Electric‐Field‐Controlled Alignment of Rod‐Shaped Fluorescent Nanocrystals in Smectic Liquid Crystal Defect Arrays

Periodic micro‐arrays of straight linear defects containing nanoparticles can be created over large surface areas at the transition from the nematic to smectic‐A phase in a nanoparticle–liquid crystal (LC) composite material confined under the effect of conflicting anchoring conditions (unidirectional planar vs normal) and electric fields. Anisomeric dichroic dye molecules and rod‐shaped fluorescent semiconductor nanocrystals (dot‐in‐rods) with large permanent electric dipole and high linearly polarized photoluminescence quantum yield align parallel to the local LC molecular director and follow its reorientation under application of the electric field. In the nano‐sized core regions of linear defects, where the director is undefined, anisotropic particles align parallel to the defect whereas spherical quantum dots do not show any particular interaction with the defect. Under application of an electric field, ferroelectric semiconductor nanoparticles in the core region align along the field, perpendicular to the defect direction, whereas dichroic dyes remain parallel to the defect. This study provides useful insights into the complex interaction of anisotropic nanoparticles and anisotropic soft materials such as LCs in the presence of external fields, which may help the development of field‐responsive nanoparticle‐based functional materials.     

一种新型液晶垂直取向膜

采用离子沉积法在玻璃基板表面制备了十四烷基磺酸盐自组装膜,用带有该自组装膜的基板制成的液晶器件呈现出垂直取向效果。通过自组装反应过程分析,认为自组装膜表面的纵向沟纹引起了液晶的垂直排列。实验发现,当自组装膜烷烃碳链长度大于11个C原子就可获得垂直取向。这种取向膜制作过程简单、热稳定性好,非常有望应用于多畴垂直取向模式的液晶显示器。     

Self‐Assembly in Hopper‐Shaped Crystals

Hopper shape is a special type of crystal morphology. Hopper‐shaped crystals possess unique properties and show promise in many different applications. The understanding of how the building blocks (atoms, ions, and molecules) assemble into hopper‐shaped crystals and how the environmental factors influence the assembly process is critical to the properties and applications of hopper‐shaped crystals. In this review, the important interfacial instability theories that outline the underlying mechanisms for the formation of hopper‐shaped crystals are discussed. Next, the relevant experimental developments based on three categories of synthetic approaches are discussed: the growth through the control of the solute concentration, the temperature gradient, and the capping agent. At the end of the review, the applications, opportunities, and potential challenges of the hopper‐shaped crystals are discussed.     

Light‐Driven Electrohydrodynamic Instabilities in Liquid Crystals

The induction of electrohydrodynamic instabilities in nematic liquid crystals through light illumination are reported. For this purpose, a photochromic spiropyran is added to the liquid crystal mixture. When an electrical field is applied in the absence of UV light, the homeotropic liquid crystal reorients perpendicular to the electrical field driven by its negative dielectric anisotropy. Upon exposure to UV light, the nonionic spiropyran isomerizes to the zwitterionic merocyanine form inducing electrohydrodynamic instabilities which turns the cell from transparent into highly scattering. The reverse isomerization to closed‐ring spiropyran form occurs thermally or under visible light, which stops the electrohydrodynamic instabilities and the cell becomes transparent again. It is demonstrated that the photoionic electrohydrodynamic instabilities can be used for light regulation. Local exposure, either to drive the electrohydrodynamics or to remove them enables the formation of colored images.     

激光诱导液晶定向研究

报道了一种新的激光诱导液晶定向技术。用偏振激光辐照两块涂有聚乙烯醇（ＰＶＡ）和甲基橙（ＭＯ）混合物薄膜的玻璃基片,再按激发光偏振态相互垂直的方向组装为液晶（ＬＣ）盒,用光诱导法获得盒内液晶分子的扭曲向列排列,该盒可使入射线偏振光旋转９０°。用１ＧＷ／ｃｍ２强激光辐照后,盒内ＬＣ分子取向不变,因而可望用于制备强激光系统中偏光控制器以改善光束质量。     

Highly Oriented Nanofibrils of Regioregular Poly(3‐hexylthiophene) Formed via Block Copolymer Self‐Assembly in Liquid Crystals

A novel method making use of block copolymer self‐assembly in nematic liquid crystals (LCs) is described for preparing macroscopically oriented nanofibrils of π‐conjugated semiconducting polymers. Upon cooling, a diblock copolymer composed of regioregular poly(3‐hexylthiophene) (P3HT) and a liquid crystalline polymer (LCP) in a block‐selective LC solvent can self‐assemble into oriented nanofibrils exhibiting highly anisotropic absorption and polarized photoluminescence emission. An unusual feature of the nanofibrils is that P3HT chains are oriented along the fibrils' long axis. This general method makes it possible to use LCs as an anisotropic medium to grow oriented nanofibrils of many semiconducting polymers insoluble in LCs.     

