Self-assembly behavior of polymer-assisted clays

Layered silicate clays are natural crystallites that are well recognized for their practical uses, but little is known about their self-assembly behavior. In this review, we summarize the recent literature on clay interactions with organic polymers as well as clay self-assembly with organic involvement. We place emphasis on two aspects of these non-covalent interactions: first, plate-like clays can have a considerable impact on polymer properties such as hydrogels and clay films, and also on the encapsulation of bio-molecules. Second, through ionic intercalation with polymeric amine-salts, the clay layered structure units can be modified and enabled to self-assemble into ordered arrays such as rod-, dendrite-, and fiber-like microstructures. The silicate self-assembled morphologies such as worm-like and hollow microspheres were obtained in epoxy matrices and during spray drying, respectively. A mechanism was proposed for the clay self-assembly in two orientations, platelet face-to-face (ionic attraction) and edge-to-edge (organic hydrophobic effect). Further, the layered clays after the exfoliation into random platelets (1 nm in thickness) had strong propensity toward self-piling without any organic influence. Formation of lengthy rods or fibrils up to 5 μm in length and their hierarchical transformation under transmission electron microscope (TEM) electron beam bombardment and ultrasonication were observed. The clay thin-platelet geometric shape and surface ionic charge are two important parameters for the self-assembling tendency. The high surface of clay platelet has a significant impact on polymer interactions and drives the self-organization of inorganic-organic structures.     

标准化使我国酚醛胺(PAA)环氧树脂固化剂又上新台阶

介绍了酚醛胺(PAA)环氧树脂固化剂行业标准(行标)制定的背景与任务来源、工作过程、依据与技术内容的确定等,阐述了本行标及其标准化工作的重要性,提出了行标存在的不足和需要完善之处,表明了该行标推动我国酚醛胺环氧树脂固化剂行业又上新台阶。     

Fatigue Crack Growth in Epoxy/Aluminum and Epoxy/Steel Joints

The fatigue crack growth rate within epoxy/aluminum and epoxy/steel joints was evaluated as a function of a) type of surface pretreatment, b) water soak, c) fatigue cycle rate (Hz), d) adhesive thickness and e) type of epoxy adhesive.

For both adherends, aluminum and steel, a significant improvement in the fatigue behavior was obtained by use of a mercaptoester coupling agent. After an 8-day, 57°C water soak, the metal surfaces which were pretreated with coupling agent (CA) or by phosphoric acid anodization (PAA) still resulted in cohesive failure, while the controls had higher crack growth rate and showed greater scatter. The room-temperature cure matrix with CA-treated aluminum showed a less dramatic improvement, probably because of a known difference in the application procedure. For the steel joints and room-temperature adhesive the improvement in the fatigue behavior of CA-treated samples was maintained after the 8-day hot water soak. No significant change was found in the fatigue crack growth rate over a frequency range of 1 to 5 Hz, but a significant change was found as a function of the bondline thickness. The room temperature curing adhesive evaluated herein exhibited a much lower fatigue resistance than a heat-cured commercial structural adhesive FM-73.     

Enhanced oxygen‐barrier and water‐resistance properties of poly(vinyl alcohol) blended with poly(acrylic acid) for packaging applications

To enhance the oxygen‐barrier and water‐resistance properties of poly(vinyl alcohol) (PVA) and expand its food packaging applicability, five crosslinked poly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) blend films were prepared via esterification reactions between hydroxyl groups in PVA and carboxylic acid groups in PAA. The physical characteristics of the blends, including the thermal, barrier, mechanical and optical properties, were investigated as a function of PAA ratio. With increasing PAA content, the crosslinking density was significantly increased, resulting in changes in the chemical structure, morphology and crystallinity of the films. The oxygen transmission rate of pure PVA decreased from 5.91 to 1.59 cc m^?1 day^?1 with increasing PAA ratio. The water resistance, too, increased remarkably. All the blend films showed good optical transparency. The physical properties of the blend films were strongly correlated with the chemical structure and morphology changes, which varied with the PAA content. © 2016 Society of Chemical Industry     

分布式MEMS移相器桥高度与相移量的机电集成模型及应用

移相器是控制相控阵天线空间波束捷变的方向盘,其性能的优良决定着相控阵天线性能的高低。微机电系统(MEMS)移相器优势明显,但由于相控阵天线工作环境复杂,环境载荷会导致MEMS移相器结构变形,进而直接降低整个相控阵天线的性能。为此,该文研究MEMS移相器关键结构参数和电性能之间的耦合关系,将复杂环境要素对物理结构的影响传递到结构参数和电参数上,推导出分布式MEMS移相器的机电集成模型,并利用集成模型对变形MEMS移相器进行电性能快速评估和结构公差计算。仿真结果说明了集成模型的有效性和工程应用价值。     

Fundamentals, processes and applications of high-permittivity polymer-matrix composites

