Liquid Crystalline Solutions Research Articles

Nanotubes of a Different Kind: Stoichiometry and Geometry of the Orange II/γ-Cyclodextrin Complex in Water.

Orange II (O-II), a water-soluble ionic azo dye, aggregates and eventually forms needle-like crystals at concentrations greater than 0.15 M. However, when equimolar amounts of γ-cyclodextrin (γ-CD) are added to solutions containing O-II at 0.025 M or higher, the solution's appearance rapidly changes presenting a viscous, birefringent liquid, a lyotropic liquid crystalline solution. Birefringence is absent when viewing aqueous solutions of only O-II or γ-CD at concentrations greater than 0.03 M. Using ultraviolet-visible (UV-vis) and fluorescence spectroscopy, coupled with conductivity measurements, we postulate a structure for the basic "building block" of the self-assembly that eventually gives rise to a rodlike superstructure, leading to the formation of a lyotropic liquid crystalline phase.

Active Material‐Free Continuous Carbon Nanotube Fibers with Unprecedented Enhancement of Physicochemical Properties for Fiber‐Type Solid‐State Supercapacitors

AbstractFiber‐type solid‐state supercapacitors (FSSCs) are gaining traction as wearable energy storage devices, given their adaptability akin to traditional fibers. Carbon nanotube fibers (CNTFs) generated via a liquid crystalline (LC) wet‐spinning process demonstrate outstanding electrical conductivity, mechanical strength, and flexibility. However, their intrinsic “defect‐free” sp2 carbon surface restricts immediate FSSC application, limited by lower specific surface area and scant pseudocapacitive sites. This study develops LC‐spun CNTFs with inherent electrochemical activity, eliminating the need for post‐processing or additional active materials, a requirement typically essential in most previous research. This advancement arises from the wet‐spinning of functionalized CNTs from a LC solution with an exceptionally high concentration of 160 mg mL−1, facilitated by the manipulation of the LC phase transition range. The resultant CNTFs exhibit a refined internal structure, yielding an electrical conductivity of 1.9 MS m−1 and a mechanical strength of 0.93 GPa. Simultaneously, they demonstrate inherent electrical energy storage capabilities with a specific capacitance of 139.4 F g−1 and a volumetric capacitance of 192.4 F cm−3 at 0.5 A g−1. This innovation signifies a step forward in the potential for mass production without the burden of additional materials and steps.

Concentration Scaling on Linear Viscoelastic Properties of Cellular Suspensions and Effects of Equilibrium Phase Behavior.

Concentration scaling on linear viscoelastic properties of cellular suspensions has been studied by rheometric characterisation of Phormidium suspensions and human blood in a wide range of volume fraction under small amplitude oscillatory shear experiments. The rheometric characterisation results are analysed by the time-concentration superposition (TCS) principle and show a power law scaling of characteristic relaxation time, plateau modulus and the zero-shear viscosity over the concentration ranges studied. The results show that the concentration effect of Phormidium suspensions on their elasticity is much stronger than that of human blood due to its strong cellular interactions and a high aspect ratio. For human blood, no obvious phase transition could be observed over the range of hematocrits studied here and with respect to a high-frequency dynamic regime, only one concentration scaling exponent could be identified. For Phormidium suspensions with respect to a low-frequency dynamic regime, three concentration scaling exponents in the volume fraction Region I (0.36≤ϕ/ϕref≤0.46), Region II (0.59≤ϕ/ϕref≤2.89) and Region III (3.11≤ϕ/ϕref≤3.44) are identified. The image observation shows that the network formation of Phormidium suspensions occurs as the volume fraction is increased from Region I to Region II; the sol-gel transition takes place from Region II to Region III. In combination with analysis of other nanoscale suspensions and liquid crystalline polymer solutions reported in the literature, it is revealed that such a power law concentration scaling exponent depends on colloidal or molecular interactions mediated with solvent and is sensitive to the equilibrium phase behaviour of complex fluids. The TCS principle is an unambiguous tool to give a quantitative estimation.

Analysis of spinnable mesophase pitch in terms of lyotropic liquid crystalline solution

Analysis of spinnable mesophase pitch in terms of lyotropic liquid crystalline solution

Wet spinning imogolite nanotube fibres: an in situ process study.

