Fabrication of a Superhydrophobic Surface from a Smectic Liquid‐Crystal Defect Array

A novel fabrication method is developed for the preparation of superhydrophobic surfaces. The procedure uses focal conic structures of semi‐fluorinated smectic liquid crystals (LCs) whose periodic toric focal conic domains (TFCDs) are prepared on a surface modified substrate. Reactive ion etching (RIE) on the periodic TFCD surface leads to a superhydrophobic surface with a water contact angle of ～160° and a sliding angle of ～2° for a 10 µL water droplet. The results show that this phenomenon is due to the development of a dual‐scale surface roughness arising from the nanoscale protuberance caused by applying the RIE process to the top of the microscale TFCD arrays. The unique surface behavior is further verified by demonstrating that RIE on a flat lamellar liquid crystal film, in which the director is aligned parallel with surface, results in a relatively low hydrophobicity as compared to when periodic TFCDs are subjected to REI. The observations made in this publication suggest that a new approach exists for selecting potential candidates of superhydrophic surface formation based on spontaneous self‐assembly in smectic liquid‐crystalline materials.     

Controlling the Self‐Assembly of Periodic Defect Patterns in Smectic Liquid Crystal Films with Electric Fields

Large‐area periodic defect patterns are produced in smectic A liquid crystals confined between rigid plate electrodes that impose conflicting parallel and normal anchoring conditions, inducing the formation of topological defects. Highly oriented stripe patterns are created in samples thinner than 2 μm due to self‐assembly of linear defect domains with period smaller than 4 μm, whereas hexagonal lattices of focal conic domains appear for thicker samples. The pattern type (1d/2d) and period can be controlled at the nematic–smectic phase transition by applying an electric field, which confines the defect domains to a thin surface layer with thickness comparable to the nematic coherence length. The pattern morphology persists in the smectic phase even after varying the field or switching it off. Bistable, non‐equilibrium patterns are stabilized by topological constraints of the smectic phase that hinder the rearrangement of defects in response to field variations.     

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.     

Nematic Anisotropic Liquid‐Crystal Gels—Self‐Assembled Nanocomposites with High Electromechanical Response

The uniqueness of liquid crystals (LCs) lies in the large anisotropies of their properties, which can be utilized to generate high electromechanical responses. In a properly oriented LC polymer system, an external electric field can induce reorientation of the mesogenic units possessing a dielectric anisotropy, which, when coupled with the shape anisotropy of the mesogenic units, can in turn produce large mechanical strain. Anisotropic LC gels, which can be obtained by in‐situ photopolymerization of the reactive LC molecules in the presence of non‐reactive LC molecules in an oriented state, are an example of such liquid‐crystal polymer systems. It is shown here that a homeotropically aligned LC gel in its nematic phase exhibits high electrically induced strain (> 2 %) with an elastic modulus of 100 MPa and a high electromechanical conversion efficiency (75 %) under an electric field of 25 MV/m. These anisotropic LC polymeric materials could provide a technologically compatible system for such applications as artificial muscles and as microelectromechanical devices.     

柱状腔向列相液晶指向矢结构的Monte Carlo模拟

液晶分子被限定在柱状腔内,基于Gruhn-Hess两体势,通过Monte Carlo模拟方法,研究了径向边界条件及温度对柱状腔内向列相液晶PAA的指向矢结构的影响。文中计算了系统平衡后的二阶序参数、轴向序参数、径向序参数、角向序参数和指向矢快照图。在自由表面条件下,液晶分子在与柱轴垂直的面内呈均匀一致排列,而径向锚定作用下,指向矢结构为平面极性结构;在径向锚定作用下,随着锚定强度的增加,液晶分子在与柱状腔轴垂直的面内径向排列有序度增加;温度的变化会改变液晶分子的有序度,但不改变其指向矢结构。     

Sub‐5 nm Dendrimer Directed Self‐Assembly with Large‐Area Uniform Alignment by Graphoepitaxy

