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Polar crystal surfaces play an important role in the functionality of many materials and have been studied extensively over many decades. In this article, a theoretical framework is presented that extends existing theories by placing the surrounding solution environment on an equal footing with the crystal itself; this is advantageous, e.g., when considering processes such as crystal growth from solution. By considering the polar crystal as a stack of parallel plate capacitors immersed in a solution environment, the equilibrium adsorbed surface charge density is derived by minimizing the free energy of the system. In analogy to the well-known diverging surface energy of a polar crystal surface at zero temperature, for a crystal in solution it is shown that the "polar catastrophe" manifests as a diverging free energy cost to perturb the system from equilibrium. Going further than existing theories, the present formulation predicts that fluctuations in the adsorbed surface charge density become increasingly suppressed with increasing crystal thickness. We also show how, in the slab geometry often employed in both theoretical and computational studies of interfaces, an electric displacement field emerges as an electrostatic boundary condition, the origins of which are rooted in the slab geometry itself, rather than the use of periodic boundary conditions. This aspect of the work provides a firmer theoretical basis for the recent observation that standard "slab corrections" fail to correctly describe, even qualitatively, polar crystal surfaces in solution. [ABSTRACT FROM AUTHOR]

Rapid surface charge mapping of a solid surface remains a challenge. In this study, we present a novel microchip based on liquid crystals for assessing the surface charge distribution of a planar or soft surface. This chip enables rapid measurements of the local surface charge distribution of a charged surface. The chip consists of a micropillar array fabricated on a transparent indium tin oxide substrate, while the liquid crystal is used to fill in the gaps between the micropillar structures. When an object is placed on top of the chip, the local surface charge (or zeta potential) influences the orientation of the liquid crystal molecules, resulting in changes in the magnitude of transmitted light. By measuring the intensity of the transmitted light, the distribution of the surface charge can be accurately quantified. We calibrated the chip in a three-electrode configuration and demonstrated the validity of the chip for rapid surface charge mapping using a borosilicate glass slide. This chip offers noninvasive, rapid mapping of surface charges on charged surfaces, with no need for physical or chemical modifications, and has broad potential applications in biomedical research and advanced material design. [ABSTRACT FROM AUTHOR]

It has become clear that superior material functions are derived from precisely controlled nanostructures. This has been greatly accelerated by the development of nanotechnology. The next step is to assemble materials with knowledge of their nano-level structures. This task is assigned to the post-nanotechnology concept of nanoarchitectonics. However, nanoarchitectonics, which creates intricate three-dimensional functional structures, is not always easy. Two-dimensional nanoarchitectonics based on reactions and arrangements at the surface may be an easier target to tackle. A better methodology would be to define a two-dimensional structure and then develop it into a three-dimensional structure and function. According to these backgrounds, this review paper is organized as follows. The introduction is followed by a summary of the three issues; (i) 2D to 3D dynamic structure control: liquid crystal commanded by the surface, (ii) 2D to 3D rational construction: a metal–organic framework (MOF) and a covalent organic framework (COF); (iii) 2D to 3D functional amplification: cells regulated by the surface. In addition, this review summarizes the important aspects of the ultimate three-dimensional nanoarchitectonics as a perspective. The goal of this paper is to establish an integrated concept of functional material creation by reconsidering various reported cases from the viewpoint of nanoarchitectonics, where nanoarchitectonics can be regarded as a method for everything in materials science. [ABSTRACT FROM AUTHOR]

Liquid crystal elastomers (LCEs) are becoming increasingly popular as a shape memory material for soft robot actuators that operate in a contractile or flexural mode. There have been previously studies on the use of LCEs for reversible changes in surface topography. However, surface protrusions have typically been limited to the order of 1 μm or depend on light, heat, or electrical stimulation that are difficult to locally control or require relatively high voltage. This article presents a novel operation mode of LCE actuators based on the wrinkling behavior of an LCE‐elastomer bilayer architecture. Embedding a liquid‐metal‐based conductive ink within the LCE enables electrical control of surface wrinkling through Joule heating. The actuator cells can generate wrinkles with amplitudes ranging from 17 to 45 μm within 30 s under an input power of 2 W and a voltage on the order of 1 V. As the bilayer is composed entirely of soft materials, it is highly deformable, flexible, and can be integrated into a multi‐cell array capable of bending on curved surfaces. [ABSTRACT FROM AUTHOR]

