The Mechanical Deformation Process of Electrospun Polymer Nanocomposite Fibers

Summary: The mechanical deformation processes of poly(methyl methacrylate)/ montmorillonite nanocomposites and their electrospun fibers were investigated by in situ tensile tests under a transmission electron microscope depending on their morphology. While the polymer nanocomposites deformed in a brittle manner, i.e., crazing, the electrospun polymer nanocomposite fibers deformed through a shear flow process leading to “nanonecking” due to the strong overlap of stress fields caused by nanopores within the fiber under a uniaxial tensile load. This unique change in deformation behavior provides the possibility that the intrinsic brittle material could be manipulated to be ductile without sacrificing its other attractive properties through a well‐controlled electrospinning process.

TEM micrograph of a low temperature fractured fiber showing the nanoporous surface structure.     

低介电常数介质薄膜的研究进展

用低介电常数介质薄膜作金属线间和层间介质可以降低超大规模集成电路(ULSI) 的互连延迟、串扰和能耗。从介质极化的原理出发,揭示了开发低介电常数介质薄膜的可能途径;综述了低介电常数介质薄膜的制备方法、结构与性能表征、工艺兼容性等领域的最新进展。     

氧化石墨烯量子点修饰氧掺杂多孔g-C3N4在光催化降解和抗菌中的应用（英文）

偶氮类合成色素具有遗传毒性、致癌性和致泻性,而食源性致病菌易引发细菌性感染和食物中毒事件,食品加工过程中产生的色素废水和致病菌废水若未经妥善处理就排入水体,会对水体及环境造成污染,废水中的偶氮类色素和致病菌还会通过食物链对人体健康产生威胁.因此,寻求更为高效、绿色、安全的处理技术和净化材料有效去除食品废水中高污染性和毒害性的偶氮类色素和致病菌显得尤为迫切.g-C3N4是一种具有可见光响应的有机半导体光催化材料,广泛应用于降解污染物、杀灭致病菌、催化有机反应等领域.然而,g-C3N4本身存在着比表面积小、光吸收性能差、光氧化能力低以及光生载流子迁移效率低等缺点,限制了其光催化性能.针对上述问题,我们对g-C3N4的空间和电子结构进行了设计,将形貌调控、元素掺杂和助催化剂修饰三种改性方法相结合,以获得兼具大比表面积、优异光吸收性能、强氧化能力以及快速光生载流子迁移能力的高活性g-C3N4基光催化体系.本文通过水热法制备了氧掺杂多孔氮化碳(PCNO),通过酸剥离法制备了氧化石墨烯量子点(ox-GQDs),最后通过自组装法将助催化剂ox-GQDs修饰到PCNO上,制备了ox-GQDs/PCNO复合光催化剂.零维的ox-GQDs可以通过氢键、π-π作用和化学键作用,与二维的PCNO实现紧密接触,均匀地分散在PCNO的表面和内部孔道上.由于ox-GQDs独特的上转换特性、电子捕获能力和过氧化物酶活性,ox-GQDs/PCNO复合光催化剂具有比PCNO更佳的光吸收性能、更高的电荷转移效率以及更强的光氧化能力.因此,ox-GQDs/PCNO复合材料在降解偶氮类色素和杀灭致病菌方面均表现出更为优异的可见光催化性能,活性最佳的复合材料ox-GQDs-0.2%/PCNO降解偶氮类色素苋菜红的速率常数约是PCNO的3.1倍,并且该材料能在可见光照射4 h内杀灭99.6%的大肠杆菌,远超过PCNO 31.9%的抗菌活性.另外,光生空穴、超氧自由基和羟基自由基被证实是ox-GQDs/PCNO体系在光催化反应中产生的活性物种,可以彻底矿化偶氮类色素并有效杀灭致病菌.本研究可以拓展g-C3N4基光催化剂在环境净化领域的应用前景,并为阐明ox-GQDs在复合光催化体系中的作用提供新的见解.     

Mechanical properties of bulk single crystalline nanoporous gold investigated by millimetre-scale tension and compression testing

In this work, the mechanical behaviour of millimetre-scale, bulk single crystalline, nanoporous gold at room temperature is reported for the first time. Tension and compression tests were performed with a custom-designed test system that accommodates small-scale samples. The absence of grain boundaries in the specimens allowed measurement of the inherent strength of millimetre-scale nanoporous gold in tension. The elastic modulus and strength values in tension and compression were found to be significantly lower than values measured with nanoindentation-based techniques and previously reported in the literature, but close to those reported for millimetre-scale polycrystalline samples tested using traditional compression techniques. Fracture toughness was found to be very low, in agreement with the macroscopic brittleness of nanoporous gold, but this is due to the localization of deformation to a narrow zone of ligaments, which individually exhibit significant plasticity and necking.     

The mechanical response of core-shell structures for nanoporous metallic materials

Nanoporous gold (NP-Au) exhibits microscale plasticity, but macroscopically fails in a relatively brittle manner. This current study suggests that a core-shell structure can increase both ductility and strength of NP-Au. A core Au foam structure was created using conventional dealloying methods with average ligament size of 60?nm. Nickel was then electroplated on to the NP-Au with layer thicknesses ranging from 2.5?nm to 25?nm. Nanoindentation demonstrated a significant increase in the hardness of the coated Np-Au, to about five times of that of the pure Np-Au, and a decrease in creep by increasing the thickness of the coated Ni layer. Molecular dynamics simulations of Au–Ni ligaments show the same trend of strengthening behavior with increasing Ni thickness suggesting that the strengthening mechanisms of the Np-Au are comparable to those for fcc nano ligaments. The simulations demonstrate two different strengthening mechanisms with the increased activity of the twins in plated Au–Ni ligaments, which leads to more ductile behavior, as opposing to the monolithic Au ligaments where nucleation of dislocations govern the plasticity during loading.     

Auto‐barrier‐thinning effect under rapid anodization of nanoporous alumina membrane

We have developed a rapid non‐steady anodization technique that leads to an in‐situ auto‐thinning of the barrier layer due to a space charge limited condition that modifies the local fields at the interfaces of the Al‐Al₂O₃‐electrolyte ternary system. Unlike steady‐state growth, in this non‐steady case an unequal movement of the boundaries of barrier takes place which etches the electrolyte‐oxide interface more than the oxide grows at the oxide‐metal interface, leading to a thinner barrier layer and favouring its complete removal via wet‐etching process. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrochemical synthesis of silver nanoparticles-coated gold nanoporous film electrode and its application to amperometric detection for trace Cr(VI)

A simple and rapid approach for the electrochemical synthesis of Ag nanoparticles-coated gold nanoporous film (AgGNF) on a gold substrate was reported. The solid gold electrode (SGE) was directly anodized under a high potential of 5 V, and then reduced to obtain gold nanoporous film (AuNF) by freshly prepared ascorbic acid. The Ag nanoparticles (AgNPs) were grown on the AuNF electrode by potential-step electrodeposition. The resulting AgGNF composites electrodes were characterized by scanning electron micro...