The Internal Structure of the Velvet Worm Projectile Slime: A Small-Angle Scattering Study

For prey capture and defense, velvet worms eject an adhesive slime which has been established as a model system for recyclable complex liquids. Triggered by mechanical agitation, the liquid bio-adhesive rapidly transitions into solid fibers. In order to understand this mechanoresponsive behavior, here, the nanostructural organization of slime components are studied using small-angle scattering with neutrons and X-rays. The scattering intensities are successfully described with a three-component model accounting for proteins of two dominant molecular weight fractions and nanoscale globules. In contrast to the previous assumption that high molecular weight proteins—the presumed building blocks of the fiber core—are contained in the nanoglobules, it is found that the majority of slime proteins exist freely in solution. Only less than 10% of the slime proteins are contained in the nanoglobules, necessitating a reassessment of their function in fiber formation. Comparing scattering data of slime re-hydrated with light and heavy water reveals that the majority of lipids in slime are contained in the nanoglobules with homogeneous distribution. Vibrating mechanical impact under exclusion of air neither leads to formation of fibers nor alters the bulk structure of slime significantly, suggesting that interfacial phenomena and directional shearing are required for fiber formation.     

Langmuir Blodgett films of arachidic acid and a nematic liquid crystal: Characterization and use in homeotropic alignment

We study the behavior of a mixed Langmuir monolayer consisting of a fatty acid and a nematic liquid crystal. We demonstrate that the mixed monolayer successfully transfers as a Langmuir-Blodgett film and characterize the transferred film using UV spectroscopy. An important application of Langmuir-Blodgett films is in the alignment of liquid crystals for electro-optical applications, such as displays. We show that including the liquid crystal in the Langmuir-Blodgett film produces homeotropic alignment for a system which fails to align by other standard techniques.     

3D Microstructures of Liquid Crystal Networks with Programmed Voxelated Director Fields

The shape-shifting behavior of liquid crystal networks (LCNs) and elastomers (LCEs) is a result of an interplay between their initial geometrical shape and their molecular alignment. For years, reliance on either one-step in situ or two-step film processing techniques has limited the shape-change transformations from 2D to 3D geometries. The combination of various fabrication techniques, alignment methods, and chemical formulations developed in recent years has introduced new opportunities to achieve 3D-to-3D shape-transformations in large scales, albeit the precise control of local molecular alignment in microscale 3D constructs remains a challenge. Here, the voxel-by-voxel encoding of nematic alignment in 3D microstructures of LCNs produced by two-photon polymerization using high-resolution topographical features is demonstrated. 3D LCN microstructures (suspended films, coils, and rings) with designable 2D and 3D director fields with a resolution of 5 µm are achieved. Different shape transformations of LCN microstructures with the same geometry but dissimilar molecular alignments upon actuation are elicited. This strategy offers higher freedom in the shape-change programming of 3D LCN microstructures and expands their applicability in emerging technologies, such as small-scale soft robots and devices and responsive surfaces.     

端羧基分散剂对PS/纳米CaCO_3复合材料性能的影响

以巯基乙酸为链转移剂制备了不同分子量的含端羧基聚丙烯酸丁酯(PBACOOH)低聚物分散剂,并将其用于聚苯乙烯(PS)/纳米CaCO3复合材料的分散改性。通过动态流变仪、电子拉力机及差示扫描量热仪对复合材料性能进行表征。结果表明,PBACOOH可提高PS/纳米CaCO3复合材料的拉伸强度及缺口冲击强度,缺口冲击强度的增幅最高可达54%。含量为纳米粒子用量1%(质量分数)的PBACOOH分散剂使复合材料熔体储能模量、损耗模量及黏度下降,G′与G″的交点频率向高频方向移动。随分子量降低及端羧基含量增加,物理老化试样在Tg转变区的解缠结热焓增大。     