Sessile droplets of a ferroelectric nematic liquid crystalline material were exposed to surface electric fields produced by pyroelectric and photogalvanic (photovoltaic) effects in X-cut iron-doped lithium niobate crystals. The resulting dynamic processes were monitored by polarisation optical (video)microscopy (POM). During heating/cooling cycles, at first, the droplets change their shape from spherical to extended ellipsoidal. Then, they start to move rapidly along the surface electric field, i.e. along the crystal's polar axis (c-axis). During this motion, several droplets merge into running streams (tendrils) extending towards the edges of the top surface area. Finally, practically all liquid crystalline material is transported from the top surface to the side surfaces of the crystal. At stabilised temperatures, laser illumination of the assembly causes dynamic processes that are localised to the illuminated area. Also, in this case, the LC droplets merge into several tendril-like formations that are preferentially oriented along the c-axis of the crystal. The pattern of tendrils fluctuates with time, but it persists as long as the illumination is present. In this case, the LC material is transported between the central and the edge regions of the illuminated area. [ABSTRACT FROM AUTHOR]

Organic single crystals with low defect density are key functional materials for next‐generation electronics. Classical crystallization commonly results in a high density of molecular steps, which are defects that can trap charge carriers and reduce the mobility of organic semiconductors. Herein, a novel nonclassical crystallization mechanism involving nucleation, fusion, and growth is designed. The introduction of the fusion stage changes the crystal growth mode from three‐dimensional island growth to two‐dimensional layer‐by‐layer growth and leads to large‐area two‐dimensional molecular crystals with almost no molecular steps. Therefore, the average mobility is observed to improve from 1.26 to 2.07 cm2 V−1 s−1. The nonclassical crystallization mechanism paves the way for atomically flat single crystals to probe the intrinsic optoelectronic properties of organic semiconductors. [ABSTRACT FROM AUTHOR]

We demonstrated a two‐step tunable liquid crystal (LC) surface relief diffractive lens for presbyopia. The surface relief diffractive structure is fabricated by nano‐imprint lithography (NIL) roll‐to‐stage process. The LC lens is polarization‐independent with only one cholesteric liquid crystal (CLC) layer. The LC lens can be fabricated by LC one‐drop fill (ODF) process. This is useful for presbyopia vision correction. In this paper, we realized two‐step switched liquid crystal lens with optical power 0 and +2 diopters. [ABSTRACT FROM AUTHOR]

aligning surface for preorientation of low molecular weight liquid crystals in a bulk. The brush is built by grafting the polymer chains of a side-chain molecular architecture, with the side chains terminated by a chromophore unit mimicking the azobenzene unit, to a substrate. When irradiated with ultraviolet light, the chromophores photoisomerize into a non-mesogenic cis state and the whole system turns into an ordinary polymer brush with no orientationalorderandtwostates:thecollapsedandstraightenedone,dependingonthegraftingdensity.When irradiated with visible light, the chromophores photoisomerize into a mesogenic trans state, resulting in formationofatransientnetworkbetweenchainsbecauseofastrongattractionbetweenchromophores. Spontaneous self-assembly of the brush in these conditions results in an orientationally isotropic polydomain structure. The desired uniaxial planar ordering of chromophores within a brush can be achieved at certain temperature and grafting density intervals, as the result of a two-stage preparation protocol. An external stimulus orients chromophoresuniaxiallyatthefirststage. Thesystemisequilibratedatthesecondstageatagiventemperatureand with the external stimulus switched off. The preoriented chromophores either keep or loose their orientations depending on the strength of the memory effect inherent to a transient network of chains that are formed during the first stage, similarly to the case of the liquid crystalline elastomers, where such effects are caused by the covalent crosslinks. [ABSTRACT FROM AUTHOR]

In this paper, the growth rates of spherical and ellipsoidal crystals evolving in metastable melts and solutions are derived. Different scenarios and aspects of crystal growth (steady-state, unsteady-state, the phase transition temperature shift due to the curvature of the crystal surface and the kinetics of attaching atoms to it) are considered. The derived crystal growth laws under various process conditions are generalized and compared to experimental data. [ABSTRACT FROM AUTHOR]