Controlled Planar Alignment of Discotic Liquid Crystals in Microchannels Made Using SU8 Photoresist

A range of triphenylene and phthalocyanine‐based discotic liquid crystals (DLCs) can be aligned within micrometer‐scale channels formed from SU8 patterned on silicon or glass surfaces. The channels can be filled with the DLC in its isotropic phase using capillary action. Alignment occurs spontaneously as the sample is slowly cooled into the Col_h phase. Whilst all of these DLCs align with the columns perpendicular to the surface when they are ‘sandwiched’ between glass slides, in these channels, the DLC aligns with the column director parallel to the surface. It is also constrained to lie across the channels. The same alignment occurs when these DLCs are confined between SU8‐topped interdigitated gold electrodes where it gives the optimum orientation for electrode‐to‐electrode conduction. The quality of the alignment depends on the particular liquid crystal used and on the width of the channel. For the Col_r phase of octaoctylphthalocyanine there is additional epitaxial control over the orientation of the lattice such that the a/c face of the lattice is parallel to the surface. This is an important prerequisite for creating a bistable display device that switches by virtue of changing the direction of the tilt of the discs.     

Self‐Powered Optical Switch Based on Triboelectrification‐Triggered Liquid Crystal Alignment for Wireless Sensing

Here, a self‐powered optical switch (OS) composed of a surface‐etched single‐electrode triboelectric nanogenerator (TENG) and a polymer‐dispersed liquid crystal (PDLC) film is reported. The working principle of the developed OS is that the liquid crystal alignment can be driven by triboelectrification‐generated voltage, inducing the PDLC film to rapidly switch its initial translucent state to an instantaneous transparent state. An output voltage of 360 V is generated upon the PDLC film when a nitrile rubber film contacts with the TENG at an area of 25 cm² and a velocity of 0.4 m s^?1. As such, a wide dimming range with the relative transmitted light intensity from 0.05 to 0.85 can be achieved for the OS. Enabled by the unique mechano‐electro‐optical reaction, the effects of a series of structural parameters on the performance of the OS are methodically studied. Particularly, through integrating the OS with a visible‐light‐operated signal‐processing circuit, a complete wireless sensing system with a fully power‐free sensing node is developed. The paradigms of hand touching and foot stepping triggered wireless alarms are demonstrated, explicitly showing great potential for the system in many possible interactive human–machine interface applications, such as surveillance, security systems, remote operation, and automatic control.     

Large Area Self‐Assembly of Nematic Liquid‐Crystal‐Functionalized Gold Nanorods

Fascinating nematic‐ and smectic‐like self‐assembled arrays are observed for gold nanorods partially capped with either laterally or terminally attached nematic liquid crystals upon slow evaporation of an organic solvent on TEM grids. These arrays can be manipulated and reoriented by applying an external magnetic field from quasi‐planar to vertical similar to a Fréedericksz transition of common organic nematic liquid crystals. Birefringence and thin film textures of these self‐assembled gold nanorod arrays observed by polarized optical microscopy are strongly reminiscent of common organic nematic liquid crystal textures between crossed polarizers and, additionally, support the formation of ordered liquid crystal‐like anisotropic superstructures. The ordering within these arrays is also confirmed in bulk samples using small angle X‐ray scattering (SAXS).     