溶致液晶聚芳酰胺自组装单分子膜的摩擦学性能

研究了制膜溶液相态的不同对溶致液晶聚芳酰胺(PPTA)分子沉积膜摩擦学性能的影响,分析了PPTA分子沉积膜向对偶面的转移与沉积,并讨论了转移膜性能与PPTA优良的抗磨减摩性能之间的关系。结果表明,PPTA转移膜与对偶面之间具有一定的结合力,摩擦过程实际上是在沉积膜与转移膜之间进行。当对偶面上的转移膜脱落时,PPTA的沉积膜的摩擦系数逐渐增大并且很快被磨穿。     

超高分子量聚丙烯腈在碳纤维原丝上的应用及拉伸行为研究进展

超高分子量聚丙烯腈(UHMWPAN)由于结晶度高、分子链结构规整、端基少,成纤后的缺陷也少,因此在制备高强度聚丙烯腈原丝以及高强度碳纤维方面有着重要的应用。文中介绍了用高相对分子质量(340万占3%,34万占97%的)的聚丙烯腈树脂进行溶液纺丝并制备碳纤维原丝以及碳纤维的工艺,并重点介绍了超高分子量聚丙烯腈凝胶膜的拉伸性能、超高分子量聚丙烯腈溶液的流变性能等。流变学研究表明,随着PAN相对分子质量的增大,纺丝液的黏度也会剧增,造成溶液的纺丝过程变得愈加困难。提高UHMWPAN纺丝液的温度,能有效减低溶液纺丝时的阻力。因此,开发UHMWPAN高温纺丝技术可能是未来高强度碳纤维原丝的发展方向。     

Self-assembled liquid-crystalline gels designed from the bottom up

Liquid crystals are often combined with polymers to influence the liquid crystals' orientation and mechanical properties, but at the expense of reorientation speed or uniformity of alignment. We introduce a new method to create self-assembled nematic liquid-crystal gels using an ABA triblock copolymer with a side-group liquid-crystalline midblock and liquid-crystal-phobic endblocks. In contrast to in situ polymerized networks, these physical gels are homogeneous systems with a solubilized polymer network giving them exceptional optical uniformity and well-defined crosslink density. Furthermore, the unusually high-molecular-weight polymers used allow gels to form at lower concentrations than previously accessible. This enables these gels to be aligned by surface anchoring, shear, or magnetic fields. The high content of small-molecule liquid crystal (>/=95%) allows access to a regime of fast reorientation dynamics.     

The preparation of high quality y-type polyimide Langmuir-Blodgett films

This paper describes a method which we have developed to prepare high quality polyimide Langmuir-Blodgett films. The key was to achieve good Y-type deposition of the polyamic acid Langmuir films from which the polyimide films are derived. It was found to be important to control two factors carefully: the time between preparation of the spreading solution and its use, and the pressure- annealing time of the Langmuir film. The characterization of the films, which involved liquid crystal alignment properties, Fourier transform IR, scanning electron microscopy, and scanning tunneling microscopy, showed that the structural integrity was much higher for the Y-type films. Also the degree of polymer chain alignment within each layer was again much higher for the Y-type films.     

近晶C(S_C)相串型液晶高分子的合成与表征(Ⅱ)

以含液晶基元的单体 2 ,5-二 (对异烷氧基苯甲酰氧基 ) -对苯二酚和不同结构的脂族二酰氯 ,采用低温溶液缩聚的方法 ,合成了一系列新的液晶基元垂直于分子主链的 SC相串型液晶高分子。单体的结构通过元素分析、IR、1H-NMR和 MS等方法确证。聚合物通过 GPC、DSC、TG、WAXD和偏光显微镜等方法测试表征。研究发现 ,所有的聚合物加热至各自的熔点以上都能形成液晶态 ,在液晶态可以观察到破焦锥织构 ,通过变温 X射线衍射证明它们为 SC相。所有聚合物的熔点和液晶态的清亮点随分子中末端烷氧基增大和柔性间隔段长度增加逐渐降低 ,液晶态温度范围变窄。     

液晶摩擦学研究现状与展望

综述了近年来国内外液晶摩擦学的研究进展。比较了不同小分子液晶润滑剂或添加剂的润滑机理和减摩抗磨性能的差异；总结和分析了大分子液晶微观和宏观增强复合材料的摩擦磨损机理和性能；并对液晶摩擦学今后的研究和发展方向提出了展望。     