In this study, a method to regulate the visible transmittance in off-state (Toff) and the contrast ratio (CR) for polymer-dispersed liquid crystals (PDLCs) via electrospinning polyvinyl alcohol (PVA) nanofibers on ITO surfaces in liquid crystal cells was reported. The PDLC samples were prepared in the conventional liquid crystal cells and in the nanofiber cells. The results indicated that the sample in the nanofiber cell presented a lower Toff and a larger CR in comparison with the sample in the conventional cell if the samples were prepared under the same UV light. [ABSTRACT FROM AUTHOR]

Atomically thin phases that crystallize on the surfaces of liquids above their melting point represent an emerging class of 2D crystals. Using AuSi as a model system, we show that their formation results in polycrystalline patterns that, unlike current generation 2D crystals, naturally coarsen as they form. The dynamics of the low-dimensional grain boundaries and their junctions is strongly coupled to the supporting liquid. The reorientation necessary for curvature driven interfacial kinetics entails diffusional dissipation with the liquid via mobile antisite defects, leading to a scale-independent power law dependence of the coarsening rate. Our study highlights natural thermal evolution of these polycrystals as a viable pathway for engineering the grain boundary networks in 2D surface crystals, motivating the search for a broader set of stable 2D surface crystals in multicomponent liquids and amorphous solids. [ABSTRACT FROM AUTHOR]

The liquid crystal alignments in the liquid crystal cell composed of the bare glass and indium tin oxide (ITO) regions are investigated based on birefringence. The experimental results by the proposed methods of circularly and linearly polarized light agree with the observation through the polarized optical microscope. The results show that the liquid crystal in the region of the bare glass is optical anisotropic and the liquid crystal director is almost parallel to the long side of the liquid crystal cell, while the liquid crystal in the region of ITO is isotropic. No other chemical components were found on the bare glass and ITO surfaces by the x-ray energy dispersive spectrometer, and the numerous random scratches on the bare glass were observed through the atomic force microscope. The self-consistent explanations for the different approaches and characteristic results are obtained. It is concluded that the bulk stress on the bare glass, rather than the local stress accompanied with the scratches, resulted in the liquid crystal alignment. Compared with the anisotropy of the bulk stress on the full bare glass, which formed during the preparation, the local stress on the scribed bare glass of the liquid crystal cell is isotropic. The scratch orientations are random, which cause the averaged local stress isotropic. The bulk stress on the long side is more significant than that on the short side of the cell. As a result, the liquid crystal director is almost parallel to the long side of the liquid crystal cell. The direction of the liquid crystal in the region of ITO is random, and the liquid crystal in that region is not birefringent. [ABSTRACT FROM AUTHOR]

Sonochemical synthesis of nano‐sized SrTiO3 carried out at close to room temperature, in ionic liquids (ILs) allows the tuning of particle size and particle morphology, that is, tracht and habitus, as well as particle aggregation via the choice of the ionic liquids (ILs) as the reaction medium. The nanoparticles demonstrate high performance for photocatalytic water splitting and photodecomposition of organic material. To this end bis(trifluoromethanesulfonyl)amide ([Tf2N]−)‐based ILs with cations of different properties with respect to specific interactions with the target material are investigated. Isolated, 15 ± 1 nm sized nano‐spheres of SrTiO3 are observed to form in [C3mimOH][Tf2N] ([C3mimOH]+ = 1‐(3‐hydroxypropyl)‐3‐methylimidazolium). Aggregation of small sized nanoparticles are observed to around 250 ± 100 nm large cube‐like formations in [C4mim][Tf2N] ([C4mim]+ = 1‐butyl‐3‐methylimidazolium), raspberry‐like in [C4Py][Tf2N] ([C4Py]+ butylpyridinium), and ball‐like in [P66614][Tf2N] ([P66614]+ tetradecyltrihexyl phosphonium). Importantly, the different materials show different performance as photocatalysts. SrTiO3 prepared in [C4mim][Tf2N] shows the highest photocatalytic activity for H2 evolution (1115.4 µmol h−1) when using 0.025 wt% Rh as the co‐catalyst, whereas the material prepared in [C3mimOH][Tf2N] shows the highest activity for the photocatalytic degradation of methylene blue (88%) under UV irradiation. The different photocatalytic activities can be correlated with the different crystal surface facets expressed in the respective nanosized SrTiO3 material, {110} for material obtained from [C4mim][Tf2N], and {100} for material from [C3mimOH][Tf2N]. First‐principles density functional theory (DFT) calculations are used to support the experimental findings. [ABSTRACT FROM AUTHOR]

