Phototaxis phenomenon is fundamental and critical for optical manipulation of micro-objects. Here, we report the size-dependent negative or positive phototaxis behaviors for microdroplets containing interfacial energy absorber flying in a laser. The critical diameters for such negative-to-positive turnover are studied through both experiments and simulation with different liquids and absorbers, which establishes the mechanism and reveals the role of both the liquid and the absorber inside the microdroplets. This study offers new insight for the manipulation of the phototaxis behavior of micro-objects, showing potential applications in optical trapping and transporting systems that involve light-microdroplet interactions.

The octopus, as one of the most famous celebrities in bionics, has provided various inspirations for camouflage materials, soft-bodied robots, and flexible grabbers. The miniaturization of such structures will help the development of microrobots, microdelivery of drugs, and surface coating. With the lack of relevant effective preparation approaches, however, the generation of such octopus-like structures with a size of similar to 1 mu m or below is challenging. Here, we develop an approach based on laser-microdroplet interaction for generating an octopus-like structure with a size of similar to 1 mu m. The developed approach uses laser-microdroplet interaction to provide a large driving force of similar to 10(7) Pa at a confined space (<1 mu m), locally crumpling the precursor in the microdroplet. The locally crumpled particles possess both crumpled and uncrumpled structures that resemble an octopus's head and soft body. In the adhesion test, the octopus-like particles exhibit high adhesive properties in air, in water, and on a flexible substrate. In the electrochemical test, the octopus-like particles on flexible electrodes show good electrochemical and adhesive properties under hundreds of bending cycles. Benefiting from the combination of crumpled and uncrumpled morphologies, the created particles with octopus-like microstructure are demonstrated to possess comprehensive performance, exhibiting wide application potentials in the fields of microswimmers, surface coatings, and electrochemistry. Additionally, the method developed in this work has the advantages of concentrated energy in a confined space, displaying prospective potentials in micro- and nanoprocessing.

Soft materials tend to be highly permeable to gases, making it difficult to create stretchable hermetic seals. With the integration of spacers, we demonstrate the use of liquid metals, which show both metallic and fluidic properties, as stretchable hermetic seals. Such soft seals are used in both a stretchable battery and a stretchable heat transfer system that involve volatile fluids, including water and organic fluids. The capacity retention of the battery was ~72.5% after 500 cycles, and the sealed heat transfer system showed an increased thermal conductivity of approximately 309 watts per meter-kelvin while strained and heated. Furthermore, with the incorporation of a signal transmission window, we demonstrated wireless communication through such seals. This work provides a route to create stretchable yet hermetic packaging design solutions for soft devices.

Graphene‐based composites show great potential in the development of lightweight functional devices and systems, and polymers are usually used as binders to enhance the mechanical properties of these composites. Due to the low thermal conductivity of the polymer and the high inherent interfacial thermal resistance between polymer and graphene, however, the developed devices and systems generally possess low thermal conductivity, which seriously limits their further thermal‐related applications. Here, a lightweight two‐phase heat transport device (TPHTD) based on a vapor‐liquid phase transition‐based heat transfer by using a graphene‐based composite material as the casing is generated. The graphene‐based TPHTD has high thermal conductivity of up to 1408 W (mK) −1 and realizes ultra‐high specific thermal conductivity of ≈5600 W (mKg) −1 . This graphene‐based device with lightweight and high heat transfer capacity offers new opportunities for efficient thermal management of compact, portable, or wearable electronic and power systems.

This work presents a bottom-up approach to construct an isotropic network of liquid metal in polymer, and such generated isotropic liquid metal network brings large enhancement on the thermal and electrical conductivity of the composite for 3D thermal management. The building blocks are composed of polymer particles coated with liquid metal. The liquid metal starts to flow and fill the gaps between the polymer particles, and fuses with each other to assemble into a continuous liquid metal network in the polymer matrix under the mechanical load during heating. The continuous filler network provides effective paths for thermal and electrical conduction, and thus enhances the thermal and electrical conductivity of the composites. Using biphasic copper-eutectic gallium indium as the filler, we generated polymer composites with thermal conductivity as high as 32.71 W/m.K (90 vol %; under compression) and electrical conductivity up to 1.18 x 10(6) S/m. Moreover, the measurement of the in plane and cross-plane thermal diffusivity reveals the isotropic enhancement of thermal conductivity in such composites, which may help expand the potential application of these composites in 3D thermal management, flexible electronics, energy conversion and soft robotics.

