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Synthesis of Yolk/Shell heterostructures MOF@MOF as biomimetic sensing platform for catechol detection
No full textMetal-organic frameworks (MOFs) have potential as heterogeneous biomimetic catalysts due to their high surface area, tunable porosity, and diversity of metals and functional groups. However, the activity and substrate specificity of pure monomeric MOFs still must be improved. Here, a size-selective MOF coating on the external surface of a biomimetic MOF is used to overcome these limitations of pure monomeric MOFs. The synthesis process of the biomimetic material involved first the coating of porous coordination network (PCN-222) cores with polyvinylpyrrolidone (PVP) as a structure-directing agent and then the modification of zeolitic imidazolate frameworks (ZIF-8). The yolk/shell PCN-222@ZIF-8-based sensor showed high selectivity for catechol but not for dopamine or L-DOPA. The PCN-222@ZIF-8 hybrid material-based sensor displayed 10 times more sensitivity than the PCN-222-based sensor, with low limit of detection (LOD) at 33 nmol L-1. Thus, ZIF-8 is a shell which allows the diffusion of specific substrate to the active sites of the PCN-222 and enriches the substrate. Furthermore, the PCN-222@ZIF-8 exhibits solvent adaptability, which overcomes the drawback of the natural HRP enzyme. This work opens a new avenue for construction of MOF@MOF biomimetic sensors and other applications
Temperature-induced wear transition in ceramic-metal composites
No full textWear degradation is a key parameter to evaluate the performance of ceramic-metal composites applied in manufacturing and mining industries. We selected a typical composite (high Mn steel + 50 wt.% TiC) as the model system and studied its wear behavior. The integrity and damage of TiC ceramic particles were analyzed under different temperatures and atmospheres. A critical temperature of similar to 125 degrees C at which transitions of wear mechanism occurred was observed for the first time. Below this temperature, hardness dominated the wear behavior as the presence of oxygen induced surface decarburization of ceramic particles with an increased wear rate. The thermodynamics of oxygen-assisted decarburization were investigated using the CALPHAD (CALculation of PHAse Diagram) approach, and the resultant hardness reduction of TiC particles was clarified using density functional theory (DFT) calculations. At temperatures above 125 degrees C, toughness became the governing factor as the ceramic-metal deformation incompatibility induced fracture of ceramic particles. The formation of nano-crystalline oxide tribolayers improved the fracture toughness of ceramic particles and restrained the wear loss, which was elucidated using DFT calculations. Thus, the current work has delineated the competitive micro-mechanisms consisting of surface decarburization and toughening of ceramic particles, which could be used to interpret the wear behavior of ceramic-metal composites. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved
Polyethylene Terephthalate-Based Materials for Lithium-Ion Battery Separator Applications: A Review Based on Knowledge Domain Analysis
No full textAs the key material of lithium battery, separator plays an important role in isolating electrons, preventing direct contact between anode and cathode, and allowing free passage of lithium ions in the electrolyte. Polyethylene terephthalate (PET) has excellent mechanical, thermodynamic, and electrical insulation properties. This review aims to identify the research progress and development trends of PET-based material for separator application. We retrieved published papers (2004-2019) from the Scientific Citation Index Expanded (SCIE) database of the WoS with a topic search related to PET-based material for separator application. The research progress and development trends were analyzed based on the CiteSpace software of text mining and visualization
Mechatronics design and testing of a cable-driven upper limb rehabilitation exoskeleton with variable stiffness
No full textIn this paper, we present a cable-driven exoskeleton with variable stiffness for upper limb rehabilitation. Adjustable stiffness of the cable-driven exoskeleton is achieved by attaching a novel variable stiffness module (VSM) to each driving cable. The module is able to vary stiffness in a large range through changing cable tension. In this paper, a stiffness model is developed for a cable-driven exoskeleton to reveal the stiffness performance of the exoskeleton with the influence of VSMs. Based on the stiffness model, a controller with stiffness-oriented strategy is proposed to vary the stiffness of the exoskeleton. Experiments on a prototype of a cable-driven exoskeleton are conducted to validate the controller
Construction of shape-memory carbon foam composites for adjustable EMI shielding under self-fixable mechanical deformation
No full textThe design and fabrication of novel electromagnetic interference (EMI) shielding materials with the capability of realizing convenient performance regulation under self-fixable mechanical deformation is becoming an urgent challenge due to the increasingly complex application conditions. To alleviate this problem, the composite construction that consisted of compressible carbon foam (CF) and shape-memory polymer coating was proposed, and the demo samples were fabricated by coating trans-1,4-polyisoprene (TPI)-MXene layer onto compressible wood-derived CF with multilayer microstructure. The resultant composites (thickness: similar to 2-10 mm, density: similar to 150 mg/cm(3)) with enhanced shielding effectiveness (SE) of similar to 25.3-44.7 dB could not only adjust their SE value by changing their compressive strains, but also possess excellent thermally/electrically stimulated shape memory behaviors that can be easily deformed and recovered as being heated and fix a temporary shape at low temperature, thereby realizing convenient SE regulation under self-fixable mechanical deformation. Moreover, based on different initial SE performance and compression conditions, the EMI SE of the composites can also be tuned within effective SE range of 20 dB, or switched between > 20 and < 20 dB, exhibiting smart function-tunable or function-switchable feature, which provides a promising platform for developing novel EMI shields for smart electromagnetic response applications
Fabrication of Core-Shell Chopped C-f-Phenolic Resin Composite Powder for Laser Additive Manufacturing of C-f/SiC Composites