We extend further the theoretical and experimental studies of the actual surface anchoring potential restoration by polarization microscope technique in a wedge-shaped cell with weak surface anchoring forces filled by a chiral nematic liquid crystal (in Grandjean-Cano Wedge). To realize the theoretically predicted options of observation of large director deviation angles from the easy axes the experimental studies of director distribution in Grandjean-Cano zones were performed for differing easy axes orientations at the wedge surfaces. A weak surface anchoring at one wedge surface was obtained by a photo-alignment technique. A strong surface anchoring at the second wedge surface was also obtained by a photo-alignment technique with an enlarged irradiation dose. There were observed walls with weak jumps of the director orientation between first neighboring Grandjean-Cano zones. Some experimentally obtained polarization microscope images demonstrate partially unwound director structures in zero Grandjean-Cano zone. To ensure optimal parameters of the further experiments on the actual surface anchoring potential restoration theoretical calculations of the director distribution in individual Grandjean-Cano zones were performed for various model surface anchoring potentials. It was found that especially promising for description of the experimentally found director distribution is the D-potential. As a result of the present studies the angular range of a model-independent actual azimuthal surface anchoring potential restoration was enlarge (up to π/3) and the ways of an actual surface anchoring potential restoration in a whole angular range of its determination are discussed. [ABSTRACT FROM AUTHOR]

The motion of helium crystals has been experimentally studied when the crystals fall in the superfluid liquid owing to gravity at temperatures above the roughening transitions where the whole crystal surface is in the atomically rough state. The rate of crystal fall at T = 1.25 K is higher than at T = 1.54 K. This is proof of the essential role of the normal component of superfluid helium in the deceleration of crystal motion. The pressure measurements in the container have shown the effect of surface kinetics on the motions of the crystal and its size. The fall of crystals with the low surface mobility at T = 1.54 K does not change the pressure significantly. The high surface mobility at T = 1.25 K results in decreasing the pressure in the container in the course of the fall of a crystal. The pressure drop exceeds the difference in the hydrostatic pressure between the initial and final positions of the crystal. After the stop, the pressure in the container relaxes to the difference mentioned above. This fact demonstrates an additional growth of the crystal in the flow of a superfluid liquid. [ABSTRACT FROM AUTHOR]

Liquid crystals with molecules constrained to the tangent bundle of a curved surface show interesting phenomena resulting from the tight coupling of the elastic and bulk-free energies of the liquid crystal with geometric properties of the surface. We derive a thermodynamically consistent Landau-de Gennes-Helfrich model which considers the simultaneous relaxation of the Q-tensor field and the surface. The resulting system of tensor-valued surface partial differential equation and geometric evolution laws is numerically solved to tackle the rich dynamics of this system and to compute the resulting equilibrium shape. The results strongly depend on the intrinsic and extrinsic curvature contributions and lead to unexpected asymmetric shapes. [ABSTRACT FROM AUTHOR]

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Two‐dimensional molecular crystals (2DMCs) open a new door for the controllable growth of 2D materials by molecular design with a energy gap and solution processability. However, the growth of 2DMCs with defined molecular layers remains full of challenges. Herein, we report a novel method to produce various 2DMCs with a defined number of molecular layers. When the surface tension and viscosity are tuned to control the spreading of the solution on the liquid surface, large‐area quasi‐freestanding 2DMCs from bulk size down to the monolayer limit are obtained, which makes it possible to probe the intrinsic layer‐dependent optoelectronic properties of organic semiconductors down to the physical limit, and paves the way for the application of 2DMCs in new optoelectronic devices and technologies. [ABSTRACT FROM AUTHOR]

Observer-invariance is regarded as a minimum requirement for an appropriate definition of time derivatives. We systematically discuss such time derivatives for surface tensor field and provide explicit formulations for material, upper-convected, lower-convected and Jaumann/corotational time derivatives which all lead to different physical implications. We compare these results with the corresponding time derivatives for tangential tensor fields. As specific surface 2-tensor fields we consider surface Q-tensor fields and conforming surface Q-tensor fields and apply the results in surface Landau-de Gennes models for surface liquid crystals. [ABSTRACT FROM AUTHOR]

