Microstructured Nematic Liquid Crystalline Elastomer Surfaces with Switchable Wetting Properties

Inspired by the lotus leaf, scientists have developed many superhydrophobic surfaces, some of which show remarkable switching between hydrophobic and hydrophilic state under external stimuli. However, the switch usually relies on the change of chemical properties rather than on the modification of the topographic structure of the surface. In this paper, the roughness‐change‐related switchable wetting properties of microstructured responsive surfaces made of nematic liquid crystalline elastomers (LCEs) is reported. First, various carbonate LC monomers and side‐on LCEs are synthesized with low nematic‐to‐isotropic transition temperature, T_NI. Then, LCEs prepared from 3″‐vinylcarbonyloxypropyl 2,5‐di(4′‐octyloxybenzoyloxy)benzoate monomer, with T_NI of 76 °C and contraction of 34% are used to construct a surface covered with micropillar arrays by using a replica molding technique. The contraction of the micropillars induces a reversible roughness change of the microstructured surface. Water contact angle of this microstructured surface changed with temperature, indicating a successful approach at building a surface with switchable wetting properties.     

Molecular Engineering of Mesogenic Constituents Within Liquid Crystalline Elastomers to Sharpen Thermotropic Actuation

Liquid crystalline elastomers (LCE) are stimuli-responsive materials with a distinguished mechanical response. LCE have been subject to numerous recent functional examinations in robotics, health sciences, and optics. The liquid crystallinity of the elastomeric polymer networks of LCE are largely derived from liquid crystalline monomer precursors. Recent reports have utilized commercially available liquid crystalline diacrylate monomers in chain extension reactions to prepare LCE. These reactions have been largely based on monomeric precursors originally to enhance the and thermal stability of optical films. Here, it is demonstrated that preparing LCE via a liquid crystalline diacrylate with reduced mesogen–mesogen interaction enhances and sharpens the thermotropic actuation of these materials. Robust composition-response correlations are demonstrated in LCE prepared by three common synthetic methods. The enhanced thermotropic response of LCE prepared from this precursor increases the thermomechanical efficiency by sixfold. Accordingly, this work addresses important limitations in utilizing the thermal response of LCE in robotics, health care, and consumer goods.     

近晶A球粒织构聚硅氧烷侧链液晶的合成与液晶性能研究

以小分子蓝相小板块液晶(反,反)-4-丙基-4′-乙烯基双环己烷(3HHV)为液晶基元,通过与聚甲基氢硅氧烷进行硅氢加成反应,合成了一种新的聚硅氧烷侧链液晶,产率为78%。通过傅立叶变换红外光谱(FT-IR)和核磁共振谱(1 H-NMR)对单体和聚合物进行结构表征,证实了单体中双环己烷结构和双键的存在,说明了硅氢加成反应近于完全;通过热失重分析仪(TGA)分析了单体和聚合物的耐热性;通过差示扫描量热仪(DSC)、热台偏光显微镜(POM)和X射线衍射仪(XRD)对单体和聚合物的液晶行为进行分析,证实了二者液晶性的存在,且聚合物的介晶区间相比于单体提高了98.4℃,同时POM分析还揭示了合成的液晶高分子在降温过程中呈现出的罕有的聚合物近晶A球粒织构。     

Microstructured Photopolymerization of Liquid Crystalline Elastomers in Oxygen‐Rich Environments

Liquid crystal elastomers (LCEs) are soft materials that undergo large anisotropic shape change in response to stimuli. Rational organization of the local director field can impart spatial control of the strain profile, enabling stretch‐based deformation capable of nearly 20 J kg^?1 of output force. LCEs are increasingly being considered in end‐use applications in robotics, therapeutics, and optics. Here, a new synthetic approach is introduced to prepare LCEs composed of main chain mesogens via the cationic photopolymerization of the epoxy liquid crystal monomer (LCM). This examination details the optical, mechanical, and thermal properties of epoxide‐based LCEs as a function of spacer length (3, 6, or 11 carbons). The oxygen insensitivity of the cationic photopolymerization of these monomers makes this approach particularly attractive for implementation with emerging additive manufacturing techniques. This contribution focuses on microstructuring LCEs via 2‐photon direct laser writing (2P‐DLW). A custom heated cell facilitated 2P‐DLW of the aligned LCE epoxy resin melts to fabricate diverse geometric arrays. Enabled by the orthogonality of the reaction chemistry, hybrid and microstructured material compositions are prepared via the encapsulation of LCE epoxy micropatterns with free‐radical polymerization of acrylate‐based LCEs. The distinct thermomechanical response of the hybridized and microstructured LCE composites enables local and spatially controlled actuation.     