Directed self‐assembly (DSA) using soft materials is an important method for producing periodic nanostructures because it is a simple, cost‐effective process for fabricating high‐resolution patterns. Most of the previously reported DSA methods exploit the self‐assembly of block copolymers, which generates a wide range of nanostructures. In this study, cylinders obtained from supramolecular dendrimer films with a high resolution (<5 nm) exhibit planar ordering over a macroscopic area via guiding topographical templates with a high aspect ratio (>10) and high spatial resolution (≈20 nm) of guiding line patterns. Theoretical and experimental studies reveal that this property is related to geometrical anchoring on the meniscus region and physical surface anchoring on the sidewall. Furthermore, this DSA of dendrimer cylinders is demonstrated by the non‐regular geometry of the patterned template. The macroscopic planar alignment of the dendrimer nanostructure reveals an extremely small feature size (≈4.7 nm) on the wafer scale (>16 cm²). This study is expected to open avenues for the production of a large family of supramolecular dendrimers with different phases and feature dimensions oriented by the DSA approach.     

Alignment of liquid crystals on a topographically nano-patterned polymer surface prepared by a soft-imprint technique

In this study, we have fabricated polyacrylate substrates having a nano-patterned surface topography using a soft-imprint technique. The planar alignment of liquid crystals (LCs) along the direction of nanogrooves has been generated. Twisting behavior of nematic LCs has been also observed with a perpendicularly assembled LC cell and the cell parameters can be estimated by using the Soutar and Lu method. By comparing the anchoring energies obtained, accordingly, it has been demonstrated that the polymer nanogroove pattern has a comparable influence on LC alignment to the conventional rubbing process. It has been also shown that the artificial topography of the line grooves on the conventionally rubbed surface has a significant influence on the anchoring stability of the LC molecules.     

Biopolymer Templated Glass with a Twist: Controlling the Chirality,Porosity, and Photonic Properties of Silica with Cellulose Nanocrystals

A detailed investigation of the formation and properties of mesoporous silica templated by the chiral nematic liquid crystal phase of cellulose nanocrystals (CNCs) is presented. Under appropriate conditions, CNCs co‐assemble with silica up to loadings of ≈60 wt% to give composite films with periodic chiral nanostructures. The periodicity of these films can be readily controlled to obtain materials that selectively reflect light with wavelengths ranging from ≈400–1400 nm. The co‐assembly of CNCs and silica into ordered chiral nematic structures is demonstrated to occur within a narrow window of pH and is affected by aging: a slow rate of silica condensation appears to be vital for the formation of well‐ordered materials. CNCs can be removed from the composite films by calcination or acid hydrolysis to give high surface area chiral nematic mesoporous silica (CNMS) with tunable pore diameters. The combination of mesoporosity and chiral nematic ordering in CNMS enables it to be used in a unique way for refractometric sensing applications. It is shown that, when using circular dichroism (CD) signals to monitor the chiral photonic properties of CNMS, variations in refractive index can be detected based on changes of both CD signal intensity and peak position with good sensitivity.     

栅状表面液晶盒的光学特性

栅状表面基板对液晶分子有特殊的锚定作用,其锚定的强度和易取方向与栅状表面的几何参数相关。两块预先处理的栅状表面基板可以制成液晶显示器件,其光学特性也与栅状表面的几何参数相关。文中基于Frank弹性理论和栅状表面基板的等效锚定能公式研究了外加电压下此种液晶盒的光学特性,并通过计算机模拟得到了不同栅状表面液晶盒的电光曲线,且与栅状表面液晶盒的闽值电压进行了比较。     

“Brick‐and‐Mortar” Self‐Assembly Approach to Graphitic Mesoporous Carbon Nanocomposites

Mesoporous carbon materials do not have sufficient ordering at the atomic scale to exhibit good electronic conductivity. To date, mesoporous carbons having uniform mesopores and high surface areas have been prepared from partially‐graphitizable precursors in the presence of templates. High temperature thermal treatments above 2000 °C, which are usually required to increase conductivity, result in a partial or total collapse of the mesoporous structures and reduced surface areas induced by growth of graphitic domains, limiting their applications in electric double layer capacitors and lithium‐ion batteries. In this work, we successfully implemented a “brick‐and‐mortar” approach to obtain ordered graphitic mesoporous carbon nanocomposites with tunable mesopore sizes below 850 °C without using graphitization catalysts or high temperature thermal treatments. Phenolic resin‐based mesoporous carbons act as mortar to highly conductive carbon blacks and carbon onions (bricks). The capacitance and resistivity of final materials can be tailored by changing the mortar to brick ratios.     

