Anisotropic Liquid Research Articles

Frequency-controlled dielectrophoresis-driven wetting of nematic liquid crystals

We show that surface-localized dielectrophoresis-driven wetting of anisotropic nematic liquid crystal sessile droplets obeys the same relationship, , which has previously been found for isotropic liquid droplets, even though the nematic liquid crystal phase possesses a uniaxial dielectric permittivity tensor. We also demonstrate that the dielectrowetting coefficient , which determines the magnitude of the reduction in the contact angle, from to , through the action of a potential difference , can be controlled by the frequency of the applied voltage between interdigitated electrodes beneath a droplet of highly dispersive nematic liquid crystal. Our Q-tensor modelling of the electric field-induced 2-dimensional n-director distortions within a nematic droplet elucidates how this linear relationship holds for voltages when exceeds 3°–4°.

Controllable Directional Liquid Transport in Open Channel

AbstractDirectional liquid transport has gradually drawn worldwide attention due to its diverse potential applications in precision medicine, microfluidics, and microreactors. However, previous directional liquid control usually resorts to complex hierarchical micro‐nano structures, heterogeneous wettability, or external driving fields, which inevitably limits the flexibility and applicability of liquid manipulation. Here, a novel open channel surface is presented, which exhibits an on‐demand directional transport performance via a shifting mechanism of weak area on liquid precursor. The coupling effect of sidewall wettability and bottom hydrophobic barrier patterns redistributes the surface pressure from the front and rear meniscus of liquid precursor, which determine the position of weak area and transport direction. The impacts of wettability and various barrier patterns on anisotropic liquid transport ability are made clear, and the design principle of unidirectional open channels without complex microstructure is validated. Smart directional transport can also be easily built by use of various stimulus materials, such as thermal responsive polymer. This controllable directional liquid transport can introduce ways for various on‐demand liquid manipulations.

A Programmable Liquid Crystal Elastomer Metamaterials With Soft Elasticity.

Liquid crystal elastomers (LCEs) are a rubbery network of polymers with ordered liquid crystal mesogens. The combination of rubber elasticity and the anisotropic liquid crystalline order gives exceptional mechanical properties, like soft elasticity, where near-constant stress accompanies large elastic deformation in the material. However, the soft elasticity in LCEs is often bounded by the intrinsic molecular interactions and structures, limiting the range of programmable mechanical properties and functionalities. Here, we demonstrate that the semi-soft elasticity of LCEs can be integrated into the framework of metamaterials to realize markedly programmabilities. Under uniaxial deformation, each state of the building blocks in metamaterials and the molecular composition of the nematic LCEs is associated with a distinctly different stress-strain relation that is fully elastic. Taking advantage of the tunable bending and stretching deformation enabled by the geometry of the building blocks and the semi-soft elasticity of the nematic LCE in the metamaterials, we can engineer the local stretch and stress at an unmet level of their counterpart composed by elastomers. Numerical simulations and analytical models are developed to relate the metamaterial geometries and the LCE soft elasticity to the mechanical responses. In addition, an elastic region with near-zero stiffness up to a stretch of 1.4 can be designed by connecting the compliant responses due to bending deformation and the soft elasticity in the LCE. We expect that the specialized mechanical tunability enabled by the LCE metamaterials can facilitate the development of advanced forms of mechanical metamaterials and impact the design of robotic systems.

Self‐Assembly of Helical Polymers and Oligomers to Create Liquid Crystalline Alignment for Anisotropic NMR Parameters

The measurement of anisotropic residual dipolar couplings (RDCs) parameters for the structure elucidation of organic molecules relies on suitable alignment media. Employment of self-assembled liquid crystalline systems to create anisotropic alignment can be an effective way to realize aligned samples and acquire RDCs. This Mini-review highlights the recent advances on amino acid-based helical polymers and supramolecular oligomers forming rigid, rod-like structures that aggregate into ordered liquid crystalline phases, including amino acid-based helical polyisocyanides, polyacetylenes, polypeptides, and oligopeptides assembled alignment media. The methodology for the determination of anisotropic liquid crystals is briefly discussed, and a summary of recent research progress in the enantiodifferentiation of helical polymers aligned media is followed. In addition, the self-assembled mechanism of oligopeptides and their RDCs structural analysis are also described.

