Liquid Crystalline Dispersions Research Articles

An inorganic liquid crystalline dispersion with 2D ferroelectric moieties.

Electro-optical effect-based liquid crystal devices have been extensively used in optical modulation techniques, in which the Kerr coefficient reflects the sensitivity of the liquid crystals and determines the strength of the device's operational electric field. The Peterlin-Stuart theory and the O'Konski model jointly indicate that a giant Kerr coefficient could be obtained in a material with both a large geometrical anisotropy and an intrinsic polarization, but such a material is not yet reported. Here we reveal a ferroelectric effect in a monolayer two-dimensional mineral vermiculite. A large geometrical anisotropy factor and a large inherent electric dipole together raise the record value of Kerr coefficient by an order of magnitude, till 3.0×10-4mV-2. This finding enables an ultra-low operational electric field of 102-104Vm-1 and the fabrication of electro-optical devices with an inch-level electrode separation, which has not previously been practical. Because of its high ultraviolet stability (decay <1% under ultraviolet exposure for 1000 hours), large-scale production, and energy efficiency, prototypical displayable billboards have been fabricated for outdoor interactive scenes. This work provides new insights for both liquid crystal optics and two-dimensional ferroelectrics.

Preparing a liquid crystalline dispersion of carbon nanotubes with high aspect ratio.

We successfully prepared a surfactant-assisted carbon nanotube (CNT) liquid crystal (LC) dispersion with double-walled CNTs (DWCNTs) having a high aspect ratio (≈1378). Compared to dispersions of single-walled CNTs (SWCNTs) with lower aspect ratio, the transition concentrations from isotropic phase to biphasic state, and from biphasic state to nematic phase are lowered, which is consistent with the predictions of the Onsager theory. An aligned DWCNT film was prepared from the DWCNT dispersion by a simple bar-coating method. Regardless of the higher aspect ratio, the order parameter obtained from the film is comparable to that from SWCNTs with lower aspect ratios. This finding implies that precise control of the film formation process, including a proper selection of substrate and deposition/drying steps, is crucial to maximize the CNT-LC utilization.

Recent advances and opportunities in MXene‐based liquid crystals

AbstractThe recent progress on the liquid crystalline (LC) dispersion of two‐dimensional (2D) transition metal carbides (MXenes) has propelled this unique nanomaterial into a realm of high‐performance architectures, such as films and fibers. Additionally, compared to architectures made from typical non‐LC dispersions, those derived from LC MXene possess tunable ion transport routes and enhanced conductivity and physical properties, demonstrating great potential for a wide range of applications, such as electronic displays, smart glasses, and thermal camouflage devices. This review provides an overview of the progress achieved in the production and processing of LC MXenes, including critical discussions on satisfying the required conditions for LC formation. It also highlights how acquiring LC MXenes has broadened the current solution‐based manufacturing paradigm of MXene‐based architectures, resulting in unprecedented performances in their conventional applications (e.g., energy storage and strain sensing) and in their emerging uses (e.g., tribology). Opportunities for innovation and foreseen challenges are also discussed, offering future research directions on how to further benefit from the exciting potential of LC MXenes with the aim of promoting their widespread use in designing and manufacturing advanced materials and applications.image

Optical Polymorphism of Liquid-Crystalline Dispersions of DNA at High Concentrations of Crowding Polymer.

Optically active liquid-crystalline dispersions (LCD) of nucleic acids, obtained by polymer- and salt-induced (psi-) condensation, e.g., by mixing of aqueous saline solutions of low molecular weight DNA (≤106 Da) and polyethylene glycol (PEG), possess an outstanding circular dichroism (CD) signal (so-called psi-CD) and are of interest for sensor applications. Typically, such CD signals are observed in PEG content from ≈12.5% to ≈22%. However, in the literature, there are very conflicting data on the existence of psi-CD in DNA LCDs at a higher content of crowding polymer up to 30-40%. In the present work, we demonstrate that, in the range of PEG content in the system above ≈24%, optically polymorphic LCDs can be formed, characterized by both negative and positive psi-CD signals, as well as by ones rather slightly differing from the spectrum of isotropic DNA solution. Such a change in the CD signal is determined by the concentration of the stock solution of PEG used for the preparation of LCDs. We assume that various saturation of polymer chains with water molecules may affect the amount of active water, which in turn leads to a change in the hydration of DNA molecules and their transition from B-form to Z-form.