Imogolite nanotubes (INTs) form transparent aqueous liquid-crystalline solutions, with strong birefringence and X-ray scattering power. They provide an ideal model system for studying the assembly of one-dimensional nanomaterials into fibres, as well as offering interesting properties in their own right. Here, in situ polarised optical microscopy is used to study the wet spinning of pure INTs into fibres, illustrating the influence of process variables during extrusion, coagulation, washing and drying on both structure and mechanical properties. Tapered spinnerets were shown to be significantly more effective than thin cylindrical channels for forming homogeneous fibres; a result related to simple capillary rheology by fitting a shear thinning flow model. The washing step has a strong influence of structure and properties, combining the removal of residual counter-ions and structural relaxation to produce a less aligned, denser and more networked structure; the timescales and scaling behavior of the processes are compared quantitatively. Both strength and stiffness are higher for INT fibres with a higher packing fraction and lower degree of alignment, indicating the importance of forming a rigid jammed network to transfer stress through these porous, rigid rod assemblies. The electrostatically-stabilised, rigid rod INT solutions were successfully cross-linked using multivalent anions, providing robust gels, potentially useful in other contexts.

Solid-liquid equilibrium of free form of oil contaminants (3-MCPD and glycidol) in lipidic systems

Esters of 3-monochloropropane-1,2-diol (3-MCPD) and glycidol are reported vegetable fats and oils contaminants formed during processing. During digestion, esterified forms are hydrolyzed making the free forms, with high toxicity to human health, possibly available in the digestive system, which could depend, among other factors, on the phase condition stablished in the gastrointestinal tract between contaminants and lipids. Therefore, this work was aimed at evaluating the solid–liquid equilibrium (SLE) of binary and pseudobinary mixtures of fatty acids (palmitic, oleic and stearic), triacylglycerols (tripalmitin, triolein and tristearin) and a partial acylglycerols, with 3-MCPD and glycidol, by differential scanning calorimetry (DSC) and thermodynamic modeling with Margules 2 and 3 suffixes, UNIFAC and ideal models. Melting properties of the contaminants were determined by DSC thermograms, with microstructure micrographs and compared to some predictive group contribution models (GC). 14 complete SLE phase diagrams could be determined. Results showed that the lipid compounds had high affinity with the free contaminants with probably the formation of liquid crystalline structures and/or solid solutions. The Margules 3 suffixes model showed the best fit with the lowest average relative deviations, no higher than 1%, although the parameters probably incorporated the non-ideality promoted by the crystalline phase behavior. The formation of mesophases and/or solid solutions with very high melting temperature probably means a difficulty of separating the contaminants from the lipid matrix in which, on the other hand, could avoid separation process or affect (probably decreasing) their absorption during digestion.

Design and Analysis of a Mandrel Process to Control the Properties of Poly(p-Phenylene Terephthalamide) Films

Abstract Kinematic and rheological considerations have been used to design and analyze the processing steps for obtaining biaxial chain orientation in poly(p-phenylene terephthalamide) (PPTA) films. A semi-quantitative approach to the mandrel design allows one to predict the type and degree of molecular orientation obtained. For the case of PPTA dissolved in H2SO4, the basic steps are extrusion of the liquid crystalline solution through an annular die followed by expansion and elongational flow over a mandrel. The mandrels used include conical, hyperbolic and ogival shapes. Molecular orientation as well as mechanical properties were found to be dependent on mandrel shape and presence. Wide angle x-ray diffraction (WAXS) techniques using White-Spruiell orientation factors and pole figures were used to characterize the films. Mechanical properties as well as the above techniques indicate a high degree of biaxial orientation can be obtained with a bias in certain film directions depending on the mandrel used. Tensile strength and Young's modulus values were found to be on the order of 30 000 psi and one million psi respectively. They also can be equally distributed in the film plane depending on mandrel shape. White-Spruiell orientation factors were as high as 0.49 and 0.5 for f 1 B a n d f 2 B $f_{1}^{B}\text{ }and\text{ }f_{2}^{B}$ respectively. Scanning electron microscopy was used to observe the film superstructure as a function or processing conditions. All films exhibited a skin-core structure. Uniaxially drawn films are fibillar while the biaxial films appear to be more homogeneous.

