Half-integer topological defects paired via string micelles in polar liquids.

Ferroelectric nematic (N) liquid crystals present a compelling platform for exploring topological defects in polar fields, while their structural properties can be significantly altered by ionic doping. In this study, we demonstrate that doping the ferroelectric nematic material RM734 with cationic polymers enables the formation of polymeric micelles that connect pairs of half-integer topological defects. Polarizing optical microscopy reveals that these string defects exhibit butterfly textures, featured with a 2D polarization field divided by Néel-type kink walls into domains exhibiting either uniform polarization or negative splay and bend deformations.

Chiral π domain walls composed of twin half-integer surface disclinations in ferroelectric nematic liquid crystals.

Ferroelectric nematic liquid crystals are polar fluids characterized by microscopic orientational ordering and macroscopic spontaneous polarizations. Within these fluids, domain walls that separate regions of different polarizations are ubiquitous. We demonstrate that the π walls in films of the polar fluids consist of twin half-integer surface disclinations spaced horizontally, enclosing a subdomain where the polarization exhibits left- or right-handed π twists across the film.

Ultra-high spatial resolutions in photopatterning molecular orientations.

Accurately aligning liquid crystal molecules into predetermined spatially variant orientations is crucial for fabricating devices such as flat optical elements, soft actuators and robots. Despite the developments of various photopatterning techniques for this purpose, the limits of their spatial resolutions have been rarely addressed. In this study, we delve into the physical constraints governing the spatial resolutions of two prominent photopatterning methods: single exposure to light fields with structured polarizations and multi-exposures to light fields with structured intensities.

Q-switched Nd:YVO laser operating at 1064 nm with NiPS nanoflakes onto a silica metasurface as saturable absorbers.

In this work, we show that a metasurface can be used to improve the performance of the two-dimensional (2D) material saturable absorber in a Nd:YVO solid-state laser. To our knowledge, the hybrid saturable absorber was fabricated by spraying the NiPS nanoflakes onto a silica metasurface for the first time. It is shown that the optical absorption, modulation depth, saturation intensity, and ultrafast recovery time of the metasurface-NiPS saturable absorber exhibit better performance than the 2D material control device.

Nematic-isotropic phase transitions in thin slabs of liquid crystals with topological defect arrays.

We study the nematic-to-isotropic phase transitions in thin slabs of nematic liquid crystals with photopatterned director fields of topological defect arrays at constant heating rates and show that the transition kinetics is significantly impacted by both the heating rate and the topological strengths of these defects. Specifically, with ±1/2 defect arrays, the isotropic domains emerge from the defect cores when the heating rate is high, while from random places when the heating rate is low. With ±1 defect arrays, the isotropic domains always emerge from the defect cores regardless of the heating rate.

Adaptations for gas exchange enabled the elongation of lepidopteran proboscises.

The extensive biodiversification of butterflies and moths (Lepidoptera) is partly attributed to their unique mouthparts (proboscis [Pr]) that can span in length from less than 1 mm to over 280 mm in Darwin's sphinx moths. Lepidoptera, similar to other insects, are believed to inhale and exhale respiratory gases only through valve-like spiracles on their thorax and abdomen, making gas exchange through the narrow tracheae (Tr) challenging for the elongated Pr. How Lepidoptera overcome distance effects for gas transport to the Pr is an open question that is important to understanding how the Pr elongated over evolutionary time.

Optical Imaging and High-Accuracy Quantification of Intracellular Iron Contents.

Precise quantification of intracellular iron contents is important to biomedical applications of magnetic nanoparticles. Current approaches for iron quantification rely on specialized instruments while most only yield iron quantities averaged over plenty of cells. Here, a simple and robust approach, combining digital optical microscopy with the Beer-Lambert's law, that allows for imaging stainable iron distribution in individual cells and the quantification of stainable iron contents with an unprecedented accuracy of femtogram per pixel, is presented.

Topology control of human fibroblast cells monolayer by liquid crystal elastomer.

Eukaryotic cells in living tissues form dynamic patterns with spatially varying orientational order that affects important physiological processes such as apoptosis and cell migration. The challenge is how to impart a predesigned map of orientational order onto a growing tissue. Here, we demonstrate an approach to produce cell monolayers of human dermal fibroblasts with predesigned orientational patterns and topological defects using a photoaligned liquid crystal elastomer (LCE) that swells anisotropically in an aqueous medium.