There is an increasing need for high-permittivity (high-k) materials due to rapid development of electrical/electronic industry. It is well-known that single composition materials cannot meet the high-k need. The combination of dissimilar materials is expected to be an effective way to fabricate composites with high-k, especial for high-k polymer-matrix composites (PMC). This review paper focuses on the important role and challenges of high-k PMC in new technologies. The use of different materials in the PMC creates interfaces which have a crucial effect on final dielectric properties. Therefore it is necessary to understand dielectric properties and processing need before the high-k PMC can be made and applied commercially. Theoretical models for increasing dielectric permittivity are summarized and are used to explain the behavior of dielectric properties. The effects of fillers, fabrication processes and the nature of the interfaces between fillers and polymers are discussed. Potential applications of high-k PMC are also discussed.     

Telechelic polymers by living and controlled/living polymerization methods

Telechelic polymers, defined as macromolecules that contain two reactive end groups, are used as cross-linkers, chain extenders, and important building blocks for various macromolecular structures, including block and graft copolymers, star, hyperbranched or dendritic polymers. This review article describes the general techniques for the preparation of telechelic polymers by living and controlled/living polymerization methods; namely atom transfer radical polymerization, nitroxide mediated radical polymerization, reversible addition-fragmentation chain transfer polymerization, iniferters, iodine transfer polymerization, cobalt mediated radical polymerization, organotellurium-, organostibine-, organobismuthine-mediated living radical polymerization, living anionic polymerization, living cationic polymerization, and ring opening metathesis polymerization. The efficient click reactions for the synthesis of telechelic polymers are also presented.     

适于毫米波应用的新型MEMS实时延时线(英文)

介绍了两种适于毫米波应用的RF MEMS实时延时线的设计。首先,在设计中采用了一种新颖的RF MEMS拓宽调节范围的变容器结构,得到了最大变容比为5.39的在片测试结果。其工艺设计基于表面微机械工艺,采用了由5个掩模版组成的工艺流程。然后,在RF MEMS变容器设计的基础上,完成了用于原理论证的Ka波段RF MEMS实时延时线的仿真设计、工艺流片和在片测试。Ka波段RF MEMS实时延时线的在片测试结果显示,在28GHz时处于下降状态的插入损耗为-2.36dB;两端口在28GHz时的回波损耗都小于-15dB,而在5～40GHz的整个测试频率范围内的回波损耗都小于-10dB。在Ka波段RF MEMS实时延时线设计基础上,60GHz RF MEMS实时延时线的仿真设计已经完成并准备投片。     

PAA类黏结剂在锂电池中电化学性能研究进展

黏结剂是维持极片完整性必不可少的部分,对电池比容量、循环稳定等性能的提高非常重要。聚丙烯酸(PAA)因含有较多极性官能团,可溶于水,而被用作锂电池正负极黏结剂。PAA黏附性好,但极性基团使得分子链间形成的氢键导致PAA链刚性较大,不利于维持充放电过程中极片的完整性,因此,控制PAA官能团数量、改变官能团种类及PAA分子链结构,对锂电池电性能的提高势在必行。本文综述了近几年锂电池用PAA黏结剂的研究进展,重点介绍了PAA黏结剂的结构特性、改性及应用方式及其对不同种锂电池首次库伦效率、循环稳定性和阻抗性能的影响,并对PAA黏结剂的未来改性研究热点做了展望,探索PAA引入不同结构的弹性或导电聚合物后,对于黏结剂本身性能的影响,改善界面性能,以适用于不同活性材料正负极,提高锂离子传输速率,更好地提高锂电池的使用性能。     

纳米LiCo_xMn_(2-x)O_4粉体的制备与电化学性能

采用溶胶一凝胶法并结合热处理工艺制备LiCoxMn2-xO4粉体,结合热处理工艺制备Li-LiCoxMn2-xO4粉体.利用热重一差热分析、X射线衍射、透射电镜、充放电测试等方法对前驱体的热分解行为、粉体的结构、形貌及电化学性质进行了表征,同时研究了钴掺杂量对其结构和电化学性能的影响.结果表明,直接以聚丙烯酸(PAA)为螯合剂合成了稳定的溶胶和凝胶,进一步获得了粒径分布均匀、无团聚的尖晶石LiCoxMn2-xO4纳米粉体.随着钴掺杂量的增加,晶格常数、晶粒尺寸逐渐减小,晶格畸变逐渐增大,但对尖晶石结构影响较小;LiCoxMn2-xO4粉体的放电比容量随着x值增大略有降低,但循环性能得到明显的改善.在电流密度0.1mA/cm2、截止电压3.5～4.3V时,粒径约80hm的LiCo0.1Mn1.9O4粉体首次放电比容量达135mAh/g,20次循环后的稳定放电比容量为118mAh/g,且每次容量衰减低于0.2%,具有较好的电化学性能.