Enhanced and Engineered d0 Ferromagnetism in Molecularly‐Thin Zinc Oxide Nanosheets

Molecularly‐thin nanosheets are ultimate two‐dimensional (2D) nanomaterials potentially giving unusual physical and chemical properties due to the strong 2D quantum and surface effects. Here, it is demonstrated that 1.5‐nm‐thick ZnO nanosheets exhibit greatly enhanced room‐temperature ferromagnetism. Saturation magnetization value of the nanosheets with intercalated dodecyl sulfate layers is approximately 100 times that of ZnO mesocrystals. Anion exchange with dodecyl phosphate layers strongly suppresses ferromagnetic ordering as a result of surface defect passivation while maintaining bulk‐like n‐type semiconducting properties, which reveals significance of interfacial states to engineer functional properties of nanosheet‐based hybrid materials.     

光控取向弱锚定表面的液晶分子排列

研究了光敏聚酰亚胺ＰＩ（ＢＴＤＡ－ＴＭＭＤＡ）用于液晶取向时的弱锚定边界特性。实验测得了两基板皆为摩擦取向层扭曲向列液晶显示器件（ＤＲ－ＴＮ－ＬＣＤ）及两基板皆为光控取向层的扭曲向列液晶显示器件（ＤＬＰＰ－ＴＮ－ＬＣＤ）的电光特性和时间响应特性曲线。研究了液晶排列的稳定性,讨论了液晶分子在光控取向弱锚定表面上的排列机理。     

纳米结构表面向列相液晶的聚合物锚定效应

提出了纳米结构聚合物表面的一个简化模型:由具有交替的沿面和垂面锚定的一维周期性条纹表面表征。利用Alexe-Ionescu等提出的扩展各向异性表面能形式,研究了向列相和取向层聚合物之间的锚定以及聚合物和基板表面之间的锚定对向列相液晶表面锚定的影响。在理论处理中,假设两不同锚定区域的锚定强度相等。结果表明:聚合物和基板表面之间的锚定会影响向列相的指向矢分布,降低松弛距离以及系统的总自由能。     

取向层参数对响应时间的影响

为了减小液晶波前校正器的响应时间,本文结合光控取向技术,研究了取向层预倾角及锚定强度特性对器件响应性能的影响。以液晶动力学方程为依据,分析预倾角效应对液晶器件响应时间的影响;利用预倾角及锚定强度与响应时间的定量关系,推导出锚定强度与预倾角的关系,从而简化了锚定强度的测量方法。采用光谱法监测了光控取向膜的取向度;以此为依据,利用4种不同曝光方式获得了不同的预倾角。理论模拟及实验结果一致表明:偶氮染料分子(SD1)获得一定的锚定强度后,通过降低其预倾角角度,其所制器件的响应性能实现了优化。     

Morphology of Polymer/Liquid‐Crystal Nanotubes: Influence of Confinement

Polymer/liquid‐crystal (LC) tubes consisting of an approximately 30 nm thick poly(methyl methacrylate) (PMMA) layer on the outside and a 5 to 10 nm thick discotic liquid‐crystalline layer on the inside of the tube walls have been prepared by wetting ordered porous alumina templates with a pore diameter of 400 nm. Decreasing the pore diameter to 60 nm results in a confinement‐induced transition from a wetting state to a non‐wetting state, and solid rods with a sequential morphology are obtained. The texture of the mesophase depends on the morphology type and the thermal history. Under certain conditions the LC mesophase exhibits a dominant, well‐ordered planar texture where the discotic columns are aligned with the long axes of the tubes. The controlled generation of one‐dimensional nano‐objects possessing mesoscopic fine structures and intrinsic anisotropy should be the first step towards a rational design of miniaturized building blocks.     