In this paper, a dynamic plasmonic subtractive color filter is investigated. The proposed filter consists of aluminum disks immersed in nematic liquid crystal. The performance of the structure is based on the interaction between liquid crystal and localized surface plasmons, which the transmittance colors are electrically controlled by the applied voltage. The optical efficiency and the full-width at half-maximum (FWHM) of the filter are attained to be about 80 percent and 40–45 nm, respectively. Moreover, the suggested color filter is polarization-insensitive due to its symmetric geometry. [ABSTRACT FROM AUTHOR]

We extend further the theoretical and experimental studies of the actual surface anchoring potential restoration by polarisation microscope technique and using micro-images in a wedge-shaped cell with weak surface anchoring forces filled by a chiral nematic liquid crystal (in Grandjean–Cano (GC) Wedge). To realize the theoretically predicted options of observation of large director deviation angles from the easy axes, the experimental studies of director distribution in GC zones were performed for differing easy axes orientations at the wedge surfaces in white light. A weak surface anchoring at one wedge surface was obtained by a photo-alignment technique. A strong surface anchoring at the second wedge surface was obtained by a rubbing. There were observed for the first time jump-less walls (without jumps of the director orientation) between neighbouring GC zones and jumps in colour in the Newton's rings (lines) at the positions of the walls between GC zones. Qualitative explanations of the both phenomena are presented and an expression for the jump in colour value in the Newton's rings (lines) at the positions of the walls between GC zones is presented. Some experimentally found by the polarisation microscope and by the microphoto technique images demonstrate jump-less walls between the first GC zones. To ensure optimal parameters of the further experiments on the actual surface anchoring potential restoration, theoretical calculations of the director distribution in individual GC zones were performed for various model surface anchoring potentials. It was found that especially promising for description of the experimentally found director distribution looks the modified D-potential. As a result of the present studies, the ways to enlarge (compared to the previous studies) angular range of the actual surface anchoring potential restoration were proposed. [ABSTRACT FROM AUTHOR]

We analyze Ginzburg–Landau minimization problems in two dimensions with either a "strong or weak" tangential boundary condition. These problems are motivated by experiments in liquid crystals with boundary defects. The imposition of classical boundary conditions on a liquid crystal surface is referred to as "strong anchoring", while "weak anchoring" refers to the inclusion of boundary energy terms. In the singular limit when the correlation length tends to zero, we show that boundary defects will be observed for weak anchoring, while both boundary and interior vortices are possible for strong anchoring. [ABSTRACT FROM AUTHOR]

The effect of different orientations of the optic axis (OA) in the liquid crystal (LC) UCF-1 in two dimensions on the surface plasmon (SP) mode excited along the surface intermediate between a thin silver film and the LC at different temperatures is theoretically studied using the prism coupling technique and a TM-polarized, monochromatic laser with λ = 5890 Å. The shifts in the surface plasmon resonance (SPR) dip angle at different temperatures for varying alignments of the OA in a plane are determined. Changes in the SPR resonance angles with temperature are found to be significant and linear in a major part of the entire anisotropic phase of UCF-1 for the homeotropic orientation. A linear fit is obtained for the variation of SPR angle of resonance with the molecular order parameter over the entire anisotropic range of UCF-1. The effect of deviations of the OA of the LC from the homeotropic orientation in two dimensions on the temperature sensitivity of the SPR angle of resonance in the linear response temperature range is studied, and its influence on the accuracy of measurement by SPR corresponding to a fixed value of the molecular order parameter is investigated. • Linear fits for calculated SPR angles with temperature and order parameter S in anisotropic range of homeotropic UCF-1. • Calculated change in S is 0.089 for 1° change in SPR resonance angle and calculated change in SPR angle is 0.140°/K. • OA rotationsup to 10° from homeotropic perpendicular to LC-Ag interface cause slight changes in temperature sensitivity. • For OA rotation angles greater than 30°, temperature sensitivity as well as sensitivity to S decreases drastically. • Misalignment of OA from homeotropic by 1° causes error of 0.02 K in temperature measurement. [ABSTRACT FROM AUTHOR]

