液态金属电子输运性质的理论研究

液体的许多重要物理性质及结构稳定性都直接或间接与价电子状态有关,电子输运性质的研究因较直接揭示液体中价电子的变化而倍受重视。主要介绍液态金属电阻率和电势的理论研究现状,分析了获得其中关键参数熔体结构因子及原子间作用势的途径。     

Phoretic Liquid Metal Micro/Nanomotors as Intelligent Filler for Targeted Microwelding

Micro/nanomotors (MNMs) have emerged as active micro/nanoplatforms that can move and perform functions at small scales. Much of their success, however, hinges on the use of functional properties of new materials. Liquid metals (LMs), due to their good electrical conductivity, biocompatibility, and flexibility, have attracted considerable attentions in the fields of flexible electronics, biomedicine, and soft robotics. The design and construction of LM‐based motors is therefore a research topic with tremendous prospects, however current approaches are mostly limited to macroscales. Here, the fabrication of an LM‐MNM (made of Galinstan, a gallium–indium–tin alloy) is reported and its potential application as an on‐demand, self‐targeting welding filler is demonstrated. These LM‐MNMs (as small as a few hundred nanometers) are half‐coated with a thin layer of platinum (Pt) and move in H₂O₂ via self‐electrophoresis. In addition, the LM‐MNMs roaming in a silver nanowire network can move along the nanowires and accumulate at the contact junctions where they become fluidic and achieve junction microwelding at room temperature by reacting with acid vapor. This work presents an intelligent and soft nanorobot capable of repairing circuits by welding at small scales, thus extending the pool of available self‐propelled MNMs and introducing new applications.     

Stretchable and Soft Electronics using Liquid Metals

The use of liquid metals based on gallium for soft and stretchable electronics is discussed. This emerging class of electronics is motivated, in part, by the new opportunities that arise from devices that have mechanical properties similar to those encountered in the human experience, such as skin, tissue, textiles, and clothing. These types of electronics (e.g., wearable or implantable electronics, sensors for soft robotics, e‐skin) must operate during deformation. Liquid metals are compelling materials for these applications because, in principle, they are infinitely deformable while retaining metallic conductivity. Liquid metals have been used for stretchable wires and interconnects, reconfigurable antennas, soft sensors, self‐healing circuits, and conformal electrodes. In contrast to Hg, liquid metals based on gallium have low toxicity and essentially no vapor pressure and are therefore considered safe to handle. Whereas most liquids bead up to minimize surface energy, the presence of a surface oxide on these metals makes it possible to pattern them into useful shapes using a variety of techniques, including fluidic injection and 3D printing. In addition to forming excellent conductors, these metals can be used actively to form memory devices, sensors, and diodes that are completely built from soft materials. The properties of these materials, their applications within soft and stretchable electronics, and future opportunities and challenges are considered.     

An Analytical Equation of State for Some Saturated Liquid Metals

An analytical equation of state (EoS) is developed for some saturated molten metals. The equation is that of Ihm, Song and Mason in which the three temperature–dependent parameters, second virial coefficient, van der Waals co–volume, and a scaling parameter, are calculated by means of corresponding states correlations. The required characteristic constants are the heat of vaporization and the density at the melting point, H _vap and _m, respectively. The EoS is applied to these liquid metals to calculate the density at temperatures higher than their melting points. The results are fairly consistent with experiment, maximum difference less than ±4%.     

Electrochemical Oxidation to Fabricate Micro-Nano-Scale Surface Wrinkling of Liquid Metals

Constructing wrinkled structures on the surface of materials to obtain new functions has broad application prospects. Here a generalized method is reported to fabricate multi-scale and diverse-dimensional oxide wrinkles on liquid metal surfaces by an electrochemical anodization method. The oxide film on the surface of the liquid metal is successfully thickened to hundreds of nanometers by electrochemical anodization, and then the micro-wrinkles with height differences of several hundred nanometers are obtained by the growth stress. It is succeeded in altering the distribution of growth stress by changing the substrate geometry to induce different wrinkle morphologies, such as one-dimensional striped wrinkles and two-dimensional labyrinth wrinkles. Further, radial wrinkles are obtained under the hoop stress induced by the difference in surface tensions. These hierarchical wrinkles of different scales can exist on the liquid metal surface simultaneously. Surface wrinkles of liquid metal may have potential applications in the future for flexible electronics, sensors, displays, and so on.     

液态金属扩散系数的测量方法与理论研究的进展

介绍了液态金属扩散系数的测量方法和理论研究,对比了各种实验方法的优缺点,分析了理论计算对实测结果的偏差原因,并指出了存在的问题和发展方向.     

The Law of Corresponding States and Surface Tension of Liquid Metals

Empirical relationships for the surface tension of liquid metals (LM) are shown to follow from the principle of corresponding states. In order to relate the surface tension of LM to its bulk properties, a formula is derived by scaling with the melting point T _m (0) at the atmospheric pressure, p = 0 and the atomic volume _m (0) at the melting point as macroscopic parameters for scaling and a characterizing the interatomic potential (r)= *(r/a). Correlation rules, derived for the surface tension and its temperature coefficient, are discussed and compared with experimental data.     

