Melt spinning and annealing of poly(ethylene terephthalate)/p‐hydroxybenzoate liquid crystalline polymer

Poly(ethylene terephthalate)/p‐hydroxybenzoate (PET/PHB) copolymer materials have relatively low melt viscosity because of the 60 mol % PHB material having a value that is lower by approximately two orders of magnitude than the value for PET homopolymer. The structure development during melt spinning and thermal treatment (annealing) of liquid crystalline copolyesters, with a rigid backbone structure, were analyzed through the density, birefringence, X‐ray diffraction, DSC, dynamic viscoelasticity, and tensile testing. As the take‐up velocity increased, the birefringence of PET/PHB as‐spun fiber increased, which indicated that it directly influenced the initial modulus and specific stress. The lateral packing of PHB molecular chain in a copolymer was shown to be loosened in the course of thermal treatment. The thermal treatment slightly increased the crystal orientation factor, whereas total molecular orientation was decreased by annealing. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1265–1278, 2004     

未来的生活与生产环境

地点—空间的选择将会是企业战略的一部分。本文讨论宏观社会趋势 (如人口、科技、价值观、经济、工作和环境 )对未来的城市、办公、零售、居住、工业等的选点与空间设计的影响     

可读 必不用之书(一)——顺谈操守

指出美国规划理论家约翰·弗里德曼 (JohnFriedmann)的社会改革理论是种不负责任的理想主义。在中国不能用。尤其会影响规划事业和工作者的的操守。     

Structural development of poly(ethylene 2,6‐naphthalene dicarboxylate) film upon solvent drawing

To investigate the effect of “chemical energy” by solvent on structural development, initially molded amorphous poly(ethylene 2,6‐naphthalene dicarboxylate) (PEN) films were drawn in various solvent systems and at the optimum temperatures deliberately determined, and the resulting fine structure and properties were analyzed by using several experimental techniques. Water, 1‐butanol, 1,4‐dioxane/water (20 : 80 by volume), and 1,4‐dioxane/1‐butanol (20 : 80 by volume) were chosen for drawing solvent. For this study, in view of chemical structure and solubility parameter, though, these are nearly immiscible or partially miscible liquids against PEN, with just the plasticizing actions more or less the primary concern here. Interesting enough, the temperature range near the main endothermic peak corresponding to the depressed boiling point of liquid caused by unfavorable interaction between PEN and solvent in mixtures of amorphous PEN film with various solvent systems, as determined by the DSC scans, was found to coincide with the optimum drawable range for each solvent system, over which several experiments, including the determination of maximum draw ratio (DR_max) have been carried out throughout the study. The experimental results obtained from this study could be explained, through qualitatively, in terms of the interactions between PEN and solvents. Hence, it is expected to control the fine structure and properties of PEN films resulting from the low‐temperature solvent drawing via a suitable choice of liquids and the corresponding draw temperature ranges. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1357–1365, 2003     

西部地区开发战略——来自国际与加拿大开发经验的一些启示

介绍第二次世界大战后西方国家的国际开发理论 ;加拿大地区开发的政策、成果和理论启示 ,及其西部省份的开发情况和展望 ;借此 ,针对中国西部地区开发和城市化问题 ,提出了自己的看法。     

比较研究:论方法

引进外国的规划手段应先做比较研究。我们要先认识外国手段与外国背景的关系 ,才可以适当地修正引用到中国。本文讨论西方比较研究的方法 ,并提出一个“背景迁移”分析法     

Perovskite‐Based Phototransistors and Hybrid Photodetectors

In the past several years, organic–inorganic hybrid perovskites and all inorganic perovskites have attracted enormous research interest in a variety of optoelectronic applications including solar cells, light‐emitting diodes, semiconductor lasers, and photodetectors for their plenty of appealing electrical and optoelectrical properties. Benefiting from the inherent amplification function of transistors and the pronounced photogating effect, perovskite‐based phototransistors and hybrid photodetectors can provide very high photoresponsivity and gain, rendering them highly promising for some specific applications especially ultrasensitive light detection. A review on the recent progress of phototransistors and hybrid photodetectors using perovskites as light‐sensitive materials is presented. The efforts and development in 3D and 2D perovskite‐based phototransistors, and perovskite/functional material (e.g., graphene, 2D semiconductors, organic semiconductors, and other semiconductors) heterojunction‐based hybrid photodetectors are introduced and discussed systematically. Some processing techniques for optimizing device performance are also addressed. In the final section, a conclusion of the research achievements is presented and possible challenges as well as outlook are provided to guide future activity in this research field.     