Flexible bistable cholesteric reflective displays

Cholesteric liquid crystals (ChLCs) exhibit two stable states at zero field condition - the reflecting planar state and the nonreflecting focal conic state. ChLCs are an excellent candidate for inexpensive and rugged electronic books and papers. This paper will review the display cell structure, materials and drive schemes for flexible bistable cholesteric (Ch) reflective displays.     

基板表面锚泊对液晶全漏导模影响的理论研究

平行排列向列相液晶盒基板表面锚泊能可以影响液晶盒内液晶分子指向矢的分布,光学上将导致液晶导模结构的变化。为了研究基板表面锚泊对液晶全漏导模的影响,首先基于液晶弹性理论推导了液晶指向矢在外加电压下满足的平衡态方程,随后由差分迭代方法数值计算液晶指向矢。最后,基于液晶多层光学理论推导了液晶导波反射率和透射率公式,并通过数值计算得到了平行排列向列相液晶全漏波导反射率Rss随内角变化的理论曲线。计算结果表明,相对于强锚泊情形(1×10~(-3) J/m~2),不同锚泊能强度(5×10~(-5) J/m~2～1×10~(-3) J/m~2)下的理论曲线会发生左移现象,移动距离与锚泊能强度有关。由曲线移动的距离可以确定液晶盒基板表面锚泊能的强度。该研究为进一步利用光导波技术测量液晶盒基板表面锚泊能强度提供了理论依据。     

Interface Immobilization Chemistry of cRGD‐based Peptides Regulates Integrin Mediated Cell Adhesion

The interaction of specific surface receptors of the integrin family with different extracellular matrix‐based ligands is of utmost importance for the cellular adhesion process. A ligand consists of an integrin‐binding group, here cyclic RGDfX, a spacer molecule that lifts the integrin‐binding group from the surface and a surface anchoring group. c(‐RGDfX‐) peptides are bound to gold nanoparticle structured surfaces via polyproline, polyethylene glycol or aminohexanoic acid containing spacers of different lengths. Although keeping the integrin‐binding c(‐RGDfX‐) peptides constant for all compounds, changes of the ligand's spacer chemistry and length reveal significant differences in cell adhesion activation and focal adhesion formation. Polyproline‐based peptides demonstrate improved cell adhesion kinetics and focal adhesion formation compared with common aminohexanoic acid or polyethylene glycol spacers. Binding activity can additionally be improved by applying ligands with two head groups, inducing a multimeric effect. This study gives insights into spacer‐based differences in integrin‐driven cell adhesion processes and remarkably highlights the polyproline‐based spacers as suitable ligand‐presenting templates for surface functionalization.     

Bioinspired Design Criteria for Damage‐Resistant Materials with Periodically Varying Microstructure

Many biological materials, such as bone, nacre, or certain deep‐sea glass sponges, have a hierarchical structure that makes them stiff, tough, and damage tolerant. Different structural features contributing to these exceptional properties have been identified, but a common motif of these materials, the periodic arrangement of structural components with strongly varying stiffness, has not gained sufficient attention. Here we show that the periodicity of the material properties is one of the dominant reasons for the high fracture resistance of these structures and their tolerance to short cracks. If the composite architecture fulfills certain design rules, which are derived in this paper, the stiff structure becomes fracture resistant and, most of all, flaw tolerant. This architectural criterion inspired from nature provides useful guidelines for the design of defect‐tolerant resistant man‐made materials.     

混合排列柱状薄层中的向列相液晶指向矢分布的研究

利用向列相液晶弹性理论,研究了混合排列柱状薄层中的向列相液晶指向矢的分布。向列相液晶被限定在两个同心圆柱构成的薄层中,在内外表面施加强锚定及弱锚定边界条件,锚定易取向方向取径向和轴向(垂直柱轴及平行柱轴)的边界条件,得到了四种混合排列柱状薄层模型RsZw、ZwRs、RwZs、ZsRw。基于Frank弹性自由能和Rapini-Papoular近似的表面能,研究了不同锚定强度、不同内半径及不同弹性常数值的指向矢分布,计算机模拟得出指向矢取向的曲线图。由于柱对称性、锚定强度、薄层厚度以及弹性各向异性共同竞争的影响,这四种模型的指向矢分布有着很大的不同。