Highly efficient oxidation of single-walled carbon nanotubes in liquid crystalline phase and dispersion for applications in Li-ion batteries

Single-walled carbon nanotubes (SWCNTs), which have high electrical conductivity, are promising candidates for enhancing the energy storage capability of lithium-ion batteries (LIBs). However, their usage in energy storage devices is limited due to the large bundle size and difficulties in dispersion. Here, we implement the debundling and mild oxidation of SWCNTs in the liquid crystalline phase paste (2 wt% solid content) with strong acid and co-intercalant (NaNO3). The thermal treatment successfully introduced carboxylic acid groups without requiring other oxidizing agents. The pretreated SWCNTs were dispersed in organic solvents such as N-methyl pyrrolidone (NMP) without dispersant molecules and were utilized as conductive additives for LIBs. Raman spectroscopy analysis showed that the D/G ratio of the SWCNT film changed from 0.012 to 0.023, implying that the oxidation method proposed herein is less defective and efficient. The filtrated 15 μm film of the SWCNTs exhibited a high electrical conductivity of 2384 S/cm. SWCNT dispersion in NMP was utilized to fabricate LIB cathode electrodes. Compared to the carbon black-applied electrodes, the SWCNT-applied LiNi0.8Co0.1Mn0.1O2 (NCM811) electrodes exhibited enhanced dispersity of conductive additive/binder networks, leading to improved electrode integrity. The capacity retention after 100 cycles for cells with SWCNTs was approximately 23.3 % better than that of the cells without SWCNTs.

A Principal Approach to the Detection of Radiation-Induced DNA Damage by Circular Dichroism Spectroscopy and Its Dosimetric Application

Using cholesteric liquid-crystalline dispersion (CLCD) of DNA, we demonstrate that the molecularly organized systems may be used both for qualitative assessment of the degree of radiation-induced DNA damage, as well as for detection of radiation doses in a very wide range. The doses up to 500 Gy do not cause any significant changes in optical signals of DNA in solution. However, when irradiated molecules are used to prepare the CLCD by addition of crowding polymer, a clear correlation of its optical signals with an absorbed dose is observed. For example, at a dose of 500 Gy, a maximum drop in the circular dichroism (CD) signal for DNA solution and for CLCD formed from preliminary irradiated molecules is ≈20% and ≈700%, respectively. This approach can also be used to expand the dosimetric capabilities of DNA CLCD. Compared to the case of irradiation of ready-made DNA CLCD, formation of the dispersed system from irradiated DNA allows to increase its sensitivity by more than 2 orders of magnitude. A similar decrease in the CD signal (≈1.45-fold) is observed in these systems at the doses of 100 kGy and 200 Gy, respectively. This principal approach seems to be relevant for other biomolecules and molecularly organized systems.

Förster resonance energy transfer from Hoechst 33258 to SYBR Green I in cholesteric liquid-crystalline DNA

In the present work Förster resonance energy transfer (FRET) between DNA-specific fluorescent dyes Hoechst 33258 (Ht58; donor) and SYBR Green I (SG; acceptor) is compared in isotropic DNA solution and in its cholesteric liquid-crystalline dispersion (DNA CLCD). At a fixed donor concentration of 3.57 × 10−6 М in the spatially ordered system, FRET starts at lower acceptor concentration than in the isotropic system and at the SG concentration below 1.05 × 10−7 M, its efficiency in DNA CLCD is up to ≈4-fold higher than in DNA solution (3D-FRET vs. 1D-FRET). However, the maximum FRET efficiency is higher in isotropic solution (≈70% vs. ≈50%, respectively) apparently due to the absence of steric restrictions on intermolecular interactions imposed by the dense packaging of the DNA molecules. In isotropic DNA solution FRET from Ht58 to SG is accompanied by the displacement of Ht58 from the minor-groove complex as the SG concentration increased, while the displacement of Ht58 in DNA CLCD seems to be limited. Using FRET between Ht58 and SG, the formation of DNA CLCD particles via stopped-flow method was investigated and for the first time the subsecond stage of the DNA CLCD particle formation, generation of “precholesteric” optically inactive nuclei, was demonstrated.

Liquid Crystalline Behaviors of Single-Walled Carbon Nanotubes in an Aqueous Sodium Cholate Dispersion.