This paper reports the generation of 3D thermal and electrical conductive graphene network in gallium‐based liquid metal (LM) via a simple one‐step ball‐milling approach. In this work, 2D graphene nanoplates and their derivatives were employed to construct 3D thermal and electrical conductive filler networks. It is demonstrated that the obtained composite exhibits the highest 3D thermal conductivity (44.6 W m −1 K −1 ) among the other gallium‐based LM composites with 2D inorganic nanofillers and distinguished electrical conductivity (8.3 S µ m −1 ) among gallium‐based LM composites at present. The enhanced thermal conductivity and wettability of gallium‐based composite lead to its beneficial usage as thermal interface materials with exquisite texture for LED chip heat dissipation. The electrochemical and magnetic experiments confirm that these LM‐based composites can also be controlled under external electrical or magnetic field, which potentially can help extend their application in external field‐driven systems. The findings of this work offer new insight in designing LM‐based composites with enhanced thermal, electrical, and magnetic properties for a wide range of applications, including thermal management systems, 3D printing, flexible conductors, soft robotic systems, and wearable energy technologies.

Metal matrix composite based ultrathin two-phase heat transport devices with excellent thermal conductivity and low thermal expansion can address heat dissipating issues and thermal expansion mismatch-induced mechanical failures in the high-power-density micro-electronic systems. Due to the difficulties in processing metal matrix composites, however, achieving the fabrication of the ultrathin devices and their reliable integration with semiconductor chips has challenges. The precision machining and surface engineering of composite materials address the difficulties in processing metal matrix composite based ultrathin devices and contribute to reliable welding encapsulation of the chip. Here, we generate an ultrathin (<= 1 mm) metal matrix composite based two-phase heat transport device with low thermal expansion and integrate such device with the gallium nitride chip. The sandwich-structured molybdenum (Mo) copper (Cu) composite, Cu-MoCu-Cu, is used as the casing material of the hermetically welded device. The Mo-Cu based two-phase heat transport device demonstrates an extremely low thermal resistance, which is 95% lower than that of the Cu plate. This device with superior thermal conductivity of 10200 W.m(-1).K-1 enables the stable operation of the high-power-density (7.9 x 10(2) W/cm(2)) gallium nitride micro-chip within the safe operating temperature range (20-175 degrees C). In addition, the Mo-Cu based device also helps reduce the thermal stress generated at the encapsulation interface by 39% compared to Cu cooling plate, and thus mitigates the fatigue risks of the device. This chip-level integration of heat transport system using the metal matrix composite-based ultrathin two-phase heat transport devices offers new opportunities in the integration of high heat dissipation and low-stress encapsulation in compact electronic systems.

Boiling can induce the self-assembly of nanomaterials in nanofluids to generate reliable mi-cro/nanostructures for enhancing boiling heat transfer. The practical applications of most nanofluids in boiling, however, are limited by the poor thermal stability at the boiling point, and improving the ther-mal stability of nanofluids at such high temperature is challenging. Here, we demonstrate that the crum-pled graphene can remain uniformly and stably dispersed within deionized water at the boiling point of 100 ??C due to its highly wrinkled structure, while self-assembling to generate a porous structure on the substrate during boiling. Such porous structure can vary the surface micromorphology, wettability and roughness, which increases the nucleation sites and departure frequency of bubbles, thus effectively en-hancing the critical heat flux and the maximum heat transfer coefficient by 80.7 and 89.1% compared to the pristine copper substrate, respectively. This in situ boiling-induced self-assembly provides a facile and low-cost strategy to achieve high-performance boiling heat transfer for a wide variety of nanomaterials. The crumpled graphene/water nanofluid used can be directly utilized as a phase change working medium in boiling systems to harvest thermal energy and generate clean steam. ?? 2022 Elsevier Ltd. All rights reserved.

随着电子器件向着高集成度、大功率迅速发展,散热已经成为制约其发展的关键问题.热管通过气液相变模式进行散热,是最高效的传热方式之一,被广泛应用于航天、航空、电力电子等重要应用领域.这些应用要求热管在具有高传热性能的同时还能长期服役,而热管腐蚀是影响热管寿命的关键.造成热管腐蚀的原因很多,主要包括热管材料与工质相容性较差、热管内发生的气泡破裂和流体冲刷等.详细介绍了热管存在的腐蚀类型、重要影响因素(工质、温度、气体等),探讨了其相应腐蚀机理和腐蚀防护方法,并列举了典型的热管腐蚀实例.同时指出现有的热管腐蚀研究存在的问题,对该领域以后的发展方向作了展望.

