Materials Today最新文献

Inspired by methods of wet fiber spinning, we introduce a process using a 3D printer to create dense carbon nanotube (CNT) fibers and extensible coils with metal-like DC specific conductivity. An extrusion-based printer with an immersed nozzle extrudes a homogeneous shear-thinning ink (with initially < 1 % CNT concentration in water) into a liquid bath of antisolvent, inducing immediate precipitation-driven solidification slightly beyond the nozzle tip. This process forms continuous fibers of CNTs with conductivity up to 3 × 10⁵ S/m, exceeding that of dense graphite and approaching that of CNTs spun from similar inks in a continuous fiber spinning process (6 × 10⁵ S/m). The specific conductivity is up to 1 × 10³ S m²/kg, comparable with gold (2.3 × 10³ S m²/kg). The printing regimes are analyzed, with consideration of the draw ratio imposed during printing. Particular focus is placed on adjusting the speed of counter-diffusion of the ink solvent and the bath liquid, which allows for tuning of fiber diameter, conductivity, and specific conductivity respectively over ranges of one, four, and five orders of magnitude. The conductivity of resulting fibers is maximized when the speed of solvent counter-diffusion is high and the radius reduction is largest. When extrusion speed is also high relative to speed of the nozzle motion, a fluid mechanical coiling instability emerges which creates filaments with periodic coils, allowing for intricate designs to be formed along a linear extrusion path. Once dried, these densely coiled structures initially maintain their shape and can subsequently undergo up to 50 % strain with under 1 % change in resistance and 170 % linear extension with 20 % increase in resistance as the coils unwind. The resulting complex coil structures have applications in lightweight circuitry and as flexible interconnects.

Metal nanoparticles (MNPs) with complex structure and uniform distribution demonstrate interesting physicochemical properties and thus are widely applied. The traditional wet chemistry methods are commonly applied to construct MNPs structure, yet they still exhibit limitations in the liquid-phase environment, particularly, for synthesis of supported MNPs in one-step process. Diverse synthesis strategies have been investigated to design complex MNPs in a more efficient manner, among which the thermal treatment atmosphere induced solid-phase ion diffusion (TASID) synthesis strategy serves as an attractive strategy. This review summaries recent progresses of complex MNPs construction via TASID synthesis strategy, which realize the structure design through thermally treating the precursors under various gas atmosphere, such as oxidative, reductive, carbonaceous, and inert gas. This TASID strategy can both achieve the MNPs structure design and uniform dispersion simultaneously, demonstrating its unique properties. MNPs with diverse composition and structure, such as hollow, core@shell, yolk@shell, Janus, and multi-chamber structure, are successfully synthesized. The TASID synthesis mechanisms of galvanic replacement, Kirkendall effect, Ostwald ripening, carburization, and exsolution are elaborated in detail. The synthesis-mechanism-structure correlation of TASID is identified and the applications of these constructed MNPs are presented. This strategy could be developed into a class of synthetic methods by applying various thermal gas.

Noncovalent π-stacked organic frameworks (πOFs) are a subclass of porous materials that consist of crystalline networks formed by self-assembly of organic building blocks through π-π interactions. Weak intermolecular interactions including π-π interactions have been well studied in the field of supramolecular chemistry and further employed for constructing porous molecular materials. The flexible, reversible, and conductive nature of π-π interactions and π-delocalized supramolecular frameworks impart advantageous attributes to πOFs, including solution processability, self-healing capability, notable carrier mobility and excellent stability. These features make πOFs ideal candidates not only for conventional applications like gas separation, molecular structure determination, and electrocatalysis, but also for endeavors that traditional porous materials can hardly pursue. In this review, we describe the evolution of πOFs chronologically, starting from the development of the π-π interactions model, which has led to the creation of complicated supramolecular architectures and the introduction of the concept of πOFs. Through comparing πOFs with other prevailing porous materials, we highlight their unique aspects of fundamental chemistry and practical advantages. We also summarize the physical properties and applications of πOFs through elucidating the structure–function correlations. Finally, we discuss the design strategies of πOFs that allow for emerging functional applications beyond what traditional porous materials have achieved.

