometry and embedded topography on programmable lyotropic phase transitions. FindingsIntrinsic PDMS nanoporosity and confinement cross-section, together with the imposed wettability regulate the rate of the N-M phase transition; whereas the microfluidic geometry and embedded topography enable phase transition at targeted locations. We harness the emergent long-range order during N-M transition to actuate elasto-advective transport of embedded micro-cargo, demonstrating particle manipulation concepts governed by tunable phase transitions. Our results present a programmable physical route to material assembly in microfluidic environment, and offer a new paradigm for assembling genetic components, biological cargo, and minimal synthetic cells.

Sunset Yellow Confined in Curved Geometry: A Microfluidic Approach.

The behavior of lyotropic chromonic liquid crystals (LCLCs) in confined environments is an interesting research field that still awaits exploration, with multiple key variables to be uncovered and understood. Microfluidics is a highly versatile technique that allows us to confine LCLCs in micrometric spheres. As microscale networks offer distinct interplays between the surface effects, geometric confinement, and viscosity parameters, rich and unique interactions emerging at the LCLC-microfluidic channel interfaces are expected. Here, we report on the behavior of pure and chiral doped nematic Sunset Yellow (SSY) chromonic microdroplets produced through a microfluidic flow-focusing device. The continuous production of SSY microdroplets with controllable size gives the possibility to systematically study their topological textures as the function of their diameters. Indeed, doped SSY microdroplets produced via microfluidics, show topologies that are typical of common chiral thermotropic liquid crystals. Furthermore, few droplets exhibit a peculiar texture never observed for chiral chromonic liquid crystals. Finally, the achieved precise control of the produced LCLC microdroplets is a crucial step for technological applications in biosensing and anticounterfeiting.

Luminescent DNA-origami nano-rods dispersed in a lyotropic chromonic liquid crystal

ABSTRACTAnisometric DNA nanoparticles with precisely tailored size and shape are prepared by three-dimensional folding of DNA – DNA origami – marked with a fluorescent intercalating dye (YOYO-1), stabilised with silica, and dispersed in a lyotropic chromonic liquid crystal (an aqueous solution of disodium cromoglycate). Observations by total internal reflection fluorescence microscopy indicate that the luminescent nanoparticles are stable in the liquid crystal dispersion and accumulate at the positions of point defects in the liquid crystal director field. The observations indicate that silica-stabilisation of the nanoparticles prevents the dye from leaking into the liquid crystal host and that the luminescent particles assemble at disclinations.

Agarose hydrogels reinforced by chromonic aggregates

We report the mechanical properties of agarose hydrogels enhanced by the introduction of a lyotropic chromonic liquid crystal, Sunset Yellow FCF (SSY). The soft, fibre-like structures of the chromonic aggregates interact with and reinforce the hydrogel networks, creating soft composites with maximum stress, fracture strain, and stiffness (Young’s modulus) 30 to 40% larger than those of pure agarose hydrogels.

Cover Feature: Chirality Transfer from an Innately Chiral Nanocrystal Core to a Nematic Liquid Crystal 2: Lyotropic Chromonic Liquid Crystals (ChemPhysChem 3/2023)

The Cover Feature illustrates the formation of homochiral nematic lyotropic chromonic liquid crystal tactoids formed by disodium cromoglycate in water by the addition of cromoglycate surface-modified cellulose nanocrystals (CNCs) as chiral solutes. Using CNCs with an inherently chiral core reveals that biorenewable chiral solutes can serve as suitably powerful and increasingly multipurpose chiral additives. More information can be found in the Research Article by Diana P. N. Gonçalves, Timothy Ogolla, and Torsten Hegmann.

Aggregation phenomena in lyotropic chromonic liquid crystals

We study the aggregation phenomenon in lyotropic chromonic liquid crystals as the molecular concentration changes and condensing agents are added into the system. Using properties of the critical points of the Oseen–Frank energy of a nematic liquid crystal, combined with the geometric constraints of the hexagonal columnar chromonic phases, we show that the minimizers of the total energy are topologically equivalent to tori, in agreement with available experimental evidence on chromonic liquid crystals and DNA condensates, in viral capsids as well as in free solution. We model the system as bi-phasic, consisting of liquid crystal molecules and water, and postulate the total energy as the sum of the Flory–Huggins energy of mixing together with the bending and surface tension contributions of the liquid crystal. Two types of problems are considered, one related to finding the optimal shape of a torus, once the phase separation has occurred, and the second one that models the conditions leading to molecular aggregation. This work follows recent experimental investigations, but without addressing the topological properties of the toroidal nuclei observed and focusing on how the liquid crystal order competes with the aggregation phenomenon.