Ultraslippery/hydrophilic patterned surfaces for efficient fog harvest

The rapid and controllable sliding of droplets on anisotropic slippery liquid infused porous surfaces (SLIPS) has promising application prospects in the fields of energy, lab-on-a-chip, etc. In this work, the fabrication of hydrophilic patterned SLIPS on copper substrates that can achieve efficient droplet transport and fog harvest was reported. A single superhydrophilic stripe and array of superhydrophilic stripes were fabricated on SLIPS background, respectively. Contact angles, sliding angles and contact angle hysteresis of the surfaces were investigated and analyzed. Results showed that hydrophilic patterned SLIPS with superhydrophilic stripe array had remarkable anisotropy in contact angle hysteresis in the parallel and perpendicular directions due to the large energy barrier induced by liquid surface tension in the direction perpendicular to the stripes, which can be used to transport droplets rapidly and precisely. In addition, the fog harvest performance, as a typical example of droplet transport, was significantly improved on hydrophilic patterned SLIPS due to high nucleation density on the hydrophilic SLIPS, high condensate mobility, efficient condensate transferring from SLIPS to superhydrophilic stripes and liquid shedding along the stripes for departing.

Unravelling the anisotropic wetting properties of banana leaves with water and human urine

We report the heterogeneous and anisotropic wetting behaviors of Banana (Musa) leaves on adaxial (top) and abaxial (bottom) surfaces with water and human urine. Both surfaces comprise of varying number densities of micro ridges, micro stomata, micro flakes and nano hairs while the adaxial surface also constitutes discrete visible crest lines. The Wenzel roughness on abaxial and non-crest adaxial are 1.5 ± 0.05 and 1.18 ± 0.008, respectively as measured by combining optical profilometry and atomic force microscopy. A key scientific development in this work is to incorporate the measured Wenzel roughness in the surface energy estimations using Neumann's, Owens-Wendt-Rabel-Kaelble (OWRK) and Wu's models. The surface energy is 29 ± 2 mJ/m2 (OWRK) and 26 ± 1 mJ/m2 (Wu) on the adaxial surface. Nevertheless, the abaxial surfaces are characterized by smaller surface energy values of 20 ± 4 mJ/m2 (OWRK) and 24 ± 3 mJ/m2 (Wu). The measured static contact angles with water and urine are 110 ± 4° and 88 ± 4° (crest line), 130 ± 4° and 107 ± 5° (non-crest adaxial), 121 ± 4° and 120 ± 2° (abaxial) indicating hydrophobicity and urine-phobicity. The water droplets (2.5 to 10 µl) exhibited anisotropic dynamic wettability as they only rolled off parallel to the micro-ridges but stuck when slid perpendicular to the ridges even for specimen tilts up to 90°. Thus, this study unravels the anisotropic wettability of banana leaves due to the presence of micro-ridges which can be biomimicked for providing anisotropic liquid gliding. Also, this can aid in designing the spraying conditions of urine as a natural pesticide/fertilizer in the banana orchards.

Инфляция вблизи максимума потенциала для космологической модели с вращением

The first stage of inflation for the Bianchi type IX metric is considered for the case of inflation near the potential maximum. The rotation of the dark energy evolution is investigated, where the dark energy is an anisotropic liquid. The dependence of the scale factor on time coincides with a similar dependence in Friedman cosmology at all stages of Friedman evolution in the consideration solution. There will be an accelerated expansion of the universe at a later time.

Advances in 4D printing of liquid crystalline elastomers: materials, techniques, and applications.