Controlling the alignment of single-walled carbon nanotubes (SWCNTs) on the macroscopic scale is critical for practical applications because SWCNTs are extremely anisotropic materials. One efficient technique is to create an effective SWCNT dispersion, which shows a liquid crystal (LC) phase. A strong acid treatment can realize SWCNT liquid crystalline dispersions. However, strong acids pose a substantial safety risk, which renders the process unfit for mass production. Herein, an isolated SWCNT dispersion displaying an LC behavior is prepared using sodium cholate without an acid treatment, and its phase transition behaviors are systematically investigated across the isotropic to biphasic to nematic phases. As the SWCNT concentration increases, the dispersion undergoes an isotropic-to-nematic phase transition in which the spindle-shaped LC droplets, or the so-called tactoids, and the Schlieren textures can be observed in the intermediate biphasic state and the nematic phase, respectively. The arrangements of SWCNTs in the tactoids and the Schlieren structures are directly investigated by polarized optical microscopy. The clear LC behaviors of the CNT dispersion suggest that the CNT orientations can be controlled by the normal surfactant-assisted method, which is a crucial advantage for the liquid-phase processing of CNT fibers and films.

Photonic liquid crystals of graphene oxide for fast membrane nanofiltration

The photonic liquid crystalline (LC) dispersion of graphene oxide (GO) is prepared using centrifugation-induced size-fractionization. Under gravity, a series of successive centrifugations enable large GO sheets to sediment and fractionize into a narrowed size distribution. The resulting large GO sheets display large-area monodomain structures with uniform orientation, forming a photonic LC phase. The single lyotropic LC phase forms at the concentration > 0.34 wt% and structural coloring occurs at the concentration > 0.59 wt%. The structural color with different wavelength is tuned with various concentrations (0.59–0.92 wt%). GO membranes are supported on porous poly(ether sulphone) membranes from photonic LC dispersions by a vacuum-spin method. The photonic GO membrane demonstrates dramatic enhancement of water permeance (169.3 Lm −2 hr −1 bar −1 ), which is 12 times faster than the control GO membrane (13.2 Lm −2 hr −1 bar −1 ). The ion rejection of the photonic GO membrane (45–60%) is also significantly improved, as compared to the control GO membrane (30–48%). Organic dye rejection testing shows that the photonic GO membrane remains as high molecular rejection (> 90%) as the control GO membrane. This work may provide a new way to fabricate ordered GO membranes for fast nanofiltration.

Cholesteric liquid-crystalline DNA – a new type of chemical detector of ionizing radiation

ABSTRACT Liquid crystals (LCs) can be promising for detection of ionising radiation (IR). However, there is little information about their interaction with IR and there are no systemic studies of the dosimetric application of LCs. In this communication, we show for the first time the capabilities of a new type of radiation detector – cholesteric liquid-crystalline dispersion (CLCD) of DNA obtained using polyethylene glycol (PEG) and salt indued condensation. Irradiation of the DNA CLCD samples with 0–100 kGy of 7.6 MeV bremsstrahlung led to significant change in their circular dichroism (CD): ≈5% and ≈12% increase in the signal was observed at 10 and 20 kGy, while in the range of 20–90 kGy the CD signal decreased linearly. Thus, detectors based on DNA CLCD could be of interest for such application of IR as material modification or radiation sterilisation. At the same time irradiation can help to stabilise dispersion particles and can be used to prevent their sedimentation. Unirradiated samples degraded within 24 h after preparation, while the irradiated ones were able to maintain the intensity of CD signal for more than 168 h.Schematic representation of the dual effect of radiation exposure the DNA CLCD.

Highly Efficient Oxidation of Single-Walled Carbon Nanotubes in Liquid Crystalline Phase and Dispersion for Applications in Li-Ion Batteries

Highly Efficient Oxidation of Single-Walled Carbon Nanotubes in Liquid Crystalline Phase and Dispersion for Applications in Li-Ion Batteries

Observations of three "re-entrant" twisted structures in double-stranded DNA dispersion particles.

In this work we report on observations of new twisted (cholesteric-like) structures in liquid-crystalline dispersion particles with a hexagonal packing of double-stranded (ds) DNA molecules. Heating up to 80°C of the DNA dispersion formed in a aqueous-salt solution with a high osmotic pressure (concentration) of poly(ethylene glycol) induces the formation of a new, optically active, spirally twisted structure of these molecules ("re-entrant" cholesteric structure (rest-A structure)). Cooling of this dispersion up to 22°C is accompanied by the formation of an additional "re-entrant" cholesteric structure (rest-B). Modification of particles of the ds DNA dispersion (with rest-B structure) by replacing Na+ cations by multi-charged Gd3+ cations results in the third " re-entrant" structure (rest-C) despite a high density packing of ds nucleic acid molecules.