侧链含稠环的新型聚酰亚胺液晶垂直取向剂的制备及表征

以3,5-二硝基苯甲酰氯、雌二醇及溴代正辛烷为原料合成了含有稠环结构的新型功能性二胺(H8-c)。用1,2,3,4-环丁烷四甲酸二酐(CBDA)、对苯二胺(PDA)及H8-c共聚制备了一种聚酰亚胺(PI)液晶垂直取向剂。该PI膜作为取向层制得的液晶盒,在120℃下烘烤12h仍可垂直取向,拥有良好的垂直取向热稳定性。热重分析(TGA)测试表明其具有良好的热稳定性,在氮气中,这种PI的5%热失重温度(T5)和10%热失重温度(T10)分别高达400℃和480℃。紫外可见光谱(UV-vis)显示此PI膜在400nm以上具有高的透过率,可达95%以上。     

Self‐Aligned Single‐Crystal Graphene Grains

The precisely controllable growth of self‐aligned single‐crystal graphene grains on liquid Cu surface by ambient pressure chemical vapor deposition is reported. Large scale monolayer graphene arrays are modulated by varying growth conditions such as flow rate of carbon source, growth temperature, and growth time. Further, bilayer graphene grains are also controllably prepared under optimized growth conditions. The self‐alignment mechanism of graphene is also studied and a growth model is proposed to explain that process involving surface tension of liquid phase. In all, the growth mechanism of graphene arrays is firstly probed and the grown graphene arrays show reasonable mobility and high current density, posing great potential for graphene‐based electronics.     

Magnetic Tilting in Nematic Liquid Crystals Driven by Self-Assembly

Self-assembly is one of the crucial mechanisms allowing the design multifunctional materials. Soft hybrid materials contain components of different natures and exhibit competitive interactions which drive self-organization into structures of a particular function. Here a novel type of a magnetic hybrid material where the molecular tilt can be manipulated through a delicate balance between the topologically-assisted colloidal self-assembly of magnetic nanoparticles and the anisotropic molecular interactions in a liquid crystal matrix is demonstrated.     

胆甾相液晶双轴特性的计算

采用自洽模拟方法计算了胆甾相液晶双轴序参数随温度和分子手征作用强度的变化,并与实验进行了比较。结果表明,双轴特性与液晶物质和温度有关,但主要产生于胆甾相液晶的螺旋结构、分子的手征特性和取向的有序性     

Size‐Selective Binding of Sodium and Potassium Ions in Nanoporous Thin Films of Polymerized Liquid Crystals

The development of a nanoporous material from a columnar liquid crystalline complex between a polymerizable benzoic acid derivative and a 1,3,5‐tris(1H‐benzo[d]imidazol‐2‐yl)benzene template molecule is described. The morphology of the liquid crystalline complex is retained upon polymerization and quantitative removal of the template molecule affords a nanoporous material with the same lattice parameters. The nanoporous material selectively binds cations from aqueous solution, with selectivity for sodium and potassium ions over lithium and barium ions, as shown with FT‐IR. Binding is also quantified gravimetrically with a quartz crystal microbalance with dissipation monitoring, a technique that is used for this purpose for the first time here.     

π‐Conjugated Oligothiophene‐Based Polycatenar Liquid Crystals: Self‐Organization and Photoconductive,Luminescent, and Redox Properties

A series of liquid‐crystalline (LC) π‐ ‐conjugated oligothiophenes bearing three or two alkoxy chains at their extremities has been designed and synthesized. These polycatenar oligothiophenes form various LC nanostructures including smectic, columnar, and micellar cubic phases. These properties depend on the number and length of the terminal alkoxy chains. The hole mobilities for the oligothiophenes have been measured. The layered smectic and columnar structures are capable of transporting holes, leading to mobilities of up to 0.01 cm² V^?1 s^?1. The columnar LC assemblies have also been explored to produce linearly polarized light‐emission. Fine red polarized fluorescence is observed from a uniaxially aligned film of the oligothiophenes. The redox properties of the oligothiophenes both in solutions and in films have been examined. The oligothiophenes exhibit electrochromism upon applying an oxidative potential. The present design strategy is useful for fabricating a variety of functional electro‐active molecular assemblies.     

Spontaneous Formation of Liquid Crystals in Ultralarge Graphene Oxide Dispersions

A novel process is developed to synthesize graphene oxide sheets with an ultralarge size based on a solution‐phase method involving pre‐exfoliation of graphite flakes. Spontaneous formation of lyotropic nematic liquid crystals is identified upon the addition of the ultralarge graphene oxide sheets in water above a critical concentration of about 0.1 wt%. It is the lowest filler content ever reported for the formation of liquid crystals from any colloid, arising mainly from the ultrahigh aspect ratio of the graphene oxide sheets of over 30 000. It is proposed that the self‐assembled brick‐like graphene oxide nanostructure can be applied in many areas, such as energy‐storage devices and nanocomposites with a high degree of orientation.