Liquid crystalline elastomers (LCEs) are polymer networks exhibiting anisotropic liquid crystallinity while maintaining elastomeric properties. Owing to diverse polymeric forms and self-alignment molecular behaviors, LCEs have fascinated state-of-the-art efforts in various disciplines other than the traditional low-molar-mass display market. By patterning order to structures, LCEs demonstrate reversible high-speed and large-scale actuations in response to external stimuli, allowing for close integration with 4D printing and architectures of digital devices, which is scarcely observed in homogeneous soft polymer networks. In this review, we collect recent advances in 4D printing of LCEs, with emphases on synthesis and processing methods that enable microscopic changes in the molecular orientation and hence macroscopic changes in the properties of end-use objects. Promising potentials of printed complexes include fields of soft robotics, optics, and biomedical devices. Within this scope, we elucidate the relationships among external stimuli, tailorable morphologies in mesophases of liquid crystals, and programmable topological configurations of printed parts. Lastly, perspectives and potential challenges facing 4D printing of LCEs are discussed.

Distinguishing viscous, ballistic, and diffusive current flows in anisotropic metals

We show that in anisotropic Fermi liquids where momentum-conserving scattering is much faster than momentum-relaxing scattering processes, local imaging of the electric current flow patterns can cleanly distinguish between ballistic, viscous and ohmic flow patterns simultaneously (using a single image). We propose using multi-layer graphene-based heterostructures, including ABA trilayer graphene, as a natural experimental platform where an anisotropic ballistic-to-viscous crossover may be visible in near-term experiments. Such experiments could lead to more direct measurements of momentum-conserving scattering lengths in electronic Fermi liquids.

Realizing Optical Persistent Spin Helix and Stern-Gerlach Deflection in an Anisotropic Liquid Crystal Microcavity.

Spin-orbit interactions which couple the spin of a particle with its momentum degrees of freedom lie at the center of spintronic applications. Of special interest in semiconductor physics are Rashba and Dresselhaus spin-orbit coupling. When equal in strength, the Rashba and Dresselhaus fields result in SU(2) spin rotation symmetry and emergence of the persistent spin helix only investigated for charge carriers in semiconductor quantum wells. Recently, a synthetic Rashba-Dresselhaus Hamiltonian was shown to describe cavity photons confined in a microcavity filled with optically anisotropic liquid crystal. In this Letter, we present a purely optical realization of two types of spin patterns corresponding to the persistent spin helix and the Stern-Gerlach experiment in such a cavity. We show how the symmetry of the Hamiltonian results in spatial oscillations of the spin orientation of photons traveling in the plane of the cavity.

Rethinking Figure-of-Merits of Liquid Crystals Shielded Coplanar Waveguide Phase Shifters at 60 GHz

The demand for reconfigurable millimetre-wave (mm-Wave) components based on highly anisotropic liquid crystals (LC) is higher than ever before for the UK and worldwide. In this work, 60 GHz investigation on a bespoke shielded coplanar waveguide (SCPW) phase shifter structure filled with 16 types of microwave-enabled nematic LCs respectively indicates that the patterns of the device’s figure-of-merit (FoM, defined as the ratio of maximum differential phase shift to maximum insertion loss) reshuffle from those of the characterised LC materials’ FoM (defined as the ratio of tunability to maximum dissipation factor). To be more specific, GT7-29001- and MDA-03-2838-based phase shifters exhibit the highest FoM for devices, outperforming phase shifters based on GT5-28004 and TUD-566 with the highest FoM for materials. Such a mismatch between the device’s FoM and LC’s FoM implies a nonlinearly perturbed wave-occupied volume ratio effect. Furthermore, the relationship between insertion loss and the effective delay line length is nonlinear, as evidenced by measurement results of two phase shifters (0–π and 0–2π, respectively). Such nonlinearities complicate the established FoM metrics and potentially lead to a renewed interest in the selection and material synthesis of LCs to optimise reconfigurable mmWave devices, and promote their technological exploitation in phased array systems targeting demanding applications such as inter-satellite links and satellite internet.