Chlorin e6 13(N)-methylamide-15,17-dimethyl ester and its nickel complex as the inducers of chiral nematic liquid crystals

To search for new effective inducers of helical liquid-crystalline phases, chlorin e6 13 (N)-methylamide-15,17-dimethyl ester (MADMECl) and its nickel complex (Ni-MADMECl) were studied. An increase in the optical activity of the chlorin e6 derivative upon complexation with nickel, associated with a distortion of the macrocycle structure, was established by circular dichroism spectroscopy and quantum chemistry. The introduction of a macrocyclic complex into binary LC mixtures based on cyanobiphenyls (CB-2) and Schiff bases (SB-2), as well as the macrocyclic ligand MADMECl in CB-2, was shown to induce the formation of helical LC phases with high helical twisting power (maximum HTP = 409 μm−1 for the mixture CB-2 + Ni-MADMECl). The HTP decreases with an increase in the additive concentration. The assessment of the dopant influence on the LC thermal stability was carried out. The temperature dependences of the permittivity components of the studied liquid-crystalline solutions were obtained at different dopant concentrations. The relationship between the dielectric anisotropy and the helical pitch is established due to the 3D compensation of molecular dipoles. Quantum-chemical simulation of dopant-LC solvates was performed. The influence of the energy of intermolecular interaction on the efficiency of nematic phase twisting was ascertained. The contribution of supramolecular chirality to the process of chiral induction was detected.

Rheological Properties of Liquid Crystalline Solutions of Cellulose Derivatives

Rheological Properties of Liquid Crystalline Solutions of Cellulose Derivatives

Electro-optical properties of a liquid crystalline colloidal solution of rod shaped V2O5 nanoparticles and carbon nanotubes in an alternating current electric field

ABSTRACT We study the liquid crystalline phase behaviour of the two-component aqueous colloidal suspensions of multiwalled carbon nanotubes (MWCNTs) and rod-like vanadium pentoxide (V2O5) nanoparticles. The phase diagram features a stable nematic phase in a wide range of concentration of solid components. The oriented nematic phase of the two-component suspension was exposed to the action of alternating current electric field. A variation in MWCNTs concentration within 0.01–0.51 wt.% demonstrates a significant increase in the optical response of the system to the applied electric field.

Interfacial self-assembly of polysaccharide rods and platelets bridging over capillary lengths

HypothesisGeneration of long-range ordering of colloidal particles through anisotropic interactions is of growing interest in material designing. At submicron-scale, routine works use synthetic spheres or rods but the knowledge pertaining to assembly of binary combination of particles is severely restricted. Improved understanding of the fundamental aspects that drive self-assembly, can lead to robust strategies for fabrication of topographically oriented films. ExperimentThe fluidical geometry of a liquid crystalline (LC) solution of polysaccharide consisting of micron-sized rod and platelet units was explored. The solutions, characterized for their rheological behavior, were evaporated from a rectangular cavity. The assembly and orientation of the units was monitored by polarizing microscopy and the interparticle capillary forces approximated mathematically. FindingsThe units deposited into an uninterrupted membrane upon interfacial evaporation, forming a bridge along the 8 mm gap, linking the substrates. The membrane, composed of a lamellar structure, was uniaxially oriented along the direction of the gap. The rheological estimations corroborated an extremely high value of viscosity with the presence of crosslinking junctions in this solution when compared to a solution with only rod units, capable of bridging a maximum of 1 mm. It has been demonstrated for the very first time that the presence of platelet-units contributes lateral capillary interactions and assist rod-units towards a wider, self-assembled structure.

Treating anisotropic artefacts in circular dichroism spectroscopy enables investigation of lyotropic liquid crystalline polyaspartate solutions.

Circular dichroism (CD) spectroscopy is commonly used for investigation of the secondary structure of biomolecular compounds as well as polymers in isotropic solution. In anisotropic solution, the usage of the apparent CD is prone to misinterpretations due to artefacts from contributions of e.g. linear dichroism (LD). Herein, a method for the complete cancelation of anisotropic artefacts in the apparent CD is developed and its validity proven. The approach is further used for investigation of the conformation and the lyotropic liquid crystalline (LLC) structure of a copolyaspartate. For this system, a temperature-dependent change of the polymer's helical conformation (helix reversal) is known. Furthermore, a rotation of the aligned polymer helices inside a magnetic field (helix realignment) is independently present, occurring at a lower temperature compared to the helix reversal. In the current study, the helix reversal is confirmed and found to be accompanied by a change of the LLC structure. A cholesteric structure is detected and revealed to change its sense (cholesteric reversal) at the temperature at which the helix realigns in the magnetic field. The determination of the cholesteric sense is enabled by measuring the induced CD of an achiral dye, dissolved in the anisotropic polymer solution. Investigation of the anisotropic polymer solution is, thus, only made possible by cancellation of the aforementioned anisotropic artefacts. This allows the observation of changes of the liquid crystal structure from right-handed cholesteric, through left-handed cholesteric, to nematic with increasing temperature.