Crystal growth occurs at the interface of a crystal and its growth medium. Due to the abrupt termination at the surface, at the interface the properties of the crystal will typically deviate from the bulk and this can affect the growth behaviour. Also the properties of the growth medium at the interface will typically differ from the bulk. In growth from solution, for example, the liquid will show ordering induced by the crystal surface or have a different composition. Here techniques to study such growth interfaces will be discussed together with examples of the effect that the properties of the interface can have on the growth. [ABSTRACT FROM AUTHOR]

Poly(D, l -lactide) (PDLLA) as a kind of bone repair material has been widely concerned, however, the development of PDLLA material with remarkable cell affinity and osteogenic activity is still a big challenge. Inspired by the unique liquid crystal property and viscoelasticity of bone extracellular matrix (ECM), here, a new kind of chitin whisker gel (nCG) with the bone ECM-like liquid crystal phase and viscoelasticity was developed, which was further stably adhered to PDLLA membrane to obtain the nCG-coated composite membrane (PP@nCG) taking advantage of polydopamine. The design of bone ECM-like liquid crystal gel surface on the PDLLA membrane could not only improve cell adhesion and proliferation, but also highly enhance calcium phosphate mineralization. Creatively, the modulus of surface coated nCG can be easily adjusted by changing the degree of deacetylation of chitin whiskers to simulate the viscoelasticity of bone ECM and regulate cell behaviors and fate. Interestingly, the PP@nCG membrane with high-modulus nCG coating shows a stronger effect on promoting cell affinity and osteogenic activity compared with that with low-modulus nCG coating. This study opens a new window to bionic designing novel composite materials with bone ECM-like liquid crystal characteristic and viscoelasticity for bone repair. [Display omitted] [ABSTRACT FROM AUTHOR]

• Uniform alignment of liquid crystals on the PEVA surface was achieved by ion beam irradiation. • Physicochemical characteristics of PEVA surface was investigated by AFM and XPS analysis. • Ion beam induced significant chemical modification on the surface for uniform LC alignment. • IB irradiated PEVA film is a promising alternative for stable and remarkable LC alignment layers. The post-processing of a poly(ethylene-co-vinyl acetate) (PEVA) film by ion-beam (IB) irradiation is described herein for use as a liquid crystal (LC) alignment layer. Various film curing temperatures are investigated in order to achieve a stable film prior to IB irradiation, and a uniform and homogeneous LC alignment with superior optical transparency is obtained at a curing temperature of 130 °C. The chemical and morphological effects of IB irradiation are further examined by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Although the surface morphology exhibits a random pattern, the IB irradiation is found to modify the chemical characteristics of the PEVA surface by simultaneously inducing van der Waals forces and strong dipole-dipole interactions with the LCs, thus leading to unidirectional LC alignment. In addition, LC cells are fabricated from the IB-irradiated PEVA films, and the LC alignment state is confirmed by polarized optical microscopy and pre-tilt angle measurements. Further, the high transparency of the deposited PEVA film compared to that of ITO-coated glass is demonstrated via transmittance measurement. In view of this superior performance, the IB-irradiated PEVA film is a promising alternative for advanced LC displays. [ABSTRACT FROM AUTHOR]

Liquid crystals (LCs) are considered attractive lubricating materials due to their controllable molecular alignment and rheological behavior using an external electric field or a surface-alignment layer. In this study, a 1,3-diketone EPND (1-(4-ethyl phenyl) nonane-1,3-dione) fluid was tribologically investigated as an additive in a nematic liquid crystal 5CB (4-pentyl-4′-cyanobiphenyl) on steel surfaces. It shows that the chemically bonded EPND monolayer can reduce the surface energy of steel to a value lower than the surface tension of 5CB. According to the FCK rule, the EPND monolayer promotes a homeotropic alignment of 5CB, which facilitates its boundary lubrication witnessed by a Stribeck behavior test. Concerning on the influence of surface roughness change during long-term friction, it suggests that severe wear and deep grooves should be avoided by applying 5CB/EPND hybrid fluid at a low initial contact pressure (~137 MPa). In this situation the surface energy effect of EPND monolayer can dominate the molecular alignment of 5CB in the presence of shear, and lead to an ultralow coefficient of friction (= 0.008). This study shows that EPND is a promising additive for nematic liquid crystal lubricants, especially in applications with low load and high requirement for low friction. • Reduced surface energy of steel substrate chemically bonded by EPND. • Homeotropic anchoring alignment of 5CB promoted by EPND monolayer. • Ultralow friction (COF = 0.008) of 5CB induced by EPND additive. [ABSTRACT FROM AUTHOR]