Active terahertz spin state and optical chirality in liquid crystal chiral metasurface

Dynamic control of photonic spin state and chirality plays a vital role in various applications, such as polarization control, polarization-sensitive imaging, and biosensing. Here, we present a scheme for the flexible and dynamic manipulation of terahertz spin state conversion and optical chirality by combining two achiral structures: an asymmetric metasurface and a layer of anisotropic liquid crystal. The proposed asymmetric metasurface can realize the polarization conversion effect. For the circularly polarized incidence, it exhibits the asymmetric transmission of the spin-flipped states but no spin-locked optical chirality since its geometry is mirror symmetric along with the wave propagation. The introduction of the liquid crystal makes the composite metasurface not only exhibit the spin state conversion but also spin-locked chirality and spin-flipped chirality on account of breaking mirror symmetry, which realizes an electrically active terahertz chiral device. The experimental results show that the asymmetric transmission of the terahertz spin states can be dynamically manipulated, resulting in a large controllable range 83.8% to \ensuremath{-}30.7% of spin-locked circular dichroism at 0.76 THz and \ensuremath{-}98.2% to 44.7% of spin-flipped circular dichroism at 0.73 THz. This work paves the way for the development of terahertz meta devices capable of enabling active photonic spin state and chirality manipulation.

Numerical method for the equilibrium configurations of a Maier-Saupe bulk potential in a Q-tensor model of an anisotropic nematic liquid crystal

We present a numerical method, based on a tensor order parameter description of a nematic phase, that allows fully anisotropic elasticity. Our method thus extends the Landau-de Gennes Q-tensor theory to anisotropic phases. A microscopic model of the nematogen is introduced (the Maier-Saupe potential in the case discussed in this paper), combined with a constraint on eigenvalue bounds of Q. This ensures a physically valid order parameter Q (i.e., the eigenvalue bounds are maintained), while allowing for more general gradient energy densities that can include cubic nonlinearities, and therefore elastic anisotropy. We demonstrate the method in two specific two dimensional examples in which the Landau-de Gennes model including elastic anisotropy is known to fail, as well as in three dimensions for the cases of a hedgehog point defect, a disclination line, and a disclination ring. The details of the numerical implementation are also discussed.

Reconfigurable Surfaces Using Fringing Electric Fields from Nanostructured Electrodes in Nematic Liquid Crystals

AbstractLiquid crystals with a varying phase profile enable reconfigurable and intelligent devices to be designed, which are capable of manipulating incident electromagnetic fields in display, telecommunications as well as wearable applications. The active control of defects in these devices is becoming more important, especially since the electrodes used to manipulate them are shrinking to nanometer length scales. In this paper, a simple subwavelength, 1D, interdigitated metal electrode structure that can be reconfigured using nematic liquid crystals aligned in the homeotropic, planar, and hybrid methods are demonstrated. Accurate electro‐optic modeling of the directors and the defects are shown, which are induced by the fringing electric fields. Applied voltages result in liquid crystal reorientation near the bottom surface, such that defects are induced between the electrodes. The height of the electrodes does not affect the lateral position of these defects. Rather, this can be achieved by increasing the biasing voltage on the top electrode, which also leads to greater splay‐bend in the bulk of the material. These results therefore aim to generalize the control of defects in complex anisotropic nematic liquid crystals using simple interdigitated structures for a range of reconfigurable intelligent surface applications.

Liquid Crystal Elastomers for Biological Applications

The term liquid crystal elastomer (LCE) describes a class of materials that combine the elastic entropy behaviour associated with conventional elastomers with the stimuli responsive properties of anisotropic liquid crystals. LCEs consequently exhibit attributes of both elastomers and liquid crystals, but additionally have unique properties not found in either. Recent developments in LCE synthesis, as well as the understanding of the behaviour of liquid crystal elastomers—namely their mechanical, optical and responsive properties—is of significant relevance to biology and biomedicine. LCEs are abundant in nature, highlighting the potential use of LCEs in biomimetics. Their exceptional tensile properties and biocompatibility have led to research exploring their applications in artificial tissue, biological sensors and cell scaffolds by exploiting their actuation and shock absorption properties. There has also been significant recent interest in using LCEs as a model for morphogenesis. This review provides an overview of some aspects of LCEs which are of relevance in different branches of biology and biomedicine, as well as discussing how recent LCE advances could impact future applications.