Lyotropic liquid crystalline phases of anisotropic nanoparticles of organic-inorganic metal halide perovskites: photoluminescence from self-assembled ordered microstructures of semiconductors.

A simple method (which could be completed within 60 minutes at 298 K) was developed to transform layered organic-inorganic metal halide perovskites into colloidal lyotropic liquid crystalline dispersions with microscopic structural orderliness as well as semiconducting properties and photoluminescence. Experimentally, hexagonal-shaped mesogenic nanoplatelets of two-dimensional lead iodide perovskites (R-NH3)2PbI4 were synthesized by antisolvent-induced rapid microcrystallization and stabilized by surfactants, and self-assembled into discotic-nematic phases with optical anisotropy and greenish-blue fluorescence. Combining the stimuli-responsive, light-interactive, and reconfigurable ordered structures of liquid crystals with the adjustable semiconductivity of hybrid perovskites, these photoluminescent soft anisotropic materials may be used for polarized light emission or detection.

Comparison of quenching efficacy of SYBR Green I and PicoGreen fluorescence by ultrasmall gold nanoparticles in isotropic and liquid-crystalline DNA systems

Gold nanoparticles (GNPs) are promising for sensors based on fluorescence quenching. Conjunction of GNPs to liquid crystalline (LC) matrix may improve their quenching properties. In the present work the quenching of SYBR Green I (SG) and PicoGreen (PG) fluorescence by negatively charged 2.5 nm GNPs was investigated in an isotropic DNA solution and in its cholesteric liquid crystalline dispersion (DNA CLCD). These dyes have similar chromophore structures and spectral properties but different charges: +2 (SG) and +3 (PG). The most efficient static fluorescence quenching was observed at the lowest concentration of dyes: in the DNA CLCD for SG (KSV = 7.4 × 107 M−1) and in the isotropic DNA solution for PG (KSV = 1.54 × 108 M−1). Since in the DNA solution quenching was due to the formation of a non-fluorescent complex with GNPs, the quenching was up to ~70-fold more efficient for PG than for SG. In the DNA CLCD the quenching efficacy of SG fluorescence increased up to ~15-fold because of the energy transfer. At the same time, due to steric hindrance for the interaction of PG with GNPs in the DNA CLCD caused by tight packaging of DNA molecules, the fluorescence quenching efficacy was ~5-fold higher in the isotropic solution.

Множественность "возвратных" холестерических структур в жидкокристаллических дисперсиях ДНК

Множественность "возвратных" холестерических структур в жидкокристаллических дисперсиях ДНК

Lightweight Ultra-High-Barrier Liners for Helium and Hydrogen.

Upcoming efficient air-borne wind energy concepts and communication technologies applying lighter-than-air platforms require high-performance barrier coatings, which concomitantly and nonselectively block permeation not only of helium but also of ozone and water vapor. Similarly, with the emergence of green hydrogen economy, lightweight barrier materials for storage and transport of this highly diffusive gas are very much sought-after, particularly in aviation technology. Here the fabrication of ultraperformance nanocomposite barrier liners by spray coating lamellar liquid crystalline dispersions of high aspect ratio (∼20 000) silicate nanosheets mixed with poly(vinyl alcohol) on a PET substrate foil is presented. Lightweight nanocomposite liners with 50 wt % filler content are obtained showing helium and hydrogen permeabilities as low as 0.8 and 0.6 cm3 μm m-2 day-1 atm-1, respectively. This exhibits an improvement up to a factor of 4 × 103 as compared to high-barrier polymers such as ethylene vinyl alcohol copolymers. Furthermore, ozone resistance, illustrated by oxygen permeability measurements at elevated relative humidity (75% r.h.), and water vapor resistance are demonstrated. Moreover, the technically benign processing by spray coating will render this barrier technology easily transferable to real lighter-than-air technologies or irregular- and concave-shaped hydrogen tanks.