Enhanced ordering in length-polydisperse carbon nanotube solutions at high concentrations as revealed by small angle X-ray scattering.

Carbon nanotubes (CNTs) are stiff, all-carbon macromolecules with diameters as small as one nanometer and few microns long. Solutions of CNTs in chlorosulfonic acid (CSA) follow the phase behavior of rigid rod polymers interacting via a repulsive potential and display a liquid crystalline phase at sufficiently high concentration. Here, we show that small-angle X-ray scattering and polarized light microscopy data can be combined to characterize quantitatively the morphology of liquid crystalline phases formed in CNT solutions at concentrations from 3 to 6.5% by volume. We find that upon increasing their concentration, CNTs self-assemble into a liquid crystalline phase with a pleated texture and with a large inter-particle spacing that could be indicative of a transition to higher-order liquid crystalline phases. We explain how thermal undulations of CNTs can enhance their electrostatic repulsion and increase their effective diameter by an order of magnitude. By calculating the critical concentration, where the mean amplitude of undulation of an unconstrained rod becomes comparable to the rod spacing, we find that thermal undulations start to affect steric forces at concentrations as low as the isotropic cloud point in CNT solutions.

Supramolecular Association and Nanostructure Formation of Liquid Crystals and Polymers for New Functional Materials

AbstractWe here describe our various concepts and achievements for material science, which have been introduced through liquid-crystalline (LC) and polymer chemistry. They have resulted in the development of new classes of functional organic, polymer, and hybrid materials. Supramolecular LC complexes and polymers with well-defined structures were found to be built through complimentary hydrogen bonding between carboxylic acid and pyridine. Since then, a variety of intermolecular interactions such as hydrogen bonding, ionic interactions, ion-dipolar interactions, and halogen bonding were used for the formation of supramolecular liquid crystal organic materials and polymers. The nanosegregation in molecular assemblies in liquid crystals leads to the various 1D, 2D and 3D self-assembled nanostructures. These strategy and material designs lead to the development of new dynamically functional materials, which exhibit stimuli-responsive properties, photoluminescence, transport of charge, ions, and molecules, electro-optic properties, and templates. We also show new hybrid liquid crystals, biomineral-inspired nanorod and nanodisk liquid crystals. These nanomaterials form colloidal LC solutions, which exhibit stimuli-responsive properties.

Irreversible Shear-Activated Gelation of a Liquid Crystalline Polyelectrolyte.

We report irreversible, shear-activated gelation in liquid crystalline solutions of a rigid polyelectrolyte that forms rodlike assemblies (rods) in salt-free solution. At rest, the liquid crystalline solutions are kinetically stable against gelation and exhibit low viscosities. Under steady shear at, or above, a critical shear rate, a physically cross-linked, nematic gel network forms due to linear growth and branching of the rods. Above a critical shear rate, the time scale of gelation can be tuned from hours to nearly instantaneously by varying the shear rate and solution concentration. The shear-activated gels are distinct in their structure and rheological properties from thermoreversible gels. At a fixed concentration, the induction time prior togelation decreases exponentially with the shear rate. This result indicates that shear-activated thermalization of the electrostatically stabilized rods overcomes the energy barrier for rod-rod contact, enabling rod fusion and subsequent irreversible network formation.

Strong graphene oxide nanocomposites from aqueous hybrid liquid crystals

Combining polymers with small amounts of stiff carbon-based nanofillers such as graphene or graphene oxide is expected to yield low-density nanocomposites with exceptional mechanical properties. However, such nanocomposites have remained elusive because of incompatibilities between fillers and polymers that are further compounded by processing difficulties. Here we report a water-based process to obtain highly reinforced nanocomposite films by simple mixing of two liquid crystalline solutions: a colloidal nematic phase comprised of graphene oxide platelets and a nematic phase formed by a rod-like high-performance aramid. Upon drying the resulting hybrid biaxial nematic phase, we obtain robust, structural nanocomposites reinforced with graphene oxide.