Foreword of the special issue: Nonlinear models and tools in economics, finance and social sciences

We study the aggregation phenomenon in lyotropic chromonic liquid crystals as the molecular concentration changes and condensing agents are added into the system. Using properties of the critical points of the Oseen–Frank energy of a nematic liquid crystal, combined with the geometric constraints of the hexagonal columnar chromonic phases, we show that the minimizers of the total energy are topologically equivalent to tori, in agreement with available experimental evidence on chromonic liquid crystals and DNA condensates, in viral capsids as well as in free solution. We model the system as bi-phasic, consisting of liquid crystal molecules and water, and postulate the total energy as the sum of the Flory–Huggins energy of mixing together with the bending and surface tension contributions of the liquid crystal. Two types of problems are considered, one related to finding the optimal shape of a torus, once the phase separation has occurred, and the second one that models the conditions leading to molecular aggregation. This work follows recent experimental investigations, but without addressing the topological properties of the toroidal nuclei observed and focusing on how the liquid crystal order competes with the aggregation phenomenon.

Dendritic patterns from shear-enhanced anisotropy in nematic liquid crystals.

Controlling the growth morphology of fluid instabilities is challenging because of their self-amplified and nonlinear growth. The viscous fingering instability, which arises when a less viscous fluid displaces a more viscous one, transitions from exhibiting dense-branching growth characterized by repeated tip splitting of the growing fingers to dendritic growth characterized by stable tips in the presence of anisotropy. We controllably induce such a morphology transition by shear-enhancing the anisotropy of nematic liquid crystal solutions. For fast enough flow induced by the finger growth, the intrinsic tumbling behavior of lyotropic chromonic liquid crystals can be suppressed, which results in a flow alignment of the material. This microscopic change in the director field occurs as the viscous torque from the shear flow becomes dominant over the elastic torque from the nematic potential and macroscopically enhances the liquid crystal anisotropy to induce the transition to dendritic growth.

Spontaneous Twisting of Achiral Hard Rod Nematics.

Since Onsager's seminal work, hard rods have been taken as a prototype of nematic liquid crystals, characterized by uniaxial order and a uniform director field as a ground state. Here, using Onsager theory to calculate the free energy in the presence of arbitrary deformations, we find that hard rod nematics have an intrinsic tendency to twist around their ordering axis (double twist), driven by a mechanism in which the orientational fluctuations of particles play a key role. The anisotropic hard core potential used here is arguably the simplest form of interaction able to originate spontaneous breaking of mirror symmetry in a 3D fluid. Our results are discussed in relation to the recent discovery of a double twisted ground state in cylindrically confined lyotropic chromonic liquid crystals.

Statement of Retraction: Optical and Thermal Studies on Lyotropic Chromonic Liquid Crystals in Nematic and Biphasic Regions

Statement of Retraction: Optical and Thermal Studies on Lyotropic Chromonic Liquid Crystals in Nematic and Biphasic Regions

Statement of Retraction: Optical Characterization of Lyotropic Chromonic Liquid Crystals

Statement of Retraction: Optical Characterization of Lyotropic Chromonic Liquid Crystals

Label-free optical and electrical immunoassays based on lyotropic chromonic liquid crystals: Implications of real-time detection and kinetic analysis