No full textLaser additive manufacturing is a promising technique for the preparation of complex-shaped SiC composites. High-quality powders are critical for high-precision laser printing. In this work, core-shell C-f @phenolic resin (PR) composites for selective laser sintering of carbon fiber reinforced silicon carbide (C-f/SiC) composites were fabricated by surface modification using 3-aminopropyltriethoxy silane coupling agent (KH550) in combination with planetary ball milling. PR coated uniformly on the fiber surface to form a core-shell structure. The effects of PR on the morphology, elemental composition, interfacial interactions, and laser absorption of the core-shell composite powder were investigated in detail. Results indicated that the composite powder exhibited good laser absorption within the infrared band
Multicolor Fluorescent Polymeric Actuator with Self-Sustained Oscillation Behavior
No full textSoft fluorescent polymeric films are receiving increasing attention in the fields of sensing, display, information encryption, and so on. However, a few attempts are conducted to heterogeneously integrate fluorescent polymeric films with other soft polymeric materials into topology-optimized architectures (e.g., bilayer and pattern), which may lead to as-yet-unimagined performance. Herein, the synthesis of novel multicolor fluorescent polymeric films is presented via dynamic lanthanide coordination, followed by the fabrication of bilayer actuators with unique self-sustained oscillation behavior. The polymeric films are prepared from polydimethylsiloxane (PDMS) oligomer containing 2,6-pyridinediimine ligands that can chelate with Eu3+/Tb3+ ions to trigger vivid red/bluish green fluorescence via antenna effect. After being further interfacially engineered with pan paper, fluorescent bilayer actuators are prepared, which display reversible 2D/3D shape deformation in response to environmental temperature changes owing to the mismatch between thermal expansion abilities of two layers. Interestingly, when placing the bilayer actuator with one end fixed near a constant heat source, quite unique self-sustained oscillation behavior is observed, which encourages to explore their potential applications as dynamic alarming devices. The present study broadens the list of fluorescent polymeric films and suggests the huge potential of multimaterial integration to develop powerful functional materials with versatile uses
First-principles studies on behaviors of He impurities in d-MAX phase Zr3Al3C5
No full textUnderstanding helium (He) incorporation into materials is essential to estimate the material performance in a nuclear environment for the fabrication of nuclear devices. The effect of helium irradiation on Zr3Al3C5 was studied by using the first-principles method. It is found that the He interstitial atoms tend to situate in the Al-C layers in Zr3Al3C5. The calculation of defect formation energy shows that the defects at the Zr sites are the most difficult to form, while vacancies at the Al and C sites are more ready to form in Zr3Al3C5. The numbers of He atoms that can be trapped by an Al(2) and a C(3) vacancy are seven and three, respectively, which show that Al vacancies have a stronger ability to trap He atom than C vacancies. The migration of He in Zr3Al3C5 is also investigated. The results indicate that He impurity atoms migrate more easily along the c-axis than in the a-b basal plane in the Al-C layer. The diffusion barrier of He atom from the Al-C into the Zr-C layer is determined to be 3.13 eV. The results imply that the Al-C layers tend to be disordered while the Zr-C layers exhibit good tolerance of damage under He irradiation. Additionally, we also studied the stress-strain relationships of Zr3Al3C5 under tensile and shear loading, with the ideal tensile strength and shear strength of Zr3Al3C5 predicted. (C) 2020 Published by Elsevier B.V
Beyond Superwetting Surfaces: Dual-Scale Hyperporous Membrane with Rational Wettability for Nonfouling Emulsion Separation via Coalescence Demulsification
No full textMembrane fouling is the obstacle that limits the practical application of membranes in efficient oil/water separation. The main reason for membrane fouling is the deposition of the dispersed phase (e.g., oil) on the membrane surface based on the sieving effect. The key challenge for solving the fouling problem is to achieve fouling removal via rationally considering hydrodynamics and interfacial science. Herein, a poly(vinylidene fluoride) membrane with a dual-scale hyperporous structure and rational wettability is designed to achieve a continuous nonfouling separation for oil/water emulsions via membrane demulsification. The membrane is fabricated via dual-phase separation (vapor and nonsolvent) and modified by in situ polymerization of poly(hydroxyethyl methylacrylate) (contact angle 59 +/- 1 degrees). The membrane shows stable permeability (1078 +/- 50 Lm(-2)h(-1)bar(-1)) and high separation efficiency (>99.0%) in 2 h of continuous cross-flow without physicochemical washing compared to superwetting membranes. The permeation is composed of two distinct immiscible liquid phases via coalescence demulsification. The surface shearing and pore throat collision coalescence demulsification mechanism is proposed, and rational interface wettability facilitates the foulant/membrane interaction for nonfouling separation. Beyond superwetting surfaces, a new strategy for achieving nonfouling emulsion separation by designing membranes with a dual-scale hyperporous structure and rational wettability is provided
Comprehensive review on plant fiber-reinforced polymeric biocomposites
No full textThe expansion of environment-friendly materials based on natural sources increases dramatically in terms of biodegradable, recyclable, and environmental disputes throughout the world. Plant-based natural fiber, a high potential field of the reinforced polymer composite material, is considered as lightweight and economical products as they possess lower density, significant material characteristics, and extraordinary molding flexibility. The usage of plant fibers on the core structure of composite materials have drawn significant interest by the manufacturers to meet the increasing demand of the consumers for sustainable features with enhanced mechanical performances and functionalities. The plant fiber-based composites have widespread usage in construction, automotive, packaging, sports, biomedical, and defense sectors for their superior characteristics. Therefore, this critical review would demonstrate an overview regarding the background of natural fiber composites, factors influencing the composite properties, chemical interaction between the fiber and matrices, future potentiality, and marketing perspectives for triggering new research works in the field of biocomposite materials