Effects of nematic polymer liquid crystal on crystallization and structure of PET/Vectra blends

We investigate the effects of a nematic liquid crystalline polymer, Vectra A, on the structure and properties of its blends with a semicrystalline polymer, poly(ethylene terephthalate),PET. PET/Vectra blend composition ranged from 100/0 to 60/40. Real-time, in situ studies ofisothermal and non-isothermal melt crystallizations of these blends were conducted usingsimultaneous wide and small angle X-ray scattering (WAXS and SAXS), differentialscanning calorimetry (DSC), and quantitative polarizing optical microscopy. All techniquesconfirm that the addition of Vectra nematic liquid crystal delays the onset of crystallization,and affects the degree of crystallinity and structural parameters such as Bragg long period,lamellar thickness and linear stack crystallinity. SAXS results indicate that some of theVectra component penetrates into the interlamellar regions of the crystal stacks. Vectrainterrupts the entangled polymer network making it more difficult for lamellar crystals tonucleate. Slower nucleation and growth result in increased perfection of the PET crystalsgrown isothermally, but reduces the crystallization temperature of PET crystals grownnon-isothermally causing these crystals to be less perfect.     

Phase transformations in the thermotropic liquid crystal polymer: 60/40 PABA/PET

Microstructures observed in 60/40 PABA/PET co-polyester in transmitted polarized light are reported. The microstructure changes as a function of temperature. Between 190 and 340 C the optical textures are similar to those seen in small molecule liquid crystals in the smectic C modification; above 340 C the textures are typical of nematic structures. At 420 C the specimen is totally isotropic and begins to degrade. Rapid cooling to below 190 C can quench in the high temperature phases, including the isotropic one. DSC traces show endotherms identifiable with the onset of mobility at 190 C, the transition from smectic C to nematic-like textures at 340 C and the development of the isotropic phase in the range 350 to 420 C. The smectic C to nematic transition in texture is associated with the appearance of a transient microstructure, known as a myelin texture, and reported here for the first time in a liquid crystal polymer.     

光刻法制备聚合物/液晶光栅

将明胶涂覆在表面经过取向处理的带有ITO电极的玻璃基板上，以紫外灯为光源，通过光掩模法，使明胶在光场的引发下发生光化学反应，样品显影刻蚀处理后呈栅状，将液晶注入光栅盒中，形成聚合物／液晶光栅。该光栅衍射效率可利用电场调控。采用He—Ne激光器对所制样品进行测试，结果表明，所制样品的栅结构较好。避免了液晶与聚合物相分离的不完全性和栅条边缘不整齐的现象。制得的光栅其第一衍射级次的开关比为87：1，显示了较好的开关能力。     

Aligned silane-treated MWCNT/liquid crystal polymer films

We report on a method to preferentially align multiwall carbon nanotubes (MWCNTs) in a liquid crystalline matrix to form stable composite thin films. The liquid crystalline monomeric chains can be crosslinked to form acrylate bridges, thereby retaining the nanotube alignment. Further post-treatment by ozone etching of the composite films leads to an increase in bulk conductivity, leading to higher emission currents when examined under conducting scanning probe microscopy. The described methodology may facilitate device manufacture where electron emission from nanosized tips is important in the creation of new display devices.     

The morphological study of liquid crystalline copolyesters based on PET and PHB

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Influence of short-fibre reinforcement on the fracture behaviour of a bulk liquid crystal polymer

The microstructure and some mechanical properties of a liquid crystal polymer (LCP) and its short-fibre composites have been investigated. Injection moulded plates of the latter materials exhibit a layered structure well-known for many short-fibre reinforced polymer systems. A pronounced layered structure is also found in the neat LCP matrix, superimposed by a certain degree of molecular orientation. The special, microstructural character of the matrix polymer results in a high anisotropy of the mechanical properties of all materials investigated. In particular, this is found for the tensile strength, the fracture toughness and the fatigue crack propagation. The composites show nearly no improvement or even a reduction in their performance, compared to the matrix material, as far as these properties are concerned. This can, in part, be correlated to microscopic failure mechanisms detected by scanning electron microscopy of the fractured surfaces, revealing that the fibre-matrix bond strength is relatively poor.     