Infants are exceptionally fragile and physically vulnerable who need special healthcare. Continuous monitoring of vital information of infants is essential for understanding their health status. Whereas modern infant health monitoring is carried out with dedicated facilities in controlled hospital settings, they are associated with several issues such as potential iatrogenic injuries, barriers for skin-to-skin parental bonding, and even complications during basic clinical tasks. Recently, soft electronics have become an accessory and mobile infant monitoring platform with remarkable advantages over existing technologies. This review comprehensively summarizes the research advances on soft electronics for advanced infant monitoring. We first introduce the physiological characteristics from anatomy, diseases, and treatments of infants. In accordance with these characteristics, we discuss the progressive achievements of soft bioelectrical, biophysical, biochemical, and hybrid monitoring technologies for infants. In addition, we offer insights into the remaining challenges and future directions of a soft electronics based intelligent system for clinical-grade infant monitoring from sensor design, data processing, power supply, and digital interactions in the era of Internet of Things. Finally, we highlight the translational challenges to be considered in bringing soft electronics for infant monitoring from the benchtop to the bedside.

Eutectic growth process is usually characterized by the simultaneous coupled growth of two different solids within one uniform liquid phase, while fluid dynamics normally predicts the equiaxed shrinkage for floating viscous droplets on freezing. Here a decoupling effect was induced by the microgravity and containerless states aboard space station, which led to the independent dendrite growth of two eutectic phases within extremely undercooled liquid Nb-Si refractory alloy. The confronting fluid flow pattern driven by polar heterogeneous nucleation was found to stimulate the elongated surface deformation of alloy droplet at a high dendrite growth velocity.

Outdoor radiative cooling is a passive method of cooling a surface that faces the sky. During the past decade, numbers of successful demonstrations of daytime radiative coolers have been reported. Because a daytime radiative cooler can be radiatively cooled both during the day and at night, it is always cooled and a temperature difference against the surroundings is generated. This temperature difference can be used to generate thermoelectric power throughout the day by placing a daytime radiative cooler on a thermoelectric module. However, such a device cannot harvest solar heat because sunlight is reflected by the daytime radiative cooler. In this study, a thermoelectric device that simultaneously harvests both radiative cooling and solar heating is presented. The essential component is a vertically placed thermoelectric module made of transparent thermoelectric thin films which allows radiatively cooled and solar heated surfaces to be co-planar. The outdoor and indoor measurements confirm that the device can harvest both radiative cooling and solar heating simultaneously during the day without offsetting each other, and can harvest radiative cooling at night. The co-planar design is an efficient method for simultaneously harvesting solar heating and radiative cooling, which could facilitate efficient energy harvesting and can be applied to a standalone power supply for off-grid sensor modules.

Over the years, reducing friction and wear-induced deformation, damage and/or removal of material at various contact interfaces has always aroused significant interests due to the substantial benefits for impaired machinery components, as well as the efficiencies in energy and economy. Among numerous advanced nanomaterials, carbon nanotubes (CNTs) have been recognized as solid lubricants, or additives in the liquid/solid material systems (coatings, composites and lubricants) to effectively reduce friction and wear. This is well-motivated by CNTs’ hollow tubular nanostructure and outstanding physicochemical properties which can potentially support them with many favorable frictional mechanisms, such as filling/mending effect, sliding/rolling effect, and tribofilm-forming effect. Despite the enormous efforts pertaining to CNTs for tribological optimizations, discussing them across the nano-scale to macro-scale for the understanding of critical interactions between the CNTs and contact objects remains rarely explored. In this review, the state-of-the-art advances in computational tribology research of the CNTs and their significant nano/macro-tribology mechanisms in related systems are methodically provided, beginning with a brief overview of CNTs on their manufacturing, structural properties, and functionalization. Additionally, we present a condensed summary of the encouraging findings, accompanied by some valuable recommendations for the sustaining prosperity of CNTs in tribology.

