Applications of liquid crystal polymers

The science and technology of liquid crystal polymers is selectively reviewed with an emphasis on those aspects key to successful commercial utility. The importance of the low viscosity demonstrated by nematic polymers under commercial processing conditions, coupled with the low volume change on cooling and high thermal stability associated with these nematogens, is identified as the major factor behind the success of the thermotropic copolyester as a high-performance molding resin. The developing area of side-chain liquid crystal polymers as electro-optical media is discussed, stressing the importance of combining function and processibility for ultimate commercial viability. Potential markets and projected commercial growth rates are discussed from the point of view of the enabling science needed to successfully define and implement new commercial applications for liquid crystal polymers.     

The fluidity and molding ability of glass-forming Zr-based alloy melt

The fluidity and filling ability of glass-forming Zr-based alloy melt in copper mould were investigated both theoretically and experimentally. The major factors which affected the flowing behavior of the metallic melt in the mold were determined, which provides the foundation for overcoming the contradiction between the filling and formation of amorphous alloy during the rapid cooling process of the metallic melts. The casting factors to prepare a metallic ring were discussed and selected. As a result, a Zr-based bulk metallic glass ring was prepared successfully. Supported by the National Natural Science Foundation of China (Grant No. 50731005), SKPBRC (Grant No. 2006CB605201/2007CB616915), PCSIRT (Grant No. IRT0650), the Natural Science Foundation of Hebei Province of China (Grant No. E2004000209), the Scientific Research Foundation of Education Department of Hebei Province of China (Grant No. 2004464), and the Experts and Scholars Fund of Personnel Department of Hebei Province, China (Grant No. 2003)     

Replica symmetry breaking in the Ising spin glass model on Bethe-like lattices with loop

The Ising spin glass model on Bethe-like lattices (cactus lattices) is studied using replicas in the presence of a magnetic field. Parisi's order parameter function and the de Almeida–Thouless (AT) line are obtained close to the spin glass transition temperature. The results are compared with those for the Bethe lattice to see the effects of loops. The slope of the order parameter function diminishes considerably for both lattices compared with that for the Sherrington–Kirkpatrick (SK) model. The loci of the AT line for the cactus lattices and the Bethe lattice are above and below that for the SK model, respectively.     

Bioinspired preparation of regular dual‐level micropillars on polypropylene surfaces with robust hydrophobicity inspired by green bristlegrass leaves

The fine microstructure on the natural green bristlegrass leaf of Setaria viridis (L.) Beauv, which exhibits a contact angle (CA) of 155°±2° and a rolling angle (RA) of 79°±2°, is carefully observed. Based on the understanding of the underlying mechanisms for superhydrophobicity and moderate surface adhesion, an efficient replica molding strategy is proposed for mimicking the microstructures on green bristlegrass leaf surface to polypropylene (PP) surfaces. The bioinspired PP replica with dual‐level micropillars are molded by using the unitized template of steel Meshes A and B. Interestingly, the PP replica inherits both hydrophobicity and adhesion of the natural leaf. Furthermore, the PP replica can stabilize its hydrophobic state under a 980 Pa external pressure, which is attributed to the composite Cassie‐Wenzel mixed wetting state on the microstructured interface. The CA comparatively goes down and RA increases, resulting in superhydrophobic surface with moderate adhesion on the bioinspired surface. Hence, the microstructures and hydrophobicity are successfully replicated to the PP surface by only using the low cost, available and reliable steel meshes in the bioinspired replica molding process.     

Fabrication of PDMS microlens array by digital maskless grayscale lithography and replica molding technique

This paper presents a facile and effective method to fabricate microlens array in polydimethylsiloxane (PDMS). The microlens array model is fabricated in photoresist via digital maskless grayscale lithography technique and the replica molding technique is used to fabricate PDMS microlens array. A convex PDMS microlens array with rectangular aperture and concave PDMS microlens array with hexagonal aperture are fabricated. The morphological characteristics of the microlens arrays are measured by microscope and 3D profiler. The results indicate that the profiles of the PDMS microlens arrays are clear and distinct. This method provides a simple and low-cost approach to prepare large area, concave or convex with arbitrary shape microlens array, which has potential application in many optoelectronic devices.     

添加剂和注塑工艺对AES颜色稳定性的影响

通过透射电子显微镜(TEM)研究发现,未染色丙烯腈―三元乙丙橡胶―苯乙烯共聚物(AES树脂)的宏观颜色变化与其橡胶形态密切相关,而橡胶形态受配方中添加剂组分的影响很大。另外,注塑工艺也会影响AES注塑样品的宏观颜色变化。通过在体系中加入润滑剂硬脂酸钙或芥酸酰胺,可以有效地控制AES注塑样品的颜色变化。     

RTM用苯乙炔封端聚(甲基次乙炔基硅烷)树脂的流变特性

以可用于RTM成型的含硅炔杂化树脂体系为研究对象,深入研究了树脂体系的流变特性,并根据双阿仑尼鸟斯方程,建立了流变修正模型,该模型可揭示树脂在不同温度下的黏度行为.研究表明:恒温与动态条件下的树脂流变行为符合阿仑尼鸟斯流变模型,模型的计算结果和实验测试结果吻合得较好.     

Morphological development in water assisted injection molded polyethylene/polyamide‐6 blends

Water assisted injection molding (WAIM) has gradually become one of the most important polymer processing methods for making hollowed parts. This study examined the morphological development in water assisted injection molded high density polyethylene (HDPE)/polyamide‐6 (PA‐6) blends. Samples for microscopic observation were prepared by an 80‐ton injection‐molding machine equipped with a tube cavity and with a water injection unit. A distinct skin layer, core region, and channel layer were observed across the thickness. The shape and size of the dispersed phase depended on the position both across the part thickness and along the flow direction. Small and large particles coexisted in the skin and channel layers, indicating that both coalescence and disintegration of the dispersed phase occurred in these layers. High water pressures were found to mold parts with smaller polyamide particle distributions. Additionally, the morphology of water assisted injection molded parts was compared to that of gas assisted injection molded products. It was found that water molded parts exhibit a smaller polyamide particle distribution than their gas counterparts. Copyright © 2010 John Wiley & Sons, Ltd.