Mechanics of soft particle capture using nanofiber networks

Nano-particle capture is a key process in filtration, separation, and biomedical applications. Here we explored the mechanisms of soft particle capture using nanofiber networks. We identified possible states of the capture process, which are defined by their structural and material parameters. By performing numerical analysis, we provided a phase diagram in the parametric space of the network structure and interracial adhesion. The work provides a conceptual model for rational design of synthetic materials in related applications that focus on the protection against or removal of virus, as well as other soft particles.

Investigation on the Formation Mechanism of Double-Layer Vertically Aligned Carbon Nanotube Arrays via Single-Step Chemical Vapour Deposition

The mechanism for the formation of double-layer vertically aligned carbon nanotube arrays(VACNTs) through single-step CVD growth is investigated. The evolution of the structures and defect concentration of the VACNTs are tracked by scanning electron microscopy(SEM) and Raman spectroscopy. During the growth, the catalyst particles are stayed constantly on the substrate. The precipitation of the second CNT layer happens at around 30 min as proved by SEM.During the growth of the first layer, catalyst nanoparticles are deactivated with the accumulation of amorphous carbon coatings on their surfaces, which leads to the termination of the growth of the first layer CNTs. Then, the catalyst particles are reactivated by the hydrogen in the gas flow, leading to the precipitation of the second CNT layer. The growth of the second CNT layer lifts the amorphous carbon coatings on catalyst particles and substrates. The release of mechanical energy by CNTs provides big enough energy to lift up amorphous carbon flakes on catalyst particles and substrates which finally stay at the interfaces of the two layers simulated by finite element analysis. This study sheds light on the termination mechanism of CNTs during CVD process.

Micro- and nano-mechanics in China： A brief review of recent progress and perspectives

The past three decades have witnessed the explosion of nanoscience and technology, where notable research efforts have been made in synthesizing nanomaterials and controlling nanostructures of bulk materials. The uncovered mechanical behaviors of structures and materials with reduced sizes and dimensions pose open questions to the community of mechanicians, which expand the framework of continuum mechanics by advancing the theory, as well as modeling and experimental tools. Researchers in China have been actively involved into this exciting area, making remarkable contributions to the understanding of nanoscale mechanical processes, the development of multi-scale, multi-field modeling and experimental techniques to resolve the processing-microstructures-properties relationship of materials, and the interdisciplinary studies that broaden the subjects of mechanics. This article reviews selected progress made by this community, with the aim to clarify the key concepts, methods and applications of micro-and nano-mechanics, and to outline the perspectives in this fast-evolving field.

Analysis of bending and buckling of pre-twisted beams:A bioinspired study

Twisting chirality is widely observed in artificial and natural materials and structures at different length scales. In this paper, we theoretically investigate the effect of twisting chiral morphology on the mechanical properties of elas- tic beams by using the Timoshenko beam model. Particular attention is paid to the transverse bending and axial buckling of a pre-twisted rectangular beam. The analytical solution is first derived for the deflection of a clamped-free beam under a uniformly or periodically distributed transverse force. The critical buckling condition of the beam subjected to its self- weight and an axial compressive force is further solved. The results show that the twisting morphology can significantly improve the resistance of beams to both transverse bending and axial buckling. This study helps understand some phenomena associated with twisting chirality in nature and provides inspirations for the design of novel devices and structures.

Mechanical buckling induced periodic kinking/stripe microstructures in mechanically peeled graphite fla es from HOPG

Mechanical exfoliation is a widely used method to isolate high quality graphene layers from bulk graphite. In our recent experiments, some ordered microstructures, consisting of a periodic alternation of kinks and stripes, were observed in thin graphite flakes that were mechanically peeled from highly oriented pyrolytic graphite. In this paper, a theoretical model is presented to attribute the formation of such ordered structures to the alternation of two mechanical processes during the exfoliation： （1） peeling of a graphite flake and （2） mechanical buckling of the flake being sub- jected to bending. In this model, the width of the stripes L is determined by thickness h of the flakes, surface energy Y, and critical buckling strain ecr. Using some appropriate values of y and ecr that are within the ranges determined by other inde- pendent experiments and simulations, the predicted relations between the stripe width and the flake thickness agree reason- ably well with our experimental measurements. Conversely, measuring the L-h relations of the periodic microstructures in thin graphite flakes could help determine the critical mechan- ical buckling strain εcr and the interface energy γ.

Mechanical responses of the bio-nano interface: A molecular dynamics study of graphene-coated lipid membrane

Bio-nano interfaces between biological materials and functional nanodevices are of vital importance in relevant energy and information exchange processes, which thus demand an in-depth understanding. One of the critical issues from the application viewpoint is the stability of the bio-nano hybrid under mechanical perturbations. In this work we explore mechanical responses of the interface between lipid bilayer and graphene under hydrostatic coating provides remarkable resistance to the pressure or indentation loads, We find that graphene loads, and the intercalated water layer offers additional protection. These findings are discussed based on molecular dynamics simulation results that elucidate the molecular level mechanisms, which provide a basis for the rational design of bionanotechnology- enabled aoolications such as biomedical devices and nanotheraoeutics.

