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Today: 11 April 2021, Sunday.

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#1

 

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Description Hydrogels are flexible materials that have high potential for use in various applications due to their unique properties. However, their applications are greatly restricted by the low mechanical performance caused by high water content and inhomogeneous networks. This paper reports a universal strategy for easily preparing hydrogels that are tough and stretchable without any special structures or complicated processes. Our strategy involves tuning the polymerization conditions to form networks with many polymer chain entanglements to achieve energy dissipation. Tough and stretchable hydrogels can be prepared by free radical polymerization with a high monomer concentration and low cross-linker content to optimize the balance between physical and chemical cross-links by entanglements and covalent bonds, respectively. The strategy of using polymer chain entanglements for energy dissipation allows us to overcome the limitation of low mechanical performance, which leads to the wide practical use of hydrogels. A universal method for easily preparing tough and stretchable materials for biomedical applications has been developed by scientists in Japan. Hydrogels are highly absorbent networks of polymers. With a water content of up to 90%, they have a soft, spongy and flexible texture and can potentially be used as artificially engineered tissue and in wound healing. However, hydrogels with a high water content or an irregular network can be mechanically weak and brittle. Takashi Miyata and colleagues from Kansai University in Osaka discovered polymerization conditions to form networks of heavily entangled polymer chains in general polymerzations. Their approach optimized the balance between physical and chemical chain links, which improved the hydrogel’s mechanical performance. This improvement means that hydrogels could be used in an even wider variety of applications. This paper reports a universal strategy for easily preparing hydrogels that are tough and stretchable without any special structures or complicated processes. Tough and stretchable hydrogels are prepared by tuning the polymerization conditions to form networks with many polymer chain entanglements to achieve energy dissipation. The strategy allows us to overcome the limitation of low mechanical performance, which leads to the wide practical use of hydrogels.

#Materials
Field # Materials
Updated 09 April 2021

#2

 

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Description The discovery and control of new phases of matter is a central endeavour in materials research. The emergence of atomically thin 2D materials, such as transition-metal dichalcogenides and monochalcogenides, has allowed the study of diffusive, displacive and quantum phase transitions in 2D. In this Review, we discuss the thermodynamic and kinetic features of 2D phase transitions arising from dimensionality confinement, elasticity, electrostatics, defects and chemistry unique to 2D materials. We highlight polymorphic, ferroic and high-temperature diffusive phase changes, and examine the technological potential of controlled 2D phase transitions. Finally, we give an outlook to future opportunities in the study and applications of 2D phase transitions, and identify key challenges that remain to be addressed. Phase transformations in 2D materials have distinct kinetic and thermodynamic features, resulting from their reduced dimensionality and unique interactions. This Review discusses the properties of phase transitions and defects in 2D materials, and examines technological applications and challenges in the study of 2D phase transitions.

#Materials
Field # Materials
Updated 09 April 2021

#3

 

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Description 3D printing using conventional stereolithography is challenging because the polymerized layers adhere to the solid constraining interface. The mechanical separation forces lead to poor process reliability and limit the geometrical design space of the printed parts. Here, these challenges are overcome by utilizing a static inert immiscible liquid below the resin as the constraining interface. We elucidate the mechanisms that enable the static liquid to mitigate stiction in both discrete layer-by-layer and continuous layerless growth modes. The inert liquid functions as a dewetting interface during the discrete growth and as a carrier of oxygen to inhibit polymerization during the continuous growth. This method enables a wide range of process conditions, such as exposure and resin properties, which facilitates micrometer scale resolutions and dimensional accuracies above 95%. We demonstrate multi-scale microstructures with feature sizes ranging from 16 μm to thousands of micrometers and functional devices with aspect ratios greater than 50:1 without using sacrificial supports. This process can enable additive 3D microfabrication of functional devices for a variety of applications. Stiction between polymerized layers and the constraining solid interface during stereolithography limits resolution. Here, a static inert liquid is used as a constraining interface to mitigate stiction, enabling high resolution parts to be fabricated with feature sizes spanning tens to thousands of microns.

#Materials
Field # Materials
Updated 09 April 2021

#4

 

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Description This study describes the development of a fog collector material for fog harvesting. Polypropylene (PP) doped with fumed silica (0–2%) was punctured at equal intervals and exposed to fog produced by a humidifier. The amount of water harvested by each sample was measured using an ultrasonic fogger. Polypropylene doped with 1% fumed silica was most effective at harvesting water, and collected almost 19–20 times more water than pure polypropylene. This improvement is due to the surface tension, which decreased from 16.754 mN/m (pure PP) to 13.512 and 9.992 mN/m (0.5% and 1% fumed silica, respectively). On the other hand, when fumed silica doping exceeded 1%, this increased the polymer’s surface tension, measured as 20.6 and 38.1 mN/m for 1.5 and 2% fumed silica doping. We therefore propose fog harvesting using 1% fumed silica-doped polypropylene as a low-cost method for collecting clean water in arid regions.

#Materials
Field # Materials
Updated 08 April 2021

#5

 

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Description University commission says anxiety expert pressured whistleblowers over manipulated study data

#Materials
Field # Materials
Updated 08 April 2021

#6

 

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Description TBD

#Materials
Field # Materials
Updated 07 April 2021

#7

 

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Description Time-of-flight secondary ion mass spectrometry fragment analysis remains a challenging task. The fragment appearance regularity (FAR) rule is particularly useful for two-element compounds such as ZnO. Ion fragments appearing in the form of ZnxOy obey the rule $$2x ge 2y + 1$$ in the positive secondary ion spectrum and $$2x le 2y + 1$$ in the negative spectrum where the valence of Zn is + 2 and that of O is − 2. Fragment analysis in gallium-doped ZnO (GZO) films can give insights into the bonding of the elements in this important semiconductor. Fragment analysis of 1 and 7 wt% GZO films shows that only the negative ion fragments obey the FAR rule where ZnO‒, 66ZnO‒, 68ZnO‒ and ZnO2‒ ion fragments appear. In the positive polarity, subdued peaks from out-of-the-rule ZnO+, 66ZnO+ and 68ZnO+ ion fragments are observed. The Ga ion peaks are present in both the positive and negative spectra. The secondary ion spectra of undoped ZnO also shows consistency with the FAR rule. This implies that Ga doping even in amounts that exceed the ZnO lattice limit of solubility does not affect the compliance with the FAR rule.

#Materials
Field # Materials
Updated 07 April 2021

#8

 

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Description In this article, we propose SNG (single negative) metamaterial fabricated on Mg–Zn ferrite-based flexible microwave composites. Firstly, the flexible composites are synthesized by the sol-gel method having four different molecular compositions of MgxZn(1−x)Fe2O4, which are denoted as Mg20, Mg40, Mg60, and Mg80. The structural, morphological, and microwave properties of the synthesized flexible composites are analyzed using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and conventional dielectric assessment kit (DAK) to justify their possible application as dielectric substrate at microwave frequency regime. Thus the average grain size is found from 20 to 24 nm, and the dielectric constants are 6.01, 5.10, 4.19, and 3.28, as well as loss tangents, are 0.002, 0.004, 0.006, and 0.008 for the prepared Mg–Zn ferrites, i.e., Mg20, Mg40, Mg60, and Mg80 respectively. Besides, the prepared low-cost Mg–Zn ferrite composites exhibit high flexibility and lightweight, which makes them a potential candidate as a metamaterial substrate. Furthermore, a single negative (SNG) metamaterial unit cell is fabricated on the prepared, flexible microwave composites, and their essential electromagnetic behaviors are observed. Very good effective medium ratios (EMR) vales are obtained from 14.65 to 18.47, which ensure the compactness of the fabricated prototypes with a physical dimension of 8 × 6.5 mm2. Also, the proposed materials have shown better performances comparing with conventional FR4 and RO4533 materials, and they have covered S-, C-, X-, Ku-, and K-band of microwave frequency region. Thus, the prepared, flexible SNG metamaterials on MgxZn(1−x)Fe2O4 composites are suitable for microwave and flexible technologies.

#Materials
Field # Materials
Updated 07 April 2021

#9

 

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Description TBD

#Materials
Field # Materials
Updated 07 April 2021

#10

 

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Description TBD

#Materials
Field # Materials
Updated 07 April 2021

#11

 

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Description TBD

#Materials
Field # Materials
Updated 07 April 2021

#12

 

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Description Microporous polymers feature shape-persistent free volume elements (FVEs), which are permeated by small molecules and ions when used as membranes for chemical separations, water purification, fuel cells and batteries1–3. Identifying FVEs that have analyte specificity remains a challenge, owing to difficulties in generating polymers with sufficient diversity to enable screening of their properties. Here we describe a diversity-oriented synthetic strategy for microporous polymer membranes to identify candidates featuring FVEs that serve as solvation cages for lithium ions (Li+). This strategy includes diversification of bis(catechol) monomers by Mannich reactions to introduce Li+-coordinating functionality within FVEs, topology-enforcing polymerizations for networking FVEs into different pore architectures, and several on-polymer reactions for diversifying pore geometries and dielectric properties. The most promising candidate membranes featuring ion solvation cages exhibited both higher ionic conductivity and higher cation transference number than control membranes, in which FVEs were aspecific, indicating that conventional bounds for membrane permeability and selectivity for ion transport can be overcome4. These advantages are associated with enhanced Li+ partitioning from the electrolyte when cages are present, higher diffusion barriers for anions within pores, and network-enforced restrictions on Li+ coordination number compared to the bulk electrolyte, which reduces the effective mass of the working ion. Such membranes show promise as anode-stabilizing interlayers in high-voltage lithium metal batteries. A diversity-oriented synthesis approach that yields a library of architecturally broad microporous polymers is used to develop structurally diverse polymer membranes with ion specificity and to screen their properties.

#Materials
Field # Materials
Updated 07 April 2021

#13

 

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Description The use of two-dimensional materials in bulk functional applications requires the ability to fabricate defect-free 2D sheets with large aspect ratios. Despite huge research efforts, current bulk exfoliation methods require a compromise between the quality of the final flakes and their lateral size, restricting the effectiveness of the product. In this work, we describe an intercalation-assisted exfoliation route, which allows the production of high-quality graphene, hexagonal boron nitride, and molybdenum disulfide 2D sheets with average aspect ratios 30 times larger than that obtained via conventional liquid-phase exfoliation. The combination of chlorosulfuric acid intercalation with in situ pyrene sulfonate functionalisation produces a suspension of thin large-area flakes, which are stable in various polar solvents. The described method is simple and requires no special laboratory conditions. We demonstrate that these suspensions can be used for fabrication of laminates and coatings with electrical properties suitable for a number of real-life applications.

#Materials
Field # Materials
Updated 06 April 2021

#14

 

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Description TBD

#Materials
Field # Materials
Updated 06 April 2021

#15

 

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Description Rapidly increasing solar photovoltaic (PV) installations has led to environmental and supply chains concerns. The United States relies on imports of raw materials for solar module manufacturing and imports of PV cells and ...

#Materials
Field # Materials
Updated 05 April 2021