一种丙烯酸酯型侧链液晶高分子的合成及液晶性的研究

依据液晶分子结构理论,选择联苯基作为介晶基元,六亚甲基为柔性间隔基,合成了一种丙烯酸酯侧链型液晶高分子。对于合成的中间及目标产物通过FTIR、1HNMR等进行了结构的表征。对于聚合物采用GPC法测量了其分子量,并通过DSC、POM、XRD和计算机模拟等手段研究了其液晶性。研究表明合成的聚合物分子量-Mn=2523、-Mw=2826,具有较宽的温域(45.3～95.2℃),且为典型的近晶A相液晶。     

Mechano-Optical Sensors Fabricated with Multilayered Liquid Crystal Elastomers Exhibiting Tunable Deformation Recovery

Advances in tuning the mechanoresponsive behavior of liquid crystal elastomers have facilitated the development of next-generation applications such as reconfigurable photonic/electronic materials, energy-harvesting devices, and flexible sensors. However, the molecular-level control of mechanical responses remains difficult, with limited tunability achieved for recovery processes after stimulus removal. Herein, a design concept is proposed for facilely tuning the recovery of both the macroscopic deformation and molecular orientation change of liquid crystal elastomers using layered materials that exhibit the desired mechanoresponsive behavior. Changing the layering materials (a polydimethylsiloxane film with elastic response to a polymethylpenten film with plastic response) alters the relaxation time from <1 s to >6 months. To demonstrate this concept, highly sensitive, stretchable mechano-optical sensors with fast and ultraslow recovery times are developed that enable an applied strain to be quantitatively detected in real time or memorized with high spatial resolution, even with a conventional camera. This material design concept for arbitrarily controlling the recovery response can provide a platform for stimuli-responsive applications.     

弯曲型向列相液晶研究进展

弯曲型向列相液晶是近年来新发现的一类具有特殊光电性能的液晶材料。这类液晶分子具有独特的弯曲形状,表现出不同于棒状液晶的优良特性;但这些弯曲型向列相液晶分子普遍存在着熔点高,易出现宽温近晶相的问题。文章对以取代间苯二酚、萘环、噁二唑环等为中心环,酯键、碳(氮)氮双键等为桥键的弯曲型向列相液晶化合物的分子结构、特性、研究进展以及侧位取代对液晶性能的影响做了简要概述。     

高空间频率向列相液晶二进制光栅

研究了向列相液晶在空间变化电场作用下的电光特性。模拟了向列相液晶相位光栅的旨向矢分布。随着光栅空间频率的增加条纹电场变得很重要，而且衍射方式也发生了变化。分析了光栅的光学性能并进行了实际测量。     

Patterning Smectic Liquid Crystals for OFETs at Low Temperature

The preparation of regular microstructures with liquid crystalline materials for organic field effect transistors (OFETs) is an attractive but challenging issue. However, it is usually limited by the difficulty of forming large‐area single crystals aligned in a desirable direction. Herein, several terthiophene (TTP) smectic liquid crystals such as 8‐TTP‐8 and 12‐TTP‐11OH are patterned into highly crystalline microstripes by a sandwich system through a dewetting method. Morphology and orientation of the microstripes strongly depend on preparation temperature. Microstripes prepared below crystalline temperature are uniform, well‐ordered, and show high field effect transistor (FET) mobility. Meanwhile, π–π stacking direction of the TTP backbone is perpendicular to the microstripe and the molecules stack in layer structure, standing up on the SiO₂/Si substrate, which would provide an effective pathway for p‐type charge transport. However, higher preparation temperatures at liquid crystalline or isotropic liquid range induce many defects in the crystal formation process and cause incline of the unit cell, thus leading to a sharp decrease in FET mobility. A possible mechanism of molecular stacking at different temperature range is proposed. This strategy promised to provide a new opportunity for the high cost‐efficiency fabrication of OFETs.     

向列相液晶四波混频的若干问题

对向列相液晶四波混频进行了理论分析,总结了提高向列相液晶四波混频衍射效率的方法,评述了其相位共轭的研究现状和前景.     