Heat transport in low-dimensional materials: A review and perspective

Heat transport is a key energetic process in materials and devices. The reduced sample size, low dimension of the problem and the rich spectrum of material imperfections introduce fruitful phenomena at nanoscale. In this review, we summarize recent progresses in the understanding of heat transport process in low-dimensional materials, with focus on the roles of defects, disorder, interfaces, and the quantum- mechanical effect. New physics uncovered from computational simulations, experimental studies, and predictable models will be reviewed, followed by a perspective on open challenges.

Directional Oxygen Functionalization by Defect in Different Metamorphic-Grade Coal-Derived Carbon Materials for Sodium Storage

As the limiting factor for an energy storage technique from lab-scale to industrial-scale,cost means not only the price of raw materials but also the simplicity of processing technics.In this work,the oxygen functionalized carbon materials were obtained from three representative different metamorphic-grade coals,that is,lignite,bitumite,anthracite.Oxygen functional groups like quinones,carboxylic anhydrides,and lactones are easier to form near defects according to the thermogravimetric-mass spectrometry measurements and density functional theory calculation.Considering the highest amount of defects and C=O contained functional groups,the low metamorphic-grade lignite derived carbon exhibits a reversible capacity of 259.7 mA h g^(-1)after 50 cycles at 0.03 A g^(-1),best among these micron sized coal-based carbons.The surface active sites contribute highly stable and majority of sodium storage capacity evidenced by in situ Raman spectra and cyclic voltammetry curves at different scan rates.The coal-based carbon materials in this work offer options for industrial applications of sodium-ion battery anode materials.

Ultra-sensitive graphene strain sensor for sound signal acquisition and recognition

为健全信号获得和识别的一个便携、高精确的传感器从编织的特殊设计的 graphene 的薄电影被制作织物(GWF ) 。在被拉长之上，随机的裂缝的高密度出现在网络，它减少当前的小径，从而增加电阻。因此，这部电影能对人的喉咙作为一个紧张传感器起作用以便测量通过肌肉运动，一个声音是否被生产的讲话。超离频敏感允许由提取声波的签名特征的快速、低频率的讲话采样的实现。在这研究， 26 封英语信，典型汉字和音调的代表性的信号，甚至短语和句子被测试，揭示在电阻的明显、典型的变化。而且， graphene 传感器的电阻变化与预告录下的声音完美地反应了。由把人工智能与数字信号处理相结合，我们期望以后，这个 graphene 传感器将能成功地达成复杂声学的系统和听觉的数据的大数量。

Temperature and velocity dependent friction of a microscale graphite-DLC heterostructure

One of the promising approaches to achieving large scale superlubricity is the use of junctions between existing ultra-flat surface together with superlubric graphite mesas.Here we studied the frictional properties of microscale graphite mesa sliding on the diamond-like carbon,a commercially available material with a ultra-flat surface.The interface is composed of a single crystalline graphene and a diamond-like carbon surface with roughness less than I nm.Using an integrated approach,which includes Argon plasma irradiation of diamond-like carbon surfaces,X-ray photoelectron spectroscopy analysis and Langmuir adsorption modeling,we found that while the velocity dependence of friction follows a thermally activated sliding mechanism,its temperature dependence is due to the desorption of chemical groups upon heating.These observations indicate that the edges have a significant contribution to the friction.Our results highlight potential factors affecting this type of emerging friction junctions and provide a novel approach for tuning their friction properties through ion irradiation.

Interlayer shear strength of single crystalline graphite

Reported values （0.2 MPa-7.0 GPa） of the interlayer shear strength （ISS） of graphite are very dispersed. The main challenge to obtain a reliable value of the ISS using conventional measuring methods was the unavailability of sufficiently large single crystalline graphite. Here we present a novel experimental method to measure the ISS, and obtain the value as -0.14 GPa. Our result can serve as an important basis for understanding mechanical behavior of graphite or graphene-based materials.

Production of Poly（3-hydroxybutyrate-co-3-hydroxyhexanoate） by Recombinant Pseudomonas stutzeri 1317 from Unrelated Carbon Sources

合成生物学诺言将由装配整个小径的分开的模块简化新陈代谢的小径的构造。这为象 polyhydroxyalkanoates (公众房产管理局) 那样的工业产品的微生物引起的生产给新途径。在这研究，(3-hydroxybutyrate-co-3-hydroxyhexanoate )(PHBHHx ) 由 Pseudomonas stutzeri， 1317 从无关的碳采购原料 poly 生产例如葡萄糖， P 的 phaC1-phaZ-phaC2 操纵子。stutzeri 1317 被击倒产生 PHA 缺乏的变异的 P。stutzeri 1317LF。然后，包含 phaCAhAReBRe， phaCAhBReGPp 和 phaCAhPAh 的三个模块被介绍进 P。stutzeri 1317LF 独立。饮料烧瓶结果显示先锋供应和公众房产管理局 synthase 活动是为 P 的 PHBHHx 累积的重要因素。stutzeri 1317LF。而且，从不同的碳资源的 recombinants 的 PHBHHx 累积被执行。最高的 PHBHHx 内容是 23.7%( 由质量) 与 58.6%( 由鼹鼠) 3HB 部分。这些结果为进一步改进 P 的 PHBHHx 累积提供基础。从无关的碳来源的 stutzeri。

Fast and uniform