Confinement of an antiferroelectric liquid crystal in a polymer nanonetwork: thermal and dielectric behaviour

We report the thermal and dielectric investigations on a liquid crystal exhibiting an antiferroelectric phase and confined in a polymer network of sub-micron dimensions. Two different photo-polymerizable monomers have been employed for the purpose: one of them (HDDA) is bereft of any aromatic parts, while the other (RM82) contains aromatic as well as aliphatic units and, in fact, forms a liquid crystalline phase in its monomeric state. The polymerization, which is carried out in the presence of the liquid crystalline host, is expected to yield a nanosegregated structure for HDDA and blended structure for the RM82 case, the difference reflecting the morphologies of the networks, as evidenced by SEM images. Surprisingly, even a small concentration of the latter polymer added to the former variety has substantial influence on the morphology. The main work focusses on calorimetry and dielectric relaxation spectroscopy of the host liquid crystal confined in these nanonetworks created by the polymers, which can be considered to form virtual surfaces with a finite anchoring energy. We have investigated the in-phase and antiphase modes in the antiferroelectric phase, and the soft mode in the paraelectric phase preceding the antiferroelectric phase. The relaxation frequencies of all these modes are substantially influenced by the network, with the results showing certain surprises in cases containing both HDDA and RM82.     

液晶聚合物/聚苯胺复合材料的导电性能研究

以4,4'-二羟基-a,a'-二甲基苄连(DDBA)羟基硅油合成了系列带有磺酸基团的液晶离聚物(LCI).合成的LCI与聚苯胺原位聚合制备出系列复合材料.采用红外光谱表征了LCI和复合材料的结构;用差示扫描量热法表征了复合材料的液晶性能;交流阻抗法测量了复合材料的电导率;结果表明:掺杂后的最大电导率能达到9.0×10-5/cm.     

Effects of substrate and orientational property of liquid crystal domains on the blood compatibility of polymer/liquid crystal composite membranes

A series of polymer/cholesteryl liquid crystal (LC) composite membranes were prepared. Polyurethane and polyvinyl chloride, as a substrate, were blended with cholesteryl tetraethylene glycol carbonate to form composite membranes in an electric field under normal conditions. The blood compatibility of composite materials was identified by the dynamic blood-clotting test, haemolysis ratio measurement, platelet adhesion and SEM observation. The results showed that the content of LC, the ordered extent of LC domains embedded in composite materials and the type of substrate have greater effects on the blood compatibility of polymer/LC composite materials. When the LC domains were properly oriented, polymer/LC composite membranes had an excellent haemocompatibility, fewer platelets were adhered and spread and showed little distortion on the surface of materials.     

羟基磷灰石/液晶复合材料仿生人工骨的制备及性能

通过优化的加工条件制备了羟基磷灰石/热致液晶高分子(HA/Vectra A950)复合材料仿生人工骨, 研究了HA含量对复合材料显微结构和力学性能的影响, 分析了HA与Vectra A950共混后的力学性能以及界面结合问题。研究结果表明: 当HA与Vectra A950的质量比小于10∶100时, 复合材料呈现明显的皮芯结构, 皮层液晶微纤高度取向, HA主要分散在芯部, 其模量和强度达到或超过天然骨的力学性能; 随着HA含量的增加, 皮芯结构逐步减弱并消失, 而缺陷显著增加。当HA与Vectra A950的质量比增加到20∶100, 复合材料的力学性能、尤其是韧性显著降低, 这可能是由于HA颗粒与液晶基体之间的结合较差导致的。为保证复合材料仿生人工骨的生物活性, HA的含量应与天然骨接近。因此, 需对HA和Vectra A950的界面进行改性以提高其结合性能。      

