Emanation thermal analysis study of a sol-gel precursor for silica-titania waveguides

Emanation Thermal Analysis (ETA) was demonstrated as a tool for the characterization of microstructure changes of a sol-gel precursor for silica-titania layers deposited on the glass plate to be used as planar waveguides. Temperature ranges of 280-330 and 380-500°C, respectively, in which the densification of the layers took place, were determined by ETA under in situ conditions of the sample heating. Results of thermogravimetry were compared with the ETA data. This revised version was published online in August 2006 with corrections to the Cover Date.     

横观各向同性层状场地对环形简谐荷载的位移响应

本文采用横观各同性层状粘弹性模型拟半空间上之的层状场地,用阻尼器取代其下部的半空间以吸收振动能量。     

反式钙钛矿电池超薄空穴传输层研究进展

空穴传输层(HTLs)厚度对反式钙钛矿太阳能电池(PSCs)性能具有重大影响,因其显著影响太阳光透过和HTLs的空穴传输性能。几个纳米至十几个纳米厚度的超薄HTLs在减少伴生吸收、电荷传输损失和材料消耗等方面具有明显优势。目前,有许多成熟的制备超薄无机HTLs的方法,并在反式和叠层PSCs中得到广泛研究与应用。最近,一些关于有机超薄HTLs的新型制备方法也展现出良好的性能并逐渐引起相关领域研究者关注。在此,本文主要总结反式PSCs中超薄HTLs的研究进展与应用,关注其未来发展的挑战和方向,为该领域进一步的研究提供参考。     

Consistency of surface mechanical properties of spread protein layers at the liquid–air interface at different spreading conditions

Π/A isotherms of spread β-lactoglobulin and β-casein at the air–water interface are measured under different spreading conditions. While the isotherms do not show drastic effects of the spreading concentration and the compression rate the interfacial shear rheological behaviour is significantly influenced. In particular, the shear viscosity of β-lactoglobulin layers depend directly on the spreading concentration. Significant viscosity increase is obtained at larger surface pressures when the spreading concentration is increased. In contrast the shear rheology of the spread β-casein layers can be normalised by plotting the viscosities as a function of the surface pressure Π. The different behaviour is discussed in terms of denaturation of the β-lactoglobulin during the monolayer formation process by adsorption from the spread thin protein solution layer.     

Influence of operational parameters on retention of ultra-high molecular weight polystyrenes in thermal field-flow fractionation

Summary The influence of various parameters (concentration of the injected polymer solution, flow rate, temperature gradient, relaxation conditions) on the retention and shape of the fractogram of ultra-high molecular weight polystyrenes in thermal field-flow fractionation was investigated. Under the operating conditions adopted, reproducible oscillations in the peak shape are observed for molecular weights larger than a few millions, especially at relatively high polymer concentration. They are attributed to some hydrodynamic instabilities. The retention of ultra-high molecular weight polystyrenes at high flow rate is strongly dependent on the initial relaxation period. All of the investigated operational variables have a complex effect on the resulting shape of the fractogram. Consequently, the confirmation of the shear-induced focusing of macromolecules across the channel thickness requires further study. Experiments on reinjection of fractions collected after an initial high speed pass through the separation system leads to the conclusion that shear degradation of the ultra-high molecular weight polymers did not occur under the investigated experimental conditions even at the highest flow rates.     

Nanoscale imaging of oxidized copper foil covered with chemical vapor deposition-grown graphene layers

Characterization of the geometrical and structural characteristics of oxidized Cu area in high resolution is crucial for tracking the change in morphology, exploring interactions between graphene layers and Cu substrates and revealing the mechanism for the orientation-dependent oxidation of Cu. Here, we reported experimental results on nanoscale imaging of natural oxidation of the polycrystalline Cu substrate coated by partial-coverage chemical vapor deposition (CVD)-grown graphene stored in dryer under ambient conditions for up to 10 months. Scanning electron microscope (SEM), together with atomic force microscope (AFM), Raman, and X-ray photoelectron spectroscopy (XPS), was used for systematically studying the morphological and compositional changes at nanoscale during oxidation. The appearance of oxidized Cu substrates could be unambiguously distinguished from the unoxidized regions based on their distinctly different morphologies in SEM images, and the underlying mechanism was discussed in detail. By analyzing a millimeter-seized polycrystalline Cu substrate, we found that the oxidation of polycrystalline Cu substrate depends sensitively on both orientation of graphene layers and Cu substrates. Furthermore, the time-dependent oxidation evolution of Cu substrate was also established, and the oxidation rate was readily determined. The findings reported here will have important implications for developing protection coatings for Cu.     

Shear banding in semidilute entangled polymer solutions

Shear banding in semidilute polymer solutions and other soft materials is one of the most intensely debated topics in current rheology. By means of rheo-optical experiments, physical modeling, and numerical simulations, researchers have started to develop a more thorough understanding of this flow instability within the past few years. Nevertheless, much effort is still required to identify the exact microscopic mechanisms leading to shear band formation and to clarify whether the phenomenon is universal for polymers. For this purpose, basic rheological characteristics, such as the appearance of a stress overshoot during start-up of a simple shear flow, have to be revisited and better related to the dynamics of the polymeric network.     

剪切对玻璃珠填充聚丙烯结晶行为的影响

应用Linkam CSS450剪切仪、广角X射线衍射仪(WAXD)和小角X射线散射仪(SAXS)等研究了剪切对玻璃珠填充聚丙烯结晶行为的影响, 结果表明, 与纯聚丙烯相比, 填加玻璃珠的聚丙烯体系中, 玻璃珠起到成核剂的作用, 不利于β晶的生成. 玻璃珠直径较小(4 μm)时, 剪切对聚丙烯β晶的生成影响较小; 当玻璃珠直径增加到35 μm时, 剪切速率为20 s-1左右最有利于β晶生成; 剪切速率和玻璃珠直径的增加, 有利于聚丙烯片晶的取向, 而且玻璃珠含量越高, 片晶的取向程度越大.     

Non-linear Viscoelastic Rheological Properties of PCC/PEG Suspensions

The shear thinning and shear thickening rheological properties of PCC/PEG suspension were investigated with the increase of oscillatory amplitude stress at different constant frequencies. The results show that the complex viscosity was initially independent of stress amplitude and obvious shear thinning occurred, then dramatic shear thickening took place after reaching the minimum viscosity. Typically, in a constant frequency of 5 rad/s, the elastic modulus, viscous modulus, and tanδ （δ is the out-of-phase angle） vs. the stress amplitude was investigated. It is found that the elastic modulus initially appeared to be independent of stress amplitude and then exhibited a rapid decrease, but the viscous modulus was independent of amplitude stress at lower amplitude stress. After reaching the minimum value the viscous modulus showed a rapid increase. On the other hand, tanδ increased from 0.6 to 92, which indicates that the transition from elastic to viscous had taken place and tanδ showed a steep increase when shear thickening occurred. Lissajous plots are shown for the dissipated energy vs. different maximum stress amplitude in the shear thinning and shear thickening regions. The relationship of dissipated energy vs. maximum stress amplitude was determined, which follows a power law. In the shear thinning region the exponent was 1.91, but it steeply increases to 3.97 in the shear thickening region.