Autonomously Responsive Membranes for Chemical Warfare Protection

Stimuli‐responsive materials offer new opportunities to resolve long‐standing material challenges and are rapidly gaining pivotal roles in diverse applications. For example, smart protective garments that rapidly transport water vapor and autonomously block chemical threats are expected to enable an effective new paradigm of adaptive personal protection. However, the incorporation of these seemingly incompatible properties into a single responsive system remains elusive. Herein, a bistable membrane that can rapidly, selectively, and reversibly transition from a highly breathable state in a safe environment to a chemically protective state when exposed to organophosphate threats such as sarin is demonstrated. Dynamic response to chemical stimuli is achieved through the physical collapse of an ultrathin copolymer layer on the membrane surface, which efficiently gates transport through membrane pores composed of single‐walled carbon nanotubes (SWNTs). The adoption of nanometer‐wide SWNTs for ultrafast moisture conduction enables a simultaneous boost in size‐sieving selectivity and water‐vapor permeability by decreasing nanotube diameter, thereby overcoming the breathability/protection trade‐off that limits conventional membrane materials. Adaptive multifunctional membranes based on this platform greatly extend the active use of a protective garment and present exciting opportunities in many other areas including separation processes, sensing, and smart delivery.     

Novel CO2 laser drawing of thermotropic liquid crystal polymer and poly(ethylene 2,6‐naphthalate) blend fibers

Thermotropic liquid crystal polymer (TLCP)/poly(ethylene 2,6‐naphthalate) (PEN) were prepared by a melt blending, and were melt spun by a spin‐draw process. In this study, we suggest novel drawing technology using the CO₂ laser that can directly and uniformly heat up fiber inside to prevent the formation of ununiform structures in conventional heat drawing process. The properties of the heat/laser drawn TLCP/PEN blend fibers were superior to those of any other handled fibers, and were rather more excellent than those of TLCP/PEN blend fibers annealed at 135°C for 10 min. It was confirmed that the CO₂ laser drawing made it possible to achieve the optimal drawing effect by draw ratio. The combined heating and CO₂ laser‐drawing method has a great potential for industrial applications as a novel fiber‐drawing process, and it can also be applied continuously to conventional spin‐draw system. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 205–211, 2007     

Optimization of diffusion-weighted single-refocused spin-echo EPI by reducing eddy-current artifacts and shortening the echo time

Objective

The purpose of this work was to optimize the acquisition of diffusion-weighted (DW) single-refocused spin-echo (srSE) data without intrinsic eddy-current compensation (ECC) for an improved performance of ECC postprocessing. The rationale is that srSE sequences without ECC may yield shorter echo times (TE) and thus higher signal-to-noise ratios (SNR) than srSE or twice-refocused spin-echo (trSE) schemes with intrinsic ECC.

Materials and methods

The proposed method employs dummy scans with DW gradients to drive eddy currents into a steady state before data acquisition. Parameters of the ECC postprocessing algorithm were also optimized. Simulations were performed to obtain minimum TE values for the proposed sequence and sequences with intrinsic ECC. Experimentally, the proposed method was compared with standard DW-trSE imaging, both in vitro and in vivo.

Results

Simulations showed substantially shorter TE for the proposed method than for methods with intrinsic ECC when using shortened echo readouts. Data of the proposed method showed a marked increase in SNR. A dummy scan duration of at least 1.5 s improved performance of the ECC postprocessing algorithm.

Conclusion

Changes proposed for the DW-srSE sequence and for the parameter setting of the postprocessing ECC algorithm considerably reduced eddy-current artifacts and provided a higher SNR.