Thermophoresis of colloids in nematic liquid crystal.

Thermophoresis, or the directional motion of colloidal particles in liquids driven by a temperature gradient, is of both fundamental interest and practical use. In this work we explore the thermophoresis of colloids suspended in nematic liquid crystals (LCs). We observe that the motion of these colloids is fundamentally different from that in isotropic systems as a result of elastic distortions in the director fields caused by the colloidal inclusions.

Influence of treating parameters on thermomechanical properties of recycled epoxy-acid vitrimers.

Vitrimers have the characteristics of shape-reforming and surface-welding, and have the same excellent mechanical properties as thermosets; so vitrimers hold the promise of a broad alternative to traditional plastics. Since their initial introduction in 2011, vitrimers have been applied to many unique applications such as reworkable composites and liquid crystal elastomer actuators. A series of experiments have investigated the effects of reprocessing conditions (such as temperature, time, and pressure) on recycled materials.

Controlled Placement of Microparticles at the Water-Liquid Crystal Elastomer Interface.

Controlled placement of microparticles is of prime importance in production of microscale superstructures. In this work, we demonstrate the remote control of microparticle placement using a photoactivated surface profile of a liquid crystal elastomer (LCE) coating. We employ light-responsive LCEs with preimposed patterns of molecular orientation (director) in the plane of coating.

Low f-Number Diffraction-Limited Pancharatnam-Berry Microlenses Enabled by Plasmonic Photopatterning of Liquid Crystal Polymers.

Microlenses are desired by a wide range of industrial applications while it is always challenging to make them with diffraction-limited quality. Here, it is shown that high-quality microlenses based on Pancharatnam-Berry (PB) phases can be made with liquid crystal polymers by using a plasmonic photopatterning technique. Based on the generalized Snell's law for the PB phases, PB microlenses with a range of focal lengths and f-numbers are designed and fabricated and their point-spread functions and ability to image micrometer-sized particles are carefully characterized.

Microplastic surface properties affect bacterial colonization in freshwater.

Microplastics are a global concern in aquatic ecology and are readily colonized by bacteria in the environment. There is a lack of information on bacterial colonization of eroded and un-eroded microplastics in freshwater. In this study, six types of microplastics were incubated for 8 weeks in microcosms with water from Lake Erie.

Author Correction: Liquid crystal elastomer coatings with programmed response of surface profile.

The original version of this Article contained errors in Figs. 1a, 2a, 3a, and 4b, in which the units on the scale bars incorrectly read 'µm' rather than the correct 'nm.' This has been corrected in both the PDF and HTML versions of the Article.

Liquid crystal elastomer coatings with programmed response of surface profile.

Stimuli-responsive liquid crystal elastomers with molecular orientation coupled to rubber-like elasticity show a great potential as elements in soft robotics, sensing, and transport systems. The orientational order defines their mechanical response to external stimuli, such as thermally activated muscle-like contraction. Here we demonstrate a dynamic thermal control of the surface topography of an elastomer prepared as a coating with a pattern of in-plane molecular orientation.

The Ingestion of Fluorescent, Magnetic Nanoparticles for Determining Fluid-uptake Abilities in Insects.

Fluid-feeding insects ingest a variety of liquids, which are present in the environment as pools, films, or confined to small pores. Studies of liquid acquisition require assessing mouthpart structure and function relationships; however, fluid uptake mechanisms are historically inferred from observations of structural architecture, sometimes unaccompanied with experimental evidence. Here, we report a novel method for assessing fluid-uptake abilities with butterflies (Lepidoptera) and flies (Diptera) using small amounts of liquids.

Patterning of Lyotropic Chromonic Liquid Crystals by Photoalignment with Photonic Metamasks.

Controlling supramolecular self-assembly in water-based solutions is an important problem of interdisciplinary character that impacts the development of many functional materials and systems. Significant progress in aqueous self-assembly and templating has been demonstrated by using lyotropic chromonic liquid crystals (LCLCs) as these materials show spontaneous orientational order caused by unidirectional stacking of plank-like molecules into elongated aggregates. In this work, it is demonstrated that the alignment direction of chromonic assemblies can be patterned into complex spatially-varying structures with very high micrometer-scale precision.