This paper reports an interfacial evaporation-driven approach for self-assembly of a gold nanoparticle (AuNP) film at the interface of liquid/air. We have designed colloidal plasmonic AuNPs capped with different types and surface coverage densities of ligands (i.e. purified and unpurified oleylamine-capped or thiol-protected AuNPs) and studied the impact of surface chemistry on the self-assembly of AuNPs using the optically excited plasmonic heating effect. By employing the extended DerjaguinLandau-Verwey-Overbeek model, the calculated lowest potential energies of the assembled AuNPs capped with purified oleylamine or alkyl thiols are between -1 kBT and -2 kBT, which is close to the room temperature thermal energy and represents a meta-stable assembly, indicating the reversible self-assembly of the AuNP film observed from the experiment. Furthermore, we observed the superheating phenomenon in well-dispersed nanoparticle solution while normal boiling occurred in the solutions with AuNP assemblies. The SERS activity of the as-prepared AuNP film has also been studied using rhodamine 6G as a molecular probe. This work not only provides a new aspect of the boiling phenomena of optically heated colloidal plasmonic nanoparticle solutions, but also provides inspiration for a new approach in designing surface ligands on the nanoparticles to realize reversible self-assembly via interfacial evaporation.

The electronic industry is facing pressing needs for cooling system with high-performance in heat transfer and matched coefficient of thermal expansion (CTE) with the chips. Metal composite materials (MCMs) with low CTE can be used in cooling chips to overcome the thermal expansion mismatch between the cooling substrate and chips. However, low thermal conductivity of MCMs limits their application in electronic cooling systems. Increasing the percentage of components with high thermal conductivity can enhance the thermal conductivity of MCMs, but it often leads to increase CTE as well. Here, we demonstrate that vapor–liquid phase change can improve the heat transfer performance of tungsten-copper (W-Cu) alloy-based MCMs while maintain their low CTEs. Such strategy reduces the maximum temperature and thermal resistance of MCMs, and also allows for heat spreading from concentrated heat source with high power density. The W-Cu alloy-based vapor chamber (VC) has low thermal resistance of 0.38 K/W at 100 W and high lateral thermal conductivity of ~1727 W/(m·K). The W-Cu alloy-based VC can be readily integrated with the chip and heat sink to serve as cooling substrates for dissipating the heat and simultaneously lowering the thermal expansion mismatch by using its high thermal conductivity and low CTE.

Graphene-based films generated on a substrate can modify surface structure and chemistry to enable the improvement in heat transfer capacity for many important boiling-related applications. Current methods for preparing these films, however, require additional processing equipment and involve relatively complex processes. Achieving simple and controllable generation of these films remains a great challenge. In this work, we develop a facile subcooled boiling-induced self-assembly (SBISA) method for generating graphene-based films. We first explore the SBISA mechanism and demonstrate the formation of graphene-based films under the action of a combined force induced by the capillary pressure, structural disjoining pressure, and vapor recoil force. In addition, using the SBISA process, we generate a tunable hybrid graphene oxide (GO)/crumpled graphene (CG) film with mixed wettability. The hybrid GO/CG film enables large performance enhancements for boiling with a 150.0% increase in the critical heat flux (CHF) and a 163.9% increase in the maximum heat transfer coefficient (HTC) over a pristine copper surface. This SBISA strategy provides an alternative approach for fabricating tunable films with a hierarchical structure and mixed wettability on various substrates, and it may also help produce surfaces with different micro/nanostructures for enhancing phase-change-based heat transfer. (C) 2021 The Author(s). Published by Elsevier Ltd.

Electrocatalysts play a critical role in electrochemical catalytic processes. In order to rationally design active and durable electrocatalysts, it is crucial to have a deep understanding on the formation mechanism of the electrocatalysts. With the development of in situ transmission electron microscopy (TEM) techniques, it is possible to observe nanoscale behaviors in real-time to probe the formation of various electrocatalysts. Here, the nucleation, growth, attachment, diffusion, corrosion and other nanoscale dynamics related to the formation of zero-dimensional (0D), one-dimensional (1D), and two-dimensional (2D) nanomaterials are discussed. The current challenges and potential opportunities for in situ techniques towards observation of electrocatalyst formation including high resolution, fast imaging and beam effect are also described.

Films with micro/nanostructures that show high wicking performance are promising in water desalination, atmospheric water harvesting, and thermal energy management systems. Here, we use a facile bubble-induced self-assembly method to directly generate films with a nanoengineered crack-like surface on the substrate during bubble growth when self-dispersible graphene quantum dot (GQD) nanofluid is used as the working medium. The crack-like micro/nanostructure, which is generated due to the thermal stress, enables the GQD film to not only have superior capillary wicking performance but also provide many additional nucleation sites. The film demonstrates enhanced phase change-based heat transfer performance, with a simultaneous enhancement of the critical heat flux and heat transfer coefficient up to 169% and 135% over a smooth substrate, respectively. Additionally, the GQD film with high stability enables a performance improvement in the concentration ratio and electrical efficiency of concentrated photovoltaics in an analytical study, which is promising for high-power thermal energy management applications.