Fluorescence superquenching of SYBR Green I in crowded DNA by gold nanoparticles

Gold nanoparticles (GNPs) are known to efficiently quench fluorescence with high constants (107-1011 M−1). Quenching efficiency is determined by GNPs parameters, the properties of dye complex with biomolecular substrate may also affect this efficiency. In the present work quenching of SYBR Green I fluorescence by 2.5 nm GNPs was investigated in an isotropic DNA solution and on cholesteric (DNA CLCD) and hexagonal (DNA HLCD) liquid crystalline dispersion templates obtained with polymer and salt-induced condensation. Superquenching of SYBR Green I fluorescence was observed in all investigated models. The quenching efficiency increased as the DNA molecules were spatially ordered: the greatest quenching was observed for DNA HLCD where DNA molecules are packed most densely. In the condensed DNA systems, unlike DNA solution, the mechanism of quenching was not only the formation of a nonfluorescent complex, but also energy transfer between dye molecules and GNPs. The Stern-Volmer and Perrin models were insufficient for description of quenching processes. The Perrin equation was in an agreement with experiment only for DNA in solution. The model of microphase separation most adequately described the SYBR Green I fluorescence quenching by GNPs in DNA solution as well as in the molecularly organized DNA CLCD and DNA HLCD.

Effect of pyrolyzed catecholamine polymers for concurrent enhancements of electrical conductivity and mechanical strength of graphene-based fibers

Graphene fibers are regarded as a novel platform material for flexible electronic applications based on their superior electrical conductivity, mechanical properties and potential for mass production. However, properties of graphene fibers are still far from commercial level and considerable effort has been made recently to improve these characteristics. In this paper, we drastically enhanced both the mechanical and electrical properties of graphene-based fibers by converting infiltrated polydopamine (PDA) into N-doped graphitic layers. Graphene-based fibers were fabricated from a liquid crystalline graphene oxide dispersion, and PDA was introduced into the fibers. After pyrolysis, the mechanical properties, i.e., the tensile strength and Young's modulus, of the composite graphene-based fibers exhibited 3.56- and 3.95-fold increases, respectively, compared with those of pristine graphene fibers. Furthermore, the electrical conductivity also dramatically increased to 7.3 × 104 S/m, which is almost 10 times that of pristine graphene fibers. These results show the achievement of advantages superior to those in previously reported studies based on polymer-grafted graphene composite fibers. This hybridized composite fabrication process provides a new way of reinforcing graphene fibers and contributes to expanding the application of graphene-based fibers in flexible electronic devices.

Cellular uptake of self-assembled phytantriol-based hexosomes is independent of major endocytic machineries

Despite increasing interests in non-lamellar liquid crystalline dispersions, such as hexosomes, for drug delivery, little is known about their interactions with cells and mechanism of cell entry. Here we examine the cellular uptake of hexosomes based on phytantriol and mannide monooleate by HeLa cells using live cell microscopy in comparison to conventional liposomes. To investigate the importance of specific endocytosis pathways upon particle internalization, we silenced regulatory proteins of major endocytosis pathways using short interfering RNA. While endocytosis plays a significant role in liposome internalization, hexosomes are not taken up via endocytosis but through a mechanism that is dependent on cell membrane tension. Biophysical studies using biomembrane models highlighted that hexosomes have a high affinity for membranes and an ability to disrupt lipid layers. Our data suggest that direct biomechanical interactions of hexosomes with membrane lipids play a crucial role and that the unique morphology of hexosomes is vital for their membrane activity. Based on these results, we propose a mechanism, where hexosomes destabilize the bilayer, allowing them to “phase through” the membrane. Understanding parameters that influence the uptake of hexosomes is critical to establish them as carrier systems that can potentially deliver therapeutics efficiently to intracellular sites of action.

Liquid-Crystalline Dispersions of Double-Stranded DNA

In this review, we compare the circular dichroism (CD) spectra of liquid-crystalline dispersion (LCD) particles formed in PEG-containing aqueous-salt solutions with the purpose of determining the packing of ds DNA molecules in these particles. Depending on the osmotic pressure of the solution, the phase exclusion of ds DNA molecules at room temperature results in the formation of LCD particles with the cholesteric or the hexagonal packing of molecules. The heating of dispersion particles with the hexagonal packing of the ds DNA molecules results in a new phase transition, accompanied by an appearance of a new optically active phase of ds DNA molecules. Our results are rationalized by way of a concept of orientationally ordered “quasinematic” layers formed by ds DNA molecules, with a parallel alignment in the hexagonal structure. These layers can adopt a twisted configuration with a temperature increase; and as a result of this process, a new, helicoidal structure of dispersion particle is formed (termed as the “re-entrant” cholesteric phase). To prove the cholesteric pattern of ds DNA molecules in this phase, the “liquid-like” state of the dispersion particles was transformed into its “rigid” counterpart.