ZnO decorated flexible and strong graphene fibers for sensing NO2 and H2S at room temperature

Here we present toxic gas fiber-based sensor, operating at room temperature, which is important in wearable electronics for monitoring the environment and human health. Continuous strong and flexible graphene oxide (GO) fibers, with aligned GO sheets are synthesized by transforming a prealigned liquid crystalline GO solution using a wet spinning assembly. GO fibers are chemically reduced (rGO) for imparting resistance-based gas sensing. ZnO decorated rGO fibers (ZrGO) are synthesized by hydrothermal-assisted chemical reduction of GO fibers. ZnO nanoparticles and flowers, grown on ZrGO fibers, provided more surface area for adsorption of gas molecules compared to rGO fibers. Furthermore, ZrGO fibers provided more catalytic sites for gas interactions to enhance the sensing performance. The fiber-sensor can detect minimum levels of 1.5 and 8 ppm of NO2 and H2S gas, respectively. Interestingly, the sensing performance of ZrGO fiber-sensor is increased by 8 and 24-fold for NO2 and H2S, respectively, compared to rGO. The fiber-sensor shows fast recovery for H2S compared to NO2 gas. This work opens a new way for the application of robust, lightweight, cheap, and room temperature chemical sensors, that can detect hazardous gases.

Playing the blues, the greens and the reds with cellulose-based structural colours.

Structural vivid colours can arise from the interference of light reflected from structures exhibiting periodicity on scales in the range of visible wavelengths. This effect is observed with light reflected from cell-walls of some plants and exoskeletons of certain insects. Sometimes the colour sequence observed for these structures consists of nearly circular concentric rings that vary in colour from Red, Orange, Yellow, Green, Cyan to Blue, from the periphery to the centre, similarly to the colour scheme sequence observed for the rainbow (ROYGB). The sequence of colours has been found for solid films obtained from droplets of aqueous cellulose nanocrystals (CNCs) suspensions and attributed to a "coffee ring" effect. In this work, coloured lyotropic solutions and solid films obtained from a cellulose derivative in the presence of trifluoroacetic acid (TFA), which acts as a "reactive solvent", are revisited. The systems were investigated with spectroscopy, using circularly and linearly polarised light, coupled with a polarised optical microscope (POM) and scanning electron microscopy (SEM). The lyotropic cholesteric liquid crystalline solutions were confined in capillaries to simplify 1D molecular diffusion along the capillary where an unexpected sequence of the structural colours was observed. The development and reappearance of the sequence of vivid colours seem consistent with the reaction-diffusion of the "reactive solvent" in the presence of the cellulosic chains. The strong TFA acts as an auto-catalyst for the chemical reaction between TFA and the hydroxyl groups, existing along the cellulosic chain, and diffuses to the top and bottom along the capillaries, carrying dissolved cellulosic chains. Uncovering the precise mechanism of colour sequence and evolution over time in cellulosic lyotropic solutions has important implications for future optical/sensors applications and for the understanding of the development of cellulose-based structures in nature.

Observation of transition cascades in sheared liquid crystalline polymers.

We report on the shear rheology of liquid crystalline solutions composed of charged, rodlike polymers that form supramolecular assemblies dispersed in water. Under steady shear, we observe shear thickening behavior, followed by a hesitation in the viscosity accompanied by an extremely narrow range of negative first normal stress difference. The Peclet number (Pe, shear rate normalized by rod rotational diffusivity) for the onset of shear thickening is in agreement with previous, high-resolution numerical simulations of the Doi-Edwards-Hess kinetic theory. We interrogate these dynamic responses through shear step-down experiments, revealing a complex evolution of transient responses. Detailed analysis of the stress transients provides compelling evidence that the principal axis of the rod orientational distribution, the nematic director, undergoes a cascade of transitions and coexistence of periodic states known as kayaking, tumbling, and wagging, before transitioning to steady flow alignment above a critical shear rate.

Structural Understanding, Photoswitchability, and Supergelation of a New Class of Four Ring-Based Bent-Shaped Liquid Crystal.

Herein, we report a new type of azobenzene-based unsymmetrical bent-core molecules exhibiting photoswitchability in the liquid crystalline state, solid state, and solution state and in mixture upon UV irradiation and intense visible light. The compounds exhibited solid-state photochromism upon exposure to UV light, whereas in liquid crystalline state, reversible phase transitions were observed via both UV irradiation and intense visible light exposure. Crystal structure analysis reveals the basic structural understanding such as nonplanar bent molecular shape, antiparallel arrangement of the polar bent molecules, intra- and intermolecular hydrogen bonding, and different π-π interactions and interdigitation of long alkyl chains. The compounds are also found to act as supergelator toward various organic solvents. Hence, this is an excellent example of such potential bent-shaped liquid crystals that promise an immense perspective for device applications such as optical storage, molecular switches, etc.