• Building a LC-based sensing platform with enzyme-responsive supramolecular materials. • It has high sensitivity and specificity in detection of organophosphates. • Detection of organophosphates is achieved in lake water and orange juice. Here, we demonstrate use of acetylcholinesterase (AChE)-responsive polyoxometalate (POM)/surfactant supramolecular spheres to build a liquid crystal (LC)-based sensing platform for detection of organophosphorus pesticides. The self-assembled spheres are composed of hybrid materials of a POM, sodium dodecatungstophosphate (PW 12), and a surfactant, myristoylcholine (Myr). It displays dark appearance when the aqueous solution is in contact with LCs supported on the octadecyltrichlorosilane-treated glass deposited with the supramolecular spheres, suggesting perpendicular orientation of LCs at the aqueous/LC interface. In contrast, LCs show bright appearance when the surface-deposited supramolecular spheres are enzymatically hydrolyzed by AChE, corresponding to planar orientation of LCs at the aqueous/LC interface. Detection of organophosphates are successfully achieved as they are potent inhibitors of AChE. The detection limit of the sensing platform reached 0.9 ng/mL for dimethoate. This method can avoid disturbance of external interference with excellent specificity and sensitivity, which makes it very promise in detection of organophosphorus pesticides. [ABSTRACT FROM AUTHOR]

Biological plywoods are multifunctional fibrous composites materials, ubiquitous in nature. The chiral fibrous organization is found in chitin (insects), cellulosics (plants), and collagen I (cornea and bone of mammals) and is a solid analog of that of cholesteric liquid crystals. The surface and interfaces of plywoods are distinguished by hierarchical topographies and nanowrinkling. In this paper, we present a theory to model the emergence of these surfaces and interfaces using liquid crystal-based shape equations that directly connect material properties with geometric wrinkling. The model applies to liquid crystal precursors of the plywood solid analoges. We focus on wrinkling geometry, wrinkling mechanics, and the mechanogeometry relationships that underlie multifunctionality ubiquitous in biological surfaces. Scaling wrinkling laws that connect mechanical pressures and stresses to folding and bending are formulated and quantified. A synthesis of the connections between mechanics and geometry is achieved using the topology of stress curves and curvature of the wrinkles. Taken together the results show that anchoring is a versatile surface morphing mechanism with a rich surface bending stress field, two ingredients behind many potential multifunctionalities. [ABSTRACT FROM AUTHOR]

Herein, a method is proposed to determine the azimuthal anchoring energies of surface liquid crystals (LCs), as they gradually change orientation from a vertical to a horizontal state owing to an increase in the voltage applied to each LC cell. The LC cells are characterized using the direction of the Williams roll pattern related to the midplane LC director of the conduction regime of the electrohydrodynamic convection patterns of LCs. The application of the midplane LC directions, obtained from the direction of the roll patterns, to the Ericksen-Leslie equation produces the precise values of the surface anchoring strength. The hybrid type 90°-twisted nematic LC cell, composed of homeotropic and homogeneous LC alignment layers on the top and bottom substrates, respectively, was used to find the azimuthal anchoring energy of the surface LCs, indicated by voltages at the initially vertically aligned LC state. It was observed that the surface azimuthal anchoring energy on the homeotropic layer increased with an increase in voltage. We expect that the proposed technique may be excellent in terms of ease of use, simplicity, and accuracy because the azimuthal anchoring energy can be visually evaluated through the roll pattern. [ABSTRACT FROM AUTHOR]

Molten barium hydroxide (BHO) with strong alkalinity will absorb CO 2 in the air and denaturing part of BHO, so it is very important to treat it with liquid seal. In this paper, the effects of liquid seals with different cooling methods and white suspended substances on the phase change process of BHO were compared for phase change experiments, so as to study the influencing factors of powdery expansion of BHO and the crystal crystallization mode. The experimental results show that the probability of powdery expansion of BHO increases with the decrease of cooling rate. Liquid paraffin and high temperature silicone oil can play the role of air insulation, but will make BHO supercooling and powder expansion probability increase, some white powder suspended between molten BHO and liquid sealing material (BaCO 3 attached to tiny bubbles) has a certain promoting effect on nucleating crystallization of BHO, and the supercooling degree of BHO without white powder will increase again, the surface of the BHO crystal shows a tight structure around the loose and porous center, known as a branch cavity structure, which becomes apparent as the cooling rate increases. This experiment provides a reference for the study of phase change materials in the field of phase change energy storage. • The cause and influencing factors of powdered expansion of BHO were discovered. • The effect of liquid seal on the phase transformation process of barium hydroxide octahydrate was discovered. • The crystallization mode and macroscopic crystal structure of barium hydroxide octahydrate were discovered. [ABSTRACT FROM AUTHOR]