Mouthpart conduit sizes of fluid-feeding insects determine the ability to feed from pores.

Fluid-feeding insects, such as butterflies, moths and flies (20% of all animal species), are faced with the common selection pressure of having to remove and feed on trace amounts of fluids from porous surfaces. Insects able to acquire fluids that are confined to pores during drought conditions would have an adaptive advantage and increased fitness over other individuals. Here, we performed feeding trials using solutions with magnetic nanoparticles to show that butterflies and flies have mouthparts adapted to pull liquids from porous surfaces using capillary action as the governing principle.

Command of active matter by topological defects and patterns.

Self-propelled bacteria are marvels of nature with a potential to power dynamic materials and microsystems of the future. The challenge lies in commanding their chaotic behavior. By dispersing swimming Bacillus subtilis in a liquid crystalline environment with spatially varying orientation of the anisotropy axis, we demonstrate control over the distribution of bacterial concentration, as well as the geometry and polarity of their trajectories.

Controlling placement of nonspherical (boomerang) colloids in nematic cells with photopatterned director.

Placing colloidal particles in predesigned sites represents a major challenge of the current state-of-the-art colloidal science. Nematic liquid crystals with spatially varying director patterns represent a promising approach to achieve a well-controlled placement of colloidal particles thanks to the elastic forces between the particles and the surrounding landscape of molecular orientation. Here we demonstrate how the spatially varying director field can be used to control placement of non-spherical particles of boomerang shape.

Control of colloidal placement by modulated molecular orientation in nematic cells.

Colloids self-assemble into various organized superstructures determined by particle interactions. There is tremendous progress in both the scientific understanding and the applications of self-assemblies of single-type identical particles. Forming superstructures in which the colloidal particles occupy predesigned sites and remain in these sites despite thermal fluctuations represents a major challenge of the current state of the art.

Correction: Cholesteric liquid crystals in rectangular microchannels: skyrmions and stripes.

Correction for 'Cholesteric liquid crystals in rectangular microchannels: skyrmions and stripes' by Yubing Guo et al., Soft Matter, 2016, DOI: 10.1039/c6sm01190j.

Cholesteric liquid crystals in rectangular microchannels: skyrmions and stripes.

In this paper, we present experimental and numerical studies on the microstructures of a cholesteric liquid crystal (CLC) confined in rectangular micron-channels. By using a sequence of microfabrication techniques we fabricated the micro-sized channels with accurately controlled size, aspect ratio and homeotropic surface anchoring. Through optical microscopic studies we established a phase diagram for the liquid crystal defect textures as a function of the channel depth and width.

Effects of translation-rotation coupling on the displacement probability distribution functions of boomerang colloidal particles.

Prior studies have shown that low symmetry particles such as micro-boomerangs exhibit behaviour of Brownian motion rather different from that of high symmetry particles because convenient tracking points (TPs) are usually inconsistent with their center of hydrodynamic stress (CoH) where the translational and rotational motions are decoupled. In this paper we study the effects of the translation-rotation coupling on the displacement probability distribution functions (PDFs) of the boomerang colloid particles with symmetric arm length. By tracking the motions of different points on the particle symmetry axis, we show that as the distance between the TP and the CoH is increased, the effects of translation-rotation coupling becomes pronounced, making the short-time 2D PDF for fixed initial orientation to change from elliptical, to bean and then to crescent shape, and the angle averaged PDFs change from ellipsoidal-particle-like PDF to a shape with a Gaussian top and long displacement tails.

High-Resolution and High-Throughput Plasmonic Photopatterning of Complex Molecular Orientations in Liquid Crystals.

A plasmonic photopatterning technique is proposed and demonstrated for aligning the molecular orientation in liquid crystals (LCs) in patterns with designer complexity. Using plasmonic metamasks in which target molecular directors are encoded, LC alignments of arbitrary planar patterns can be achieved in a repeatable and scalable fashion withunprecedentedly high spatial resolution and high throughput.