Application of High-Speed Laser Polarimetry to Noncontact Detection of Phase Transformations in Metals and Alloys at High Temperatures

A high-speed laser polarimetry technique, developed recently for the measurement of normal spectral emissivity of materials at high temperatures, was used to detect solid–solid and solid–liquid phase transformations in metals and alloys in millisecond-resolution pulse-heating experiments. Experiments were performed where normal spectral emissivity at 633 nm was measured simultaneously with surface radiance temperature, resistance, and/or voltage drop across the specimen. It was observed that a phase transformation, as indicated either by an arrest in the specimen radiance temperature or changes in the resistance and/or voltage drop, generally caused a change in normal spectral emissivity. Experiments were conducted on cobalt, iron, hafnium, titanium, and zirconium to detect solid–solid phase transformations. Similar experiments were also performed on niobium, titanium, and the alloy 85titanium–15molybdenum (mass%) to detect solid–liquid phase transformations (melting).     

Measurement of Density and Structural Short-Range Order of Levitated Liquid Metals

The determination of thermophysical properties and structure of undercooled metallic melts must be accomplished by contactless methods due to the high reactivity of the material. It has been shown that electromagnetic levitation provides high-purity conditions to allow deep undercooling. The density and thermal expansion of a levitated drop can be derived from volume measurements using a charge-coupled device (CCD) camera and a digital image processing system. Combining levitation with extended x-ray absorption fine structure (EXAFS) spectroscopy leads to the possibility of studying the local structure of the liquid in a wide temperature range including the deeply undercooled regime.     

Transient State Machine Enabled from the Colliding and Coalescence of a Swarm of Autonomously Running Liquid Metal Motors

Internally triggered motion of an object owns important potential in diverse application areas ranging from micromachines, actuator or sensor, to self‐assembly of superstructures. A new conceptual liquid metal machine style has been presented here: the transient state machine that can work as either a large size robot, partial running elements, or just divide spontaneously running swarm of tiny motors. According to need, the discrete droplet machines as quickly generated through injecting the stream of a large liquid metal machine can combine back again to the original one. Over the process, each tiny machine just keeps its running, colliding, bouncing, or adhesion states until finally assembling into a single machine. Unlike the commonly encountered rigid machines, such transient state system can be reversible in working shapes. Depending on their surface tension, the autonomously traveling droplet motors can experience bouncing and colliding before undergoing total coalescence, arrested coalescence, or total bounce. This finding would help mold unconventional robot in the sense of transient state machine that could automatically transform among different geometries such as a single or swarm, small or large size, assembling and interaction, etc. It refreshes people's basic understandings on machines, liquid metal materials, fluid mechanics, and micromotors.     

Diverse Morphologies of Self‐Assemblies from Homoditopic 1,18‐Nucleotide‐Appended Bolaamphiphiles: Effects of Nucleobases and Complementary Oligonucleotides

The synthesis of 1,18‐nucleotide‐appended bolaamphiphiles (1 , 2 , 4 , and 6) is reported, in which a 3′‐phosphorylated guanidine, adenosine, thymidine, or cytidine is connected to each end of an octadecamethylene chain. Single‐component self‐assemblies and binary self‐assemblies with the complementary oligonucleotides dC ₂₀ , dT ₂₀ , dA ₂₀ , and dG ₂₀ are studied by atomic force microscopy, powder X‐ray diffraction analysis, temperature‐dependent UV absorption, circular dichroism, and attenuated total‐reflection Fourier‐transform infrared spectroscopy. The single‐component self‐assembly of 1 forms a two‐dimensional sheet, whereas the binary self‐assembly 1 / dC ₂₀ gives helical nanofibers. Non‐helical nanofibers are observed for the single‐component self‐assemblies of 2 and 4 , and helical nanofibers form from the binary self‐assembly 2 / dT ₂₀ . Interestingly, helical nanorod structures are obtained from the binary self‐assembly 4 / dA ₂₀ , and the aligned nanorods form a nematic phase. The single‐component and binary self‐assemblies from 6 give unilamellar vesicles owing to a lack of stacking interaction between the cytosine moieties.     

Superheating of Liquid Alkali Metals

The maximum attainable temperature of superheating and the critical temperature of cesium, rubidium, and potassium are correlated using the generalized van der Waals equation of state. This study shows that the maximum attainable temperatures of superheating for liquid cesium, rubidium, and potassium are 1722, 1802, and 2039 K, respectively. The results of the determination of the maximum attainable temperatures of superheating of liquid cesium, rubidium, and potassium are in agreement with experimental data. The given study establishes that liquid cesium, rubidium, and potassium can be superheated up to temperatures of about 200 K below their critical temperatures of 1924, 2017, and 2280 K, respectively. Moreover, cesium, rubidium, and potassium have been found to obey the single-parameter law of corresponding states, with the maximum attainable reduced temperature of superheating as the thermodynamic similarity parameter.