An approach is proposed to create robust liquid crystalline polymer coatings that exhibit sensitivity and dynamic reversibility toward multiple external stimuli including UV irradiation and electrical input. This coating spontaneously alters its surface topographic texture and thickness in response to each of these signals. The corresponding deformations are induced by the photo‐/electromechanical properties and dielectric anisotropy in the liquid crystal networks through order parameter reduction and anisotropic volume expansions. The deformation proceeds fast within several seconds both for activation and for the relaxation to the initial state upon switching the trigger(s) on and off. Light and electric field can be applied independently to excite the topographies or in a synergistic manner to enhance the deformation amplitude. Upon elimination of the combined light and electric actuating trigger, the relaxation to the initial close to flat state follows a complex pathway. Depending on the elimination order the topographic structure can be rapidly erased or can be kept in a bistable state. The results of this study are relevant for various fields, for instance, switchable controlled friction, controlled adhesion, and release of objects and haptics where they affect human perception both in passive and dynamic manner. [ABSTRACT FROM AUTHOR]

Innenrücktitelbild: Layer-Defining Strategy to Grow Two-Dimensional Molecular Crystals on a Liquid Surface down to the Monolayer Limit (Angew. Chem. 45/2019) Keywords: Grenzflächen; Organische Elektronik; Organische Halbleiter; Organische Kristalle; Photodetektoren. [Extracted from the article]

As it is known, the Rapini-Papoular potential is suitable for description of anchoring energy between the liquid crystal and bounding surfaces in the case of small deviations of the director from the easy orientation axis. We use modified surface potential that can describe the anchoring energy at large deviations of the director more adequately. The interaction effect of a cholesteric liquid crystal with a bounding surfaces on the nature and features of cholesteric-nematic phase transitions induced by an external magnetic field is studied. We determine the conditions for existence of three different phases in a cholesteric liquid crystal layer with a finite homeotropic anchoring at the boundaries. The dependencies of the threshold fields of orientational transitions between the phases of a liquid crystal on the material parameters of the cell are calculated. Landau expansions of the total free energy of cholesteric near the transition points are constructed. We determine the tricritical values of the anisotropy parameter of the surface anchoring, which characterize the nature of transitions between the phases of a cholesteric liquid crystal. Unlabelled Image • Conditions for the existence of different orientational phases in the cholesteric layer are determined. • Finite homeotropic anchoring is described by generalized Rapini-Papoular potential. • Transition between phases can be the transition of the first or the second order. • Additional anchoring constant determines the tricritical character of the transitions. [ABSTRACT FROM AUTHOR]

Liquid crystal surfaces can undergo topographical morphing in response to external cues. These shape-shifting coatings promise a revolution in various applications, from haptic feedback in soft robotics or displays to self-cleaning solar panels. The changes in surface topography can be controlled by tailoring the molecular architecture and mechanics of the liquid crystal network. However, the nanoscopic mechanisms that drive morphological transitions remain unclear. Here, we introduce a frequency-resolved nanostrain imaging method to elucidate the emergent dynamics underlying field-induced shape-shifting. We show how surface morphing occurs in three distinct stages: (i) the molecular dipoles oscillate with the alternating field (10–100 ms), (ii) this leads to collective plasticization of the glassy network (~1 s), (iii) culminating in actuation of the topography (10–100 s). The first stage appears universal and governed by dielectric coupling. By contrast, yielding and deformation rely on a delicate balance between liquid crystal order, field properties and network viscoelasticity. Liquid crystal networks can morph their shape in response to electrical stimulus. Here the authors provide a detailed description of their deformation mechanism and introduce a method to observe the dynamic surface of liquid crystal elastomers. This could help with the development of smart materials. [ABSTRACT FROM AUTHOR]