双峰分布聚乙烯的动态流变行为

以六种不同分子量分布特征的聚乙烯为研究对象,通过动态流变、高压毛细管流变以及凝胶渗透色谱(GFC)等分析测试手段,对这六种聚乙烯的结构和性能进行对比分析.高压毛细管的结果表明,A样品表现出更好加工稳定性和更宽的加工速率窗口,结合该样品的分子量及分子量分布特别是动态流变行为,笔者认为,样品中高低分子量部分的微相分布状态对...     

Surface alignment of liquid crystal multilayers evaporated on photoaligned polyimide film observed by surface profiler

The investigation of the surface alignment of liquid crystal (LC) multilayers evaporated on photoaligned polyimide vertical alignment (PI-VA) film was carried out by means of the novel three-dimensional (3D) surface profiler. We report the first use of the surface profiler to visualize a microscopic image of the monolayer arrangement of LC molecules in contact with the surface of photo-treated PI-VA film. The photoinduced anisotropy of partially UV-exposed PI-VA film can be visualized as a topological image of LC multilayers. It seems that the topology of LC multilayers is indicating the orientational distribution of LC molecules on the treated film. It was found that the periodically photoaligned PI-VA film surface can align an adsorbed LC monolayer and the LC molecular alignment can be extended to the bulk via the epitaxylike LC–LC interaction, i.e. a short-range molecular interaction. With regard to the unexposed PI-VA film surface, noticeable anisotropy in the monolayer alignment was not observed, indicating that the long-range elastic interaction may be responsible for the bulk alignment. The appearance of small droplets in the masked region may be presumably related to the dewetting phenomena.     

Surface alignment of liquid crystal multilayers evaporated on photoaligned polyimide film observed by surface profiler

The investigation of the surface alignment of liquid crystal (LC) multilayers evaporated on photoaligned polyimide vertical alignment (PI-VA) film was carried out by means of the novel three-dimensional (3D) surface profiler. We report the first use of the surface profiler to visualize a microscopic image of the monolayer arrangement of LC molecules in contact with the surface of photo-treated PI-VA film. The photoinduced anisotropy of partially UV-exposed PI-VA film can be visualized as a topological image of LC multilayers. It seems that the topology of LC multilayers is indicating the orientational distribution of LC molecules on the treated film. It was found that the periodically photoaligned PI-VA film surface can align an adsorbed LC monolayer and the LC molecular alignment can be extended to the bulk via the epitaxylike LC–LC interaction, i.e. a short-range molecular interaction. With regard to the unexposed PI-VA film surface, noticeable anisotropy in the monolayer alignment was not observed, indicating that the long-range elastic interaction may be responsible for the bulk alignment. The appearance of small droplets in the masked region may be presumably related to the dewetting phenomena.     

四臂星型尼龙6的合成与表征

以2,2,6,6-四丙酸环己酮为四官能团核心,进行己内酰胺的水解开环聚合,合成了四种不同臂长的四臂星型尼龙6,对产物的分子量进行了测定,并对其力学性能和流变行为进行了研究。结果表明,四臂星型尼龙6的分子量随着四丙酸环己酮含量的提高而降低,与相应分子量的线型尼龙6相比,星型尼龙6的拉伸强度和弯曲强度基本保持,冲击强度保持率在75%以上,断裂伸长率最大降低了15%,相对黏度降低了近25%,熔融指数提高了近4倍,平衡转矩降低了75%,表现出了较好的加工流动性。     

Anisotropy and Raman absorption of the polyimide surface irradiated by the ion beam for liquid crystal alignment

In this paper, polyimide surfaces irradiated by an ion-beam for liquid crystal alignment are investigated by using atomic force microscopy, Raman spectroscopy, and spectroscopic ellipsometry. A liquid crystal cell aligned homogeneously through the ion-beam exposure exhibits electro-optic switching behavior similar to that of a rubbing-aligned liquid crystal cell. However, we found that the surface morphology and bonding molecules of ion-beam-treated polyimide surfaces show properties very different from mechanically-rubbed ones. Experimental results show that optical anisotropy of ion-beam-treated polyimide surfaces results in the formation of hydrogenated amorphous carbon-like structure with a short main-chain, while mechanical rubbing has little effect on structural and compositional variations of polyimide layers.     