Inelastic Interactions of Solitons in a Linear Defect of the Electroconvective Structure of a Nematic Liquid Crystal

The inelastic interactions of solitons in a linear defect appearing in a one-dimensional electroconvective structure of a π/2-twisted nematic liquid crystal have been studied for the first time. Linear defects in twisted nematic liquid crystals are characterized by a sufficiently extended strain field and are oriented normally to Williams domains. Hydrodynamic flows in domains have not only the tangential velocity component but also the axial component whose directions in neighboring domains are opposite. In contrast to the case of planar orientation, the flow continuity condition for an anisotropic liquid in twisted nematic liquid crystals prevents the decay of a linear defect into individual dislocations when an applied voltage increases. This behavior results in the formation of domain zigzag oscillations in the defect core. The boundaries between zig and zag regions are dislocations with the topological charges S = +1 and –1. It has been established that the periodic interaction of dislocations (kinks) with opposite topological charges S = +1 and –1 is accompanied by the formation of a breather. It has been found that the collision of a kink and the breather in the linear defect is inelastic because it leads to the decay of the breather into a kink–antikink pair. It has been shown that such interactions of dislocations with topological charges S = +1 and –1 are qualitatively well described by the perturbed sine-Gordon equation.

Determination of Young's Modulus of Active Pharmaceutical Ingredients by Relaxation Dynamics at Elevated Pressures.

A new approach is theoretically proposed to study the glass transition of active pharmaceutical ingredients and a glass-forming anisotropic molecular liquid at high pressures. We describe amorphous materials as a fluid of hard spheres. Effects of nearest neighbor interactions and cooperative motions of particles on glassy dynamics are quantified through a local and collective elastic barrier calculated using the elastically collective nonlinear Langevin equation theory. Inserting two barriers into Kramer's theory gives the structural relaxation time. Then, we formulate a new mapping based on the thermal expansion process under pressure to intercorrelate particle density, temperature, and pressure. This analysis allows us to determine the pressure and temperature dependence of α relaxation. From this, we estimate the effective elastic modulus of amorphous materials and capture the effects of conformation on the relaxation process. Remarkably, our theoretical results agree well with experiments.

Tunable optical properties for ORW e-paper

ABSTRACT Reflective liquid crystal displays are attracting attention as portable information systems because of zero- or extremely low power consumption. In this study, we deal with an electrode-free reflective liquid crystal cell, where image formation is achieved by coating one of the substrates with optically active azo dye thin film. To describe reflective characteristics of the cell, we develop a simulation model based on a continuum theory with the successive solution of the Maxwell equations for light propagating in anisotropic liquid crystal media. Computation of reflective characteristics was carried out by using the 8 × 8 transfer matrix method, which is the solution of Maxwell equations. By changing boundary conditions, we have obtained different reflectance coefficients (from ~0.03 to 0.43), and the corresponding chromatic colours were generated. Our results were obtained by using the modelling and optimisation system MOUSE-LCD.

Birefringent optofluidic gratings.

A set of parallel microfluidic channels behaving as a diffraction grating operating in the Raman-Nath regime has been fabricated and studied. The diffraction efficiency of such structure can be tuned by selecting a liquid with a particular refractive index and/or optical anisotropy. Alternatively the optical properties of the liquid can be characterised by measuring the diffraction efficiency and the state of polarization of the diffracted beam. In this work, the microfluidic channels under study have been filled with penicillin molecules dissolved in water. Due to the chirality of the penicillin, the liquid has been found to have circular birefringence of 2.14 × 10-7. The addition of the anisotropic liquid modifies the polarization properties of the microfluidic diffraction grating. The diffraction efficiency of the grating has been characterised for different probe beam wavelengths and states of polarization. Currently the diffraction efficiency of the device is low - 1.7%, but different approaches for its improvement have been discussed.

Inflationary Model of the Universe with a Type IX Metric and Possibility of Its Quantum Birth

Within the framework of the general theory of relativity, an anisotropic cosmological model with expansion and rotation with a Bianchi type IX metric is constructed. The first stage of inflation of a Universe filled with a scalar field and an anisotropic liquid is considered. The Wheeler–De Witt equation is obtained, and the possibility of minisuperspace quantization is investigated.