Conventional liquid crystal (LC)-based biosensors utilize predominantly thermotropic LCs as the signal-transducing media, which are less environmentally sustainable compared with lyotropic counterparts. In this study, the nematic phase of the anionic azo dye sunset yellow (SSY), a type of lyotropic chromonic liquid crystals (LCLCs), was employed in the optical and electrical biosensing of bovine serum albumin (BSA) and the cancer biomarker CA125. The optical response observed under a polarizing optical microscope was quantified by image analysis, taking advantage of the specific absorption of SSY. The electrical response derived from the dielectric spectra of SSY provided a new alternative for quantitative bioassay based on nematic LCLCs. The limit of detection (LOD) of the optical and electrical protein assay was ∼10−11- and ∼10−10-g/ml BSA, respectively, whereas that of the optical and electrical immunoassay was 5.97 × 10−11 and 6.02 × 10−12 g/ml for CA125, respectively. Moreover, real-time monitoring and kinetic analysis, which are hardly achievable for the hydrophobic thermotropic LCs, were demonstrated by dispersing CA125 in nematic SSY and subsequently recording the optical response over time during the specific binding between CA125 and the immobilized anti-CA125 antibody. Results from this study further the potential of nematic LCLCs in biosensing, especially in dielectric and real-time detection.

Chirality Transfer from an Innately Chiral Nanocrystal Core to a Nematic Liquid Crystal 2: Lyotropic Chromonic Liquid Crystals.

The importance of and the difference between molecular versus structural core chirality of substances that form nanomaterials, and their ability to transmit and amplify their chirality to and within a surrounding condensed medium is yet to be exactly understood. Here we demonstrate that neat as well as disodium cromoglycate (DSCG) surface-modified cellulose nanocrystals (CNCs) with both molecular and morphological core chirality can induce homochirality in racemic nematic lyotropic chromonic liquid crystal (rac-N-LCLC) tactoids. In comparison to the parent chiral organic building blocks, D-glucose, endowed only with molecular chirality, both CNCs showed a superior chirality transfer ability. Here, particularly the structurally compatible DSCG-modified CNCs prove to be highly effective since the surface DSCG moieties can insert into the DSCG stacks that constitute the racemic tactoids. Overall, this presents a highly efficient pathway for chiral induction in an aqueous medium and thus for understanding the origins of biological homochirality in a suitable experimental system.

Frustrated 'run and tumble' of swimming Escherichia coli bacteria in nematic liquid crystals.

In many situations, bacteria move in complex environments, as soils, oceans or the human gut-track, where carrier fluids show complex structures associated with non-Newtonian rheology. Many fundamental questions concerning the ability to navigate in such environments remain unsolved. Recently, it has been shown that the kinetics of bacterial motion in structured fluids as liquid crystals (LCs) is constrained by the orientational molecular order (or director field) and that novel spatio-temporal patterns arise. A question unaddressed so far is how bacteria change swimming direction in such an environment. In this work, we study the swimming mechanism of a single bacterium, Esherichia coli, constrained to move along the director field of a lyotropic chromonic liquid crystal confined to a planar cell. Here, the spontaneous 'run and tumble' motion of the bacterium gets frustrated: the elasticity of the LC prevents flagella from unbundling. Interestingly, to change direction, bacteria execute a reversal motion along the director field, driven by the relocation of a single flagellum, a 'frustrated tumble'. We characterize this phenomenon in detail experimentally, exploiting exceptional spatial and temporal resolution of bacterial and flagellar dynamics, using a two colour Lagrangian tracking technique. We suggest a possible mechanism accounting for these observations.

The helical twisting power of chiral dopants in lyotropic chromonic liquid crystals

ABSTRACT Chiral dopants with different levels of lipophilicity were synthesised, and their helical twisting power (HTP) and thermal phase behaviour in mixtures with lyotropic chromonic liquid crystal (LCLC) were investigated. The experimental approach involved measurement of the positions of disclination lines in Θ-cells, where one surface is linearly rubbed, and the other is circularly rubbed. This technique allowed the use of minimal dopant concentrations. Experimental conditions were selected such that nematic temperature range of LCLC remained constant. We found that the twisting power of the used chiral dopants varies over nearly an order of magnitude between the molecules with positive and negative lipophilicity. All chiral molecules of hydrophobic nature investigated showed much higher effectiveness in twisting LCLC than hydrophilic ones, and in addition, the hydrophilic molecules had a much smaller effect on the transition temperatures of LCLC. The dependences were interpreted as a variation of the partition between the concentration of dopant dispersed in the host phase, between the columns and that adhering to the columnar stacks – with hydrophobic molecules better able to adhere, thus creating sources of chirality for the whole system.