向列相液晶在电场作用下的第一类弗雷德里克兹转变

本论文针对向列相液晶,从自由能的角度出发,分弹性形变和电场作用两个部分,在理论上分析了其在电场作用下的第一类弗雷德里克兹转变,得到了阈值电场与液晶材料物理性质之间的关系,并与磁场作用下的第一类弗雷德里克兹转变进行了比较。阈值电压的结论可用于测定液晶材料的展曲弹性系数。     

用自旋波理论研究向列相液晶

采用自旋波理论研究向列相液晶。由于液晶分子的长轴取向与分子绕长轴转动的角动量方向一致．可引人算符研究向列相液晶。通过对两分子作用势进行变换，得到系统哈密顿的表示形式与铁磁自旋波理论的哈密顿形式相同，进而得到序参数与约化温度的关系，在低温区与实验结果符合得较好．在接近于相变点的高温区，利用哈密顿求得相变点，与Maier-Saupe的结果接近。     

新型多畴扭曲向列相液晶显示器

提出在像素电极下方放置凸起物,获得具有宽视角特性的多畴扭曲向列相液晶显示器。该模式比传统的多畴TN模式摩擦过程少,工艺过程简单。在这种液晶显示器中,初始状态(未加电)时,分子排列结构和普通单畴TN模式相同,在加电压状态时,由于凸起物的存在,液晶分子沿着4个不同的方向排列形成多畴区域。文中运用专业液晶模拟软件模拟,对该液晶显示器的电光特性进行研究,结果表明,该液晶显示器具有宽视角、色散小及色彩还原性较好的特性。     

垂直排列一扭曲向列液晶显示的阈值特性

从液晶体系的总自由能出发,通过欧拉-拉格朗日方程组的推导,得到了手性向列相液晶从垂直排列状态转变成平面扭曲排列时的Freedericksz转变阈值电压公式Vth=π×     

向列相液晶中的耦合自相位调制现象

通过实验研究了C60掺杂的向列相液晶(5CB)在低光强下的自相位调制现象。样品经过二波耦合实验之后液晶分子进行一定的取向,这时在水平和竖直偏振光的照射下可观察到明显的自相位调制现象。改变入射光的偏振方向可以看到自相位调制的衍射图样也随之改变,原因就是液晶折射率变化的各向异性。可见,液晶盒中的分子取向与光束的偏振方向有很强的依赖关系。     

扭曲向列相液晶盒的制作及测试

论文介绍了一项基于高职院校实验实训平台的扭曲向列相液晶盒制作实验及其测试效果。文中详细论述了该实验的各个工艺流程,实验所用各器件及材料,各流程操作实施方法,并对实验中制作的液晶盒进行了基本特性测试。该实验在实际教学过程中使用效果较好。     

Light-Guided Dynamic Liquid Crystalline Elastomer Actuators enabled by Mussel Adhesive Protein Chemistry

Light-guided soft actuators with dynamic polymer networks have drawn much attention in recent years. However, the application of such actuators is limited by their synthetic strategies, polymer structures, and shape-morphing modes. This work reports a new class of liquid crystalline elastomer (LCE) actuators crosslinked by mussel-inspired catechol-Fe (III) complexes. The actuators are mechanically strong while being self-healable, shape-reprogrammable, and reprocessable. Importantly, the formation of catechol-Fe (III) complexes enables the single-component LCE network to exhibit outstanding photothermal effects without any light-absorbing additives. Thus, actuators with designable structures and complex shape-morphing capabilities can be readily programmed with mechanical force coupled with either environmental heating or NIR light irradiation. Furthermore, the material platform provides a robust and flexible way to fabricate actuators with different dimensional structures varying from 1D to 3D. The LCE shows great potential in robotic fields, and as a proof-of-concept, a crawling robot, C-Bot, is specially designed. The robot is capable of moving untethered both on solid-substrate and water surfaces under the guidance of light based on the mechanisms of shape-morphing and Marangoni propulsion, respectively. Surprisingly, different from the vast majority of previously reported LCE-based robots, the C-Bot is strong enough to carry a heavy load while moving.     

电场诱导向列相液晶二阶线性光学效应

本文报道向列相液晶在电场诱导下以及经液晶池界面化学处理后，获得了垂直结构的体系的位相匹配且产生了二次谐波．首次测定该液晶的非线性系数张量的矩阵各分量，并给出诱导场强与谐波强度的关系．