纳米氧化锌掺杂液晶/聚合物膜的阻抗谱特性

本文研究了采用纳米氧化锌棒掺杂的聚合物分散液晶(PDLC)的电阻抗谱特性及其传感应用。利用聚合物分散液晶薄膜具有稳固结构、能抵御机械冲击、容易制备等特点,在材料中掺杂纳米氧化锌棒,通过电阻抗谱性质分析,实现对极性分子如乙醇气体的传感功能。通过对比实验,研究分析了薄膜在遇到乙醇分子时的复阻抗谱的变化,并建立了电化学等效电路,发现该薄膜能有效地实现对乙醇分子的传感功能。并进一步分析研究了该检测传感的灵敏度和响应时间等特性。结果表明,以纳米氧化锌棒掺杂PDLC薄膜有望作为检测乙醇等极性的气体传感器,具有高灵敏度、结构稳定、重复性高、易于制造等优点。     

Electrically switchable holographic liquid crystal/polymer Fresnel lens using a Michelson interferometer

A holographic technique for fabricating an electrically switchable liquid crystal/polymer composite Fresnel lens is reported. A Michelson interferometer is used to produce the required Fresnel pattern, by placing a convex lens into one path of the interferometer. Simplicity of the method and the possibility of fabricating different focal length lenses in a single arrangement are advantages of the method. The performance of the fabricated lens was demonstrated and its electro-optical properties were investigated for its primary focal length.     

交流电场促进相分离法制备聚合物分散液晶

在单体与液晶相分离的过程以及单体固化的过程中施加交流电，得到液晶微滴尺寸和排列规则的PDLC膜。采用偏振红外光谱法对电场作用下液晶分子的重新取向进行了研究。结果表明：非工作状态下，液晶微滴的分子光轴处于无序态；工作状态下，分子光轴能够达到较高的有向度。     

Effects of polymer viscosity on the polymerization switching and electro-optical properties of unaligned liquid crystal/UV curable polymer composites

Polymer dispersed ferroelectric liquid crystal composite films consisting of varying polymer viscosities were prepared by polymerization induced phase separation (PIPS) technique. It was found that polymer viscosity influences the polarization switching and optical responses. A polymer dispersed ferroelectric liquid crystal film of low polymer viscosity shows faster switching, however a higher optical transmission at ~ 70% was observed in a higher polymer viscosity film.     

Measurement and analysis of the fracture of a liquid crystal polymer

The fracture initiation behaviour of injection-moulded plaques of a liquid-crystal polymer is described. Attention is restricted to cracks in the plane of the plaques propagating along the mould fill direction. The material is both anisotropic and inhomogeneous; the latter factor is accommodated by adopting a skin-core model of the plaque structure. The inhomogeneity leads to mixed mode (Modes I and II) fracture in some cases, and both single and mixedmode testing is used. The results can be represented in terms of either stress intensity or strain energy release rate by simple mixed-mode failure criteria.     

Plasma pre-treatment of liquid crystal polymer and subsequent metallization by PVD

In this paper surface modification of a liquid crystal polymer (LCP) substrate by oxygen containing plasma pre-treatment and subsequent Cu/Cr deposition by physical vapour deposition (PVD) technique is described. By pre-treatment with oxygen containing plasma more volatile reaction products are generated compared to argon plasma pre-treatment as is shown by the etching rate. The small molecule fragments generated during the pre-treatment process are analyzed by mass spectrometry. After the pre-treatment metal layers with suitable adhesion strength even after 1000 cycles of thermal shock are obtained.     

聚合物网络稳定液晶光栅的制备与特性研究

将光敏预聚物单体与向列相液晶按一定比例混合,注入液晶盒;采用光掩模法,在紫外灯照射下,使混合物产生定域光聚合反应,形成聚合物网络稳定液晶光栅。利用光学显微镜和He-Ne激光器进行测试,实验检测结果表明,该光栅具有周期性的栅结构,且衍射效率具有先增大后减小电场调制特性,并利用折射率调制机理对该现象进行分析。     

Magnetic-field-assisted formation of alignment polymer coatings in liquid crystal cells

We describe a new method for obtaining liquid crystal (LC) layers with planar orientation in plane-parallel cells, which is based on the technology of LC-polymer interface formation in solution under the action of an applied magnetic field. The azimuthal anchoring energy of LC at the polymer surface has been determined by measuring the angle of orientation of the nematic LC director on the substrate surface as a function of the magnetic field. The LC orientation provided by the proposed method is stable, and the anisotropy of LC anchoring is comparable with that achieved using well-known methods of alignment polymer film preparation by rubbing.