液晶垂直取向膜材料的研究

叙述了近几年来液晶垂直取向材料领域的发展。对目前常见的几种具有应用前景的垂直取向技术分别给予了关注,同时初步探讨了其各自的取向机理,并展望了该技术在未来几年可能获得的发展。     

UP／GF／TLCP混杂复合材料的流变性能与力学性能

采用自行合成的不同相对分子质量(n)的热致性液晶聚合物(TLCP)与玻璃纤维(GF)混杂改性不饱和聚酯(UP),固定TLCP用量为5%(质量分数),研究了UP/GF/TLCP复合材料的流变性能和力学性能,分析了材料的冲击断面微观形貌。结果表明,TLCP的相对分子质量(n)对复合材料流变性能和力学性能有很大影响,当n不大于10时,复合材料的流变性能和力学性能随n的增加而提高。当n=10时,复合材料的流动性能和弯曲性能最好,熔体流动速率达到164.1 g/(10 min)。常温下弯曲强度和弯曲模量达到82.88 MPa和6.03 GPa,分别提高了31.3%和30.8%。当n=50时,复合材料的冲击强度最佳,达到5.196 kJ/m2,是未加TLCP材料的1.62倍,冲击断面形貌表明,TLCP相对分子质量对复合材料的界面粘合作用影响显著。     

Effect of the shape of imprinted alignment layer on the molecular orientation of liquid crystal

The molecular alignment of liquid crystals was studied with three different imprinted patterns. The three different shapes of molds (square-, V- and U-shaped) replicated the microstructures with electroplating process was fabricated. Surfaces with three different microgrooved patterns were used as the alignment layer of the liquid crystal cell. The effect of the shape of imprinted alignment layer on the molecular orientation of LC was investigated. Among these patterns, U-shaped groove pattern resulted in a high performance of liquid crystal orientation, pretilt angle and anchoring energy, which are quite comparable to the conventionally rubbed layer. It clearly shows that the molecular orientation of liquid crystals is influenced by the shape of microgrooved patterns.     

Improvement in device performance from a mixture of a liquid crystal and photosensitive acrylic prepolymer with the photoinduced vertical alignment method

In a multicomponent nematic liquid crystal (NLC) mixture of a liquid crystal (negative-type NLC) and a photosensitive acrylic prepolymer, photopolymerization upon UV irradiation induces the separation of the LC and photosensitive acrylic prepolymer layers, thereby leading to a vertical arrangement of LC molecules. In this study, we propose a simple vertical alignment method for LC molecules, by adding a chiral smectic A (SmA∗) liquid crystal having homeotropic texture characteristics to an NLC mixture solution. Measurements of electro-optical properties revealed that the addition of the SmA∗ LC not only strengthened the anchoring force of the copolymer alignment film surface, but also significantly enhanced the contrast ratio (∼73%), response time and grayscale switching performance of the device.     

Polyimide photo-alignment layers for inclined homeotropic alignment of liquid crystal molecules

We have succeeded in realizing an inclined homeotropic alignment of liquid crystal (LC) molecules by using photo-aligned films of a polyimide containing azobenzene in the backbone structure. To induce such an LC alignment, a side chain structure was introduced into the backbone structure. The LC pretilt angle, measured from the surface normal, could be controlled up to 1.75° by varying the light exposure in oblique angle irradiation with unpolarized light. Its thermal stability was examined by annealing the LC cell at 100 °C. No change was observed in the pretilt angle even after annealing for 36 h, indicative of its excellent thermal stability. Since photo-alignment has patterning capability, the photo-aligned polyimide film is expected as a promising alignment film for multi-domain vertical alignment mode LC displays.