Key Engineering Materials Vol. 894

Abstract: In the past years, azobenzene, as a common photoreactive group, has been widely used in intelligent photocontrolled supramolecular gels. In the field of biomedicine, a few supramolecular hydrogels based on azobenzene are regarded as carriers with low damage and high control in vivo due to their advantages in light response. In the environmental field, some hydrogels can also adsorb pollutants under the control of light through the interaction between host and guest. At the same time, supramolecular hydrogels based on azobenzene with multiple stimulus responses have been studied. It is difficult for most supramolecular organogels to have multiple stimulus responses simultaneously and the preparation conditions are also more complex. In this paper, I have summarized the latest research results of supramolecular hydrogels and organogels based on azobenzene in recent years so that researchers can have a deeper understanding of the preparation methods, properties and application of the supramolecular gels containing azobenzene.

Abstract: Terahertz technology can be used in sensing and communication applications. We designed a polarization-sensitive photodetector specially for Terahertz frequency based on cross-shaped graphene sheet. The shaped graphene excites localized surface plasmon which can enhance the absorption of incident light. From the Finite Difference Time Domain Solutions (FDTD), we figured out that transmission of incident light relates to the size of photodetector, polarization angle and physical properties of graphene such as chemical potential and layers. The transmission can be tuned as low as 8.3 ×10^-5 when we set the size at 14×6µm and 14×5µm for two different graphene pieces and polarization angle as 0°, at room temperature. This device we designed can absorb Terahertz at a wavelength around 126 µm, which can be used in THz application applied in future high-tech communication or safety inspection.

Abstract: Covalent organic frameworks (COFs) are a new category of materials and developing fast in recent years. COFs present low density, controllable porosity, and high surface area. Based on these merits, COFs have great potential in various applications, such as gas separation and storage, energy storage, catalysis, and many others. In this review, we summarize the synthesis of COFs from the aspects of design principles and synthetic reactions. In particular, we categorize the synthetic reactions of also COFs into six categories and introduce the advantages of each type of reaction. Moreover, we utilize several examples to illustrate how to construct COFs by these synthetic methods. In the end, a future perspective on the development of new synthetic methods for COFs is briefly mentioned.

Abstract: Piezo-chromic oxides are able to mark pressure or strain by a drastic color change. In this paper, CoMoO4 molybdate compound and related thermoset composites were prepared in lab. The distribution of CoMoO4 oxide in the thermoset matrix was first investigated via SEM. Moreover, the effects on the thermal and mechanical properties with the addition of CoMoO4 oxide were further analyzed. The piezo-chromic characteristic for CoMoO4 incorporated thermoset composites were verified with compression test. The color change can be clear visualized at a strain level close to the yield point of the composite blends. This study has the potential to open new directions to piezo-chromic polymeric materials as early damage detector.

Abstract: Four different plastic deformation modes of pure molybdenum in powder metallurgy were studied, including single tensile, single torsion, tensile-torsion and compressive-torsion. Then the influence of these four plastic deformation modes on the micro-mechanical properties of pure molybdenum in powder metallurgy was studied by the micro-indentation method. The results show that the accumulated strain before deformation instability or fracture of the studied material caused by different plastic deformation modes is different, while showing a regular variation. And the mean indentation hardness along the radial direction of the sample also change regularly, which results in different strengthening effects on the molybdenum material itself. The damage inside the deformed material will cause the apparent modulus of elasticity measured by micro-indentation to decrease significantly.

Abstract: DME has been received the attention as a renewable energy due to its thermal efficiencies equivalent to diesel fuel, lower NO_x emission, near-zero smoke and non-toxic. DME can be obtained by methanol dehydration over solid acid catalysts or directly from syngas over bifunctional catalysts. The catalytic dehydration of methanol to DME has been widely studied in the literature over pure or modified γ -aluminas (γ-Al₂O₃) and zeolites. Mesoporous silica has obtained much consideration due to its well-defined structural order, high surface area, and tunable pore diameter. In this work, sulfonic acid and aluminium modified mesoporous silica were synthesized and tested as catalysts for production of dimethyl ether from methanol. The modified silicas were studied utilizing XRD, N₂ physisorption, pyridine adsorption, and scanning electronic microscopy. The effects of reaction temperature and water deactivation on the methanol selectivity and conversion to dimethyl ether were investigated. Sulfonic acid modified mesoporous silica showed higher selectivity and stability of DME than that of aluminosilicate. The grafting of mesoporous silica with sulfonic groups displayed much more enhanced hydrothermal stability than Al-MCM-41 and γ-Al₂O₃.

Abstract: Electroplating on polymer substrates, which provides polymers with enhanced mechanical properties, extended component lifetimes, and offers a decorative appearance, is environmentally unsustainable. Laser machining, a green process developed at Cirrus Materials Science Ltd, generates an array of pores on various polymer surfaces, which replaces the chemical etch process, and provides strong adhesion for metal coatings to polymer substrates. Laser machining is also applicable to a wide range of engineered or industrial polymer substrates and is adaptable to complex shapes and 3D printed parts. This paper discussed the process of laser machining of polymer substrates including the properties of metal layers on such machined surfaces; and demonstrated laser machining as a promising substitute for conventional chemical etching to prepare various engineering polymer substrates for adhesive coatings.

Abstract: Due to the development of various mobile electronic devices, such as electric vehicles, rechargeable ion batteries are becoming more and more important. However, the current commercial lithium-ion batteries have obvious defects, including poor safety from Li dendrite and flammable electrolyte, quick capacity loss and low charging and discharging rate. It is very important to find a better two-dimensional material as the anode of the battery to recover the disadvantages. In this paper, first principles calculations are used to explore the performances of VS₂ bilayer and VS₂ / graphene heterostructure as the anodes of Li ion batteries. Based on the calculation of the valences, binding energy, intercalation voltage, charge transfer and diffusion barrier of Li, it is found that the latter can be used as a better anode material from the perspective of insertion voltage and binding energy. At the same time, the former one is better in terms of diffusion barrier. Our study provides a comprehensive understanding on VS₂ based 2D anodes.

Abstract: This work is devoted to the formulation and search of an analytical solution for the problem of the interaction of a rigid cylindrical body and a pipe with an inner coating in the case when the cylinder is placed inside such a pipe. It is assumed that the pipe coating can have a strong nonuniformity, and its thickness depends on the longitudinal coordinate. A special approach used in this work allows obtaining analytical solutions in which functions related to the properties and profile of the coating are separated by separate terms and factors. This allows us to provide efficient calculations even in cases where coating characteristics are described by complex functions. Other known methods lead to significant calculation errors.