Convenient, small-sized, and self-powered sensor units are easier to integrate, making them the future development direction of photodetectors. GaN materials with wide band gap are powerful candidates for UV detection, but most GaN based self-powered UV photodetectors have poor detection ability for the weak UV light, which limits their applications. This study reports a self-powered UV photodetector based on BaTiO₃/GaN heterojunction, which can detect ultra-weak UV light at a minimum of 0.68 nW/cm² by coupling the ferroelectric polarization, anti-reflection effect, and pyro-phototronic effect. The polarized BaTiO₃ thin film on the surface of GaN has an enhanced residual polarization field and generated anti-reflection effect, which can regulate the heterojunction band structure, suppress the dark current and minimize surface reflection of GaN. Simultaneously enhanced pyro-phototronic effect can significantly improve the response speed and responsivity of the device. The response time and recovery time of the device are as low as 8.794 ms and 5.018 ms. The maximum responsivity and detectivity are 88.206 mA/W and 7.392 × 10¹³ Jones, respectively, increased by 359% and 6065% compared to the device before polarization. Thanks to excellent material stability, the device has a sensitive and uniform response to continuously incident UV light. In addition, by simulating flame generation, it has been proven that the device has brilliant performance in flame detection and can achieve remote monitoring and fire warning functions. These results can promote the potential application of self-powered UV photodetectors based on BaTiO₃/GaN heterojunction in environmental monitoring and space communication fields.

Contact electrification (CE) is a well-known phenomenon that ubiquitously exists in the charge transfer between solid–solid (S-S) or solid–liquid (S-L) and plays pivotal roles in energy harvesting and self-powered sensing. However, little is known about the CE mechanism during the phase transition. Here, we investigated the mechanism of charge transfer between a representative crystalline ice and a dielectric material during the solid-to-liquid phase transition. This study aimed to determine how the phase transition affects the charge transfer efficiency. Before ice starts melting, electron transfer within S-S contact predominated. As the melted micro-droplets smoothed the rough surface of the ice, the contact area between the materials increased, resulting in a roughly 6-fold enhancement of charge transfer. When the ice melted, droplets condensed on the surface and established S-L contact with the dielectric material. It resulted in the formation of an electrical double layer (EDL) composed of ions and electrons at the contact interface, effectively shielding the surface net charge of the dielectric material and impeding charge transfer between the materials. After the complete melting of ice into water, a stable S-L contact was established, and the EDL formed a stable and strong screening effect, resulting in the lowest level of charge transfer. The findings contributed to enhancing knowledge about interaction and charge transfer between different substances in dynamic phase transition scenarios. It could also provide valuable insights into the optimization and advancement of CE-based triboelectric nanogenerators for energy harvesting and self-powered sensing.

Two-dimensional (2D) van der Waals (vdW) heterostructures offer new platforms for exploring novel physics and diverse applications ranging from electronics and photonics to optoelectronics at the nanoscale. The studies to date have largely focused on transition-metal dichalcogenides (TMDCs) based samples prepared by mechanical exfoliation method, therefore it is of significant interests to study high-quality vdW heterostructures using novel materials prepared by a versatile method. Here, we report a two-step vapor phase growth process for the creation of high-quality vdW heterostructures based on perovskites and TMDCs, such as 2D Cs₃Bi₂I₉/MoSe₂, with a large lattice mismatch. Supported by experimental and theoretical investigations, we discover that the Cs₃Bi₂I₉/MoSe₂ vdW heterostructure possesses hybrid band alignments consisting of type-I and type-II heterojunctions because of the existence of defect energy levels in Cs₃Bi₂I₉. More importantly, we demonstrate that the type-II heterojunction in the Cs₃Bi₂I₉/MoSe₂ vdW heterostructure not only shows a higher interlayer exciton density, but also exhibits a longer interlayer exciton lifetime than traditional 2D TMDCs based type-II heterostructures. We attribute this phenomenon to the reduced overlap of electron and hole wavefunctions caused by the large lattice mismatch. Our work demonstrates that it is possible to directly grow high-quality vdW heterostructures based on entirely different materials which provide promising platforms for exploring novel physics and cutting-edge applications, such as optoelectronics, valleytronics, and high-temperature superfluidity.