High-Order Nonlinear Electrophoresis in a Nematic Liquid Crystal.

Electrophoresis is the motion of particles relative to a surrounding fluid driven by a uniform electric field. In conventional electrophoresis, the electrophoretic velocity grows linearly with the applied field. Nonlinear effects with a quadratic speed vs field dependence are gaining research interest since an alternating current field could drive them. Here, we report on the giant nonlinearity of electrophoresis in a nematic liquid crystal in which the speed grows with the fourth and sixth powers of the electric field. The mechanism is attributed to the shear thinning of the nematic environment induced by the moving colloid. The observed giant nonlinear effect dramatically enhances the efficiency of electrophoretic transport.

Tunable origami metastructure based on liquid crystal for curvature sensing.

In this paper, a liquid crystal (LC) tunable origami metastructure (OMS) designed for curvature sensing on cylindrical surfaces to measure their curvature is introduced. The LC employed is K15 (5CB) and the applicable band is 0.36∼23 GHz. When excited by electromagnetic waves (EMWs) within the 4∼16 GHz, the resonance frequency of the OMS shifts from 10.24 GHz to 10.144 GHz, corresponding to a change in absorption amplitude ranging from 0.773 to 0.920. In terms of curvature sensing, the detectable range of curvature spans from 0 to 0.327 mm-1. The maximum sensitivity (S) achieved for curvature measurement reaches 0.918/mm-1, accompanied by a quality factor (Q-factor) of 25.88. The proposed OMS embodies numerous excellent traits, including wide-range sensing capabilities and heightened S, promising for applications in bionic skin, smart robotics, and related fields.

Dynamically Modulating the Dissymmetry Factor of Circularly Polarized Organic Ultralong Room-Temperature Phosphorescence from Soft Helical Superstructures.

Achieving circularly polarized organic ultralong room-temperature phosphorescence (CP-OURTP) with a high luminescent dissymmetry factor (glum ) is crucial for diverse optoelectronic applications. In particular, dynamically controlling the dissymmetry factor of CP-OURTP can profoundly advance these applications, but it is still unprecedented. This study introduces an effective strategy to achieve photoirradiation-driven chirality regulation in a bilayered structure film, which consists of a layer of soft helical superstructure incorporated with a light-driven molecular motor and a layer of room-temperature phosphorescent (RTP) polymer. The prepared bilayered film exhibits CP-OURTP with an emission lifetime of 805 ms and a glum value up to 1.38. Remarkably, the glum value of the resulting CP-OURTP film can be reversibly controlled between 0.6 and 1.38 over 20 cycles by light irradiation, representing the first example of dynamically controlling the glum in CP-OURTP.

Circularly Polarized Organic Ultralong Room-Temperature Phosphorescence with A High Dissymmetry Factor in Chiral Helical Superstructures.

Long-lived room-temperature phosphorescence (RTP) of organic materials holds a significant potential for optical information. Circularly polarized organic ultralong room-temperature phosphorescence (CP-OURTP) with extremely high dissymmetry factor (glum ) values is even highly demanded and considerably challenging. Here, an effective strategy is introduced to realize CP-OURTP with an emission decay time of 735 ms and a glum value up to 1.49, which exceeds two orders of magnitude larger than previous records, through a system composed of RTP polymers and chiral helical superstructures. The system exhibits excellent stability under multiple cycles of photoirradiation and thermal treatment, and is further employed for information encryption based on optical multiplexing. The results are anticipated to lay the foundation for the development of CP-OURTP materials in advanced photonic applications.

Light Management of Metal Halide Scintillators for High-Resolution X-Ray Imaging.

The ever-growing need to inspect matter with hyperfine structures requires a revolution in current scintillation detectors, and the innovation of scintillators is revived with luminescent metal halides entering the scene. Notably, for any scintillator, two fundamental issues arise: Which kind of material is suitable and in what form should the material exist? The answer to the former question involves the sequence of certain atoms into specific crystal structures that facilitate the conversion of X-ray into light, whereas the answer to the latter involves assembling these crystallites into particular material forms that can guide light propagation toward its corresponding pixel detector. Despite their equal importance, efforts are overwhelmingly devoted to improving the X-ray-to-light conversion, while the material-form-associated light propagation, which determines the optical signal collected for X-ray imaging, is largely overlooked. This perspective critically correlates the reported spatial resolution with the light-propagation behavior in each form of metal halides, combing the designing rules for their future development.

Topological transformations of a nematic drop.

Morphogenesis of living systems involves topological shape transformations which are highly unusual in the inanimate world. Here, we demonstrate that a droplet of a nematic liquid crystal changes its equilibrium shape from a simply connected tactoid, which is topologically equivalent to a sphere, to a torus, which is not simply connected. The topological shape transformation is caused by the interplay of nematic elastic constants, which facilitates splay and bend of molecular orientations in tactoids but hinders splay in the toroids. The elastic anisotropy mechanism might be helpful in understanding topology transformations in morphogenesis and paves the way to control and transform shapes of droplets of liquid crystals and related soft materials.

Anapole-excited terahertz multifunctional spoof surface plasmon polariton directional Janus metastructures.

The anapole mode, in which a distinct radiationless electromagnetic (EM) response in artificial media can be achieved, has attracted significant attention and been regarded as a promising candidate to initiate novel avenues to control the intrinsic radiative losses in nanophotonics and plasmonics, whose current research studies mainly focus on the manipulation of the one-directional incident wave. To exploit the propagation characteristic of incident waves in anapole-excited (AE) media, a set of terahertz (THz) multifunctional Janus metastructures (JMSs) for the opposite linear-polarized (LP) light excitation is presented in this paper. By introducing the directional-selective spoof surface plasmon polariton (SSPP) excited by anapole mode, a metastructure rasorber (MSR) possessing an absorption band of 2-3.08 THz (42.5%) and a co-polarized transmission window of 3.77-5.55 THz (38.2%) for the forward normal-incident LP wave is attained. Furthermore, the integration of the MSR and a polarization-conversation structure (PCS) can be used to fabricate a multifunctional Janus metadevice thus achieving the integration of EM energy harvesting, the co-polarized transmission, and cross-polarized reflection of light with opposite propagation directions, i.e., an absorption band of 2.14-3.09 THz (36.3%) for the forward normal-incident LP wave, and a cross-polarized reflection band of 2.08-3.03 THz (37.2%) for the backward vertical-incident LP wave, while attaining an identical co-polarized transmission window of 3.95-5.2 THz (27.3%). Moreover, by utilizing the substantial field-localization properties of anapole modes supported by the nested opposite-directional SSPP with different sizes, the Janus metastructure absorber (JMA) can achieve non-overlapped absorption bands of 2.02-2.84 THz (33.7%) and 2.88-4.58 THz (45.6%) for the bidirectional normal-incident LP waves, respectively. A series of passive JMSs based on the anapole modes excited by the opposite-directional incident waves significantly extend the theoretical framework and application field of multipole electrodynamics, especially aimed at directional-selective management.

Self-assembled liquid crystal architectures for soft matter photonics.

Self-assembled architectures of soft matter have fascinated scientists for centuries due to their unique physical properties originated from controllable orientational and/or positional orders, and diverse optic and photonic applications. If one could know how to design, fabricate, and manipulate these optical microstructures in soft matter systems, such as liquid crystals (LCs), that would open new opportunities in both scientific research and practical applications, such as the interaction between light and soft matter, the intrinsic assembly of the topological patterns, and the multidimensional control of the light (polarization, phase, spatial distribution, propagation direction). Here, we summarize recent progresses in self-assembled optical architectures in typical thermotropic LCs and bio-based lyotropic LCs. After briefly introducing the basic definitions and properties of the materials, we present the manipulation schemes of various LC microstructures, especially the topological and topographic configurations. This work further illustrates external-stimuli-enabled dynamic controllability of self-assembled optical structures of these soft materials, and demonstrates several emerging applications. Lastly, we discuss the challenges and opportunities of these materials towards soft matter photonics, and envision future perspectives in this field.

Correction: Shear-induced polydomain structures of nematic lyotropic chromonic liquid crystal disodium cromoglycate.

Correction for 'Shear-induced polydomain structures of nematic lyotropic chromonic liquid crystal disodium cromoglycate' by Hend Baza et al., Soft Matter, 2020, 16, 8565-8576.

Shear-induced polydomain structures of nematic lyotropic chromonic liquid crystal disodium cromoglycate.

Lyotropic chromonic liquid crystals (LCLCs) represent aqueous dispersions of organic disk-like molecules that form cylindrical aggregates. Despite the growing interest in these materials, their flow behavior is poorly understood. Here, we explore the effect of shear on dynamic structures of the nematic LCLC, formed by 14 wt% water dispersion of disodium cromoglycate (DSCG). We employ in situ polarizing optical microscopy (POM) and small-angle and wide-angle X-ray scattering (SAXS/WAXS) to obtain independent and complementary information on the director structures over a wide range of shear rates. The DSCG nematic shows a shear-thinning behavior with two shear-thinning regions (Region I at [small gamma, Greek, dot above] < 1 s-1 and Region III at [small gamma, Greek, dot above] > 10 s-1) separated by a pseudo-Newtonian Region II (1 s-1 < [small gamma, Greek, dot above] < 10 s-1). The material is of a tumbling type. In Region I, [small gamma, Greek, dot above] < 1 s-1, the director realigns along the vorticity axis. An increase of [small gamma, Greek, dot above] above 1 s-1 triggers nucleation of disclination loops. The disclinations introduce patches of the director that deviates from the vorticity direction and form a polydomain texture. Extension of the domains along the flow and along the vorticity direction decreases with the increase of the shear rate to 10 s-1. Above 10 s-1, the domains begin to elongate along the flow. At [small gamma, Greek, dot above] > 100 s-1, the texture evolves into periodic stripes in which the director is predominantly along the flow with left and right tilts. The period of stripes decreases with an increase of [small gamma, Greek, dot above]. The shear-induced transformations are explained by the balance of the elastic and viscous energies. In particular, nucleation of disclinations is associated with an increase of the elastic energy at the walls separating nonsingular domains with different director tilts. The uncovered shear-induced structural effects would be of importance in the further development of LCLC applications.

Novel pathways of HIV latency reactivation revealed by integrated analysis of transcriptome and target profile of bryostatin.

The reactivation of HIV latency cell will be necessary to curing HIV infection. Although many latency-reversal agents (LRAs) have proven effective to reactivate the latency cell, there is a lack of any systematic analysis of the molecular targets of these LRAs and related pathways in the context of transcriptome. In this study, we performed an integrated analysis of the target profile of bryostatin and transcriptome of the reactivated CD4+ T cells after exposing to bryostatin. The result showed a distinct gene expression profile between latency cells and bryostatin reactivated cells. We found bryostatin can target multiple types of protein other than only protein kinase C. Functional network analysis of the target profile and differential expressed genes suggested that bryostatin may activate a few novel pathways such as pyrimidine metabolism, purine metabolism and p53 signaling pathway, besides commonly known pathways DNA replication, cell cycle and so on. The results suggest that bryostatin may reactivate the HIV-latent cells through up-regulation of pyrimidine and purine metabolism or through starting the cell-cycle arrest and apoptosis induced by up-regulation of p53 signaling pathway. Our study provides some novel insights into the role of bryostatin and its affected pathways in controlling HIV latency and reactivation.

Cell alignment by smectic liquid crystal elastomer coatings with nanogrooves.

Control of cells behavior through topography of substrates is an important theme in biomedical applications. Among many materials used as substrates, polymers show advantages since they can be tailored by chemical functionalization. Fabrication of polymer substrates with nano- and microscale topography requires processing by lithography, microprinting, etching, and so forth. In this work, we introduce a different approach based on anisotropic elastic properties of polymerized smectic A (SmA) liquid crystal elastomer (LCE). When the SmA liquid crystal coating is deposited onto a substrate with planar alignment of the molecules, it develops nanogrooves at its free surface. After photopolymerization, these nanogrooves show an excellent ability to align human dermal fibroblasts over large areas. The alignment quality is good for both bare SmA LCE substrates and for substrates coated with fibronectin. The SmA LCE nano-topographies show a high potential for tissue engineering.

Visible-Light-Driven Halogen Bond Donor Based Molecular Switches: From Reversible Unwinding to Handedness Inversion in Self-Organized Soft Helical Superstructures.

Visible-light-driven molecular switches endowing reversible modulation of the functionalities of self-organized soft materials are currently highly sought after for fundamental scientific studies and technological applications. Reported herein are the design and synthesis of two novel halogen bond donor based chiral molecular switches that exhibit reversible photoisomerization upon exposure to visible light of different wavelengths. These chiral molecular switches induce photoresponsive helical superstructures, that is, cholesteric liquid crystals, when doped into the commercially available room-temperature achiral liquid crystal host 5CB, which also acts as a halogen-bond acceptor. The induced helical superstructure containing the molecular switch with terminal iodo atoms exhibits visible-light-driven reversible unwinding, that is, a cholesteric-nematic phase transition. Interestingly, the molecular switch with terminal bromo atoms confers reversible handedness inversion to the helical superstructure upon irradiation with visible light of different wavelengths. This visible-light-driven, reversible handedness inversion, enabled by a halogen bond donor molecular switch, is unprecedented.

Three-dimensional solitary waves with electrically tunable direction of propagation in nematics.

Production of stable multidimensional solitary waves is a grand challenge in modern science. Steering their propagation is an even harder problem. Here we demonstrate three-dimensional solitary waves in a nematic, trajectories of which can be steered by the electric field in a plane perpendicular to the field. The steering does not modify the properties of the background that remains uniform. These localized waves, called director bullets, are topologically unprotected multidimensional solitons of (3 + 2)D type that show fore-aft and right-left asymmetry with respect to the background molecular director; the symmetry is controlled by the field. Besides adding a whole dimension to the propagation direction and enabling controlled steering, the solitons can lead to applications such as targeted delivery of information and micro-cargo.

Dye-doped dual-frequency nematic cells as fast-switching polarization-independent shutters.

We present polarization-independent optical shutters with a sub-millisecond switching time. The approach utilizes dual-frequency nematics doped with a dichroic dye. Two nematic cells with orthogonal alignment are driven simultaneously by a low-frequency or high-frequency electric field to switch the shutter either into a transparent or a light-absorbing state. The switching speed is accelerated via special short pulses of high amplitude voltage. The approach can be used in a variety of electro-optical devices.

Publisher Correction: Electrically driven three-dimensional solitary waves as director bullets in nematic liquid crystals.

The original version of this article contained an error in the description of Supplementary Movie 7, which incorrectly read 'Collision resulting in annihilation of two solitons. U = 45.1 V, f = 600 Hz, T = 50 °C, d = 8.0 µm. The original movie is taken at the frame rate of 91 fps. The playback speed is 7 fps.' The correct version reads 'Death of a soliton at a dust particle. U = 65.6 V, f = 800 Hz, T = 50 °C, d = 7.7 µm. The original movie is taken at the frame rate of 92 fps. The playback speed is 7 fps.' The HTML has been updated to include a corrected version of the 'Description of Additional Supplementary Files' file.

Electrically driven three-dimensional solitary waves as director bullets in nematic liquid crystals.

Electric field-induced collective reorientation of nematic molecules is of importance for fundamental science and practical applications. This reorientation is either homogeneous over the area of electrodes, as in displays, or periodically modulated, as in electroconvection. The question is whether spatially localized three-dimensional solitary waves of molecular reorientation could be created. Here we demonstrate that the electric field can produce particle-like propagating solitary waves representing self-trapped "bullets" of oscillating molecular director. These director bullets lack fore-aft symmetry and move with very high speed perpendicularly to the electric field and to the initial alignment direction. The bullets are true solitons that preserve spatially confined shapes and survive collisions. The solitons are topologically equivalent to the uniform state and have no static analogs, thus exhibiting a particle-wave duality. Their shape, speed, and interactions depend strongly on the material parameters, which opens the door for a broad range of future studies.

Nanosecond switching of micrometer optical retardance by an electrically controlled nematic liquid crystal cell.

Electro-optic response of liquid crystals in mainstream display applications exhibits a millisecond switching of optical retardance on the order of one micrometer. We demonstrate that a similarly large optical retardance can be switched much faster, within 10-100 nanoseconds, by using multiple passes of light through a cell filled with the nematic liquid crystal. The fast response is based on the so-called nanosecond electric modification of order parameters (NEMOP) effect. The described approach can be used to develop ultrafast optical shutters and modulators.

Kerr effect at high electric field in the isotropic phase of mesogenic materials.

The well-known Kerr effect in isotropic fluids consists in the appearance of uniaxial orientational order and birefringence that grows as the square of the applied electric field. We predict and observe that at a high electric field, the Kerr effect displays features caused by the nonlinear dependence of dielectric permittivity on the field-induced orientational order parameter. Namely, the field-induced birefringence grows faster than the square of the electric field and the dynamics of birefringence growth slows down as the field increases. As a function of temperature, the field-induced birefringence is inversely proportional to the departure from an asymptotic critical temperature, but this temperature is no longer a constant (corresponding to the lower limit of the supercooled isotropic phase) and increases proportionally to the square of the electric field.

Nanosecond electro-optics of a nematic liquid crystal with negative dielectric anisotropy.

We study a nanosecond electro-optic response of a nematic liquid crystal in a geometry where an applied electric field E modifies the tensor order parameter but does not change the orientation of the optic axis (director N ̂). We use a nematic with negative dielectric anisotropy with the electric field applied perpendicularly to N ̂. The field changes the dielectric tensor at optical frequencies (optic tensor) due to the following mechanisms: (a) nanosecond creation of the biaxial orientational order, (b) uniaxial modification of the orientational order that occurs over time scales of tens of nanoseconds, and (c) the quenching of director fluctuations with a wide range of characteristic times up to milliseconds. We develop a model to describe the dynamics of all three mechanisms. We design the experimental conditions to selectively suppress the contributions from the quenching of director fluctuations (c) and from the biaxial order effect (a) and thus, separate the contributions of the three mechanisms in the electro-optic response. As a result, the experimental data can be well fitted with the model parameters. The analysis provides a rather detailed physical picture of how the liquid crystal responds to a strong electric field on a time scale of nanoseconds. The paper provides a useful guidance in the current search for the biaxial nematic phase. Namely, the temperature dependence of the biaxial susceptibility allows one to estimate the temperature of the potential uniaxial-to-biaxial phase transition. An analysis of the quenching of director fluctuations indicates that on a time scale of nanoseconds, the classic model with constant viscoelastic material parameters might reach its limit of validity. The effect of nanosecond electric modification of the order parameter can be used in applications in which one needs to achieve ultrafast (nanosecond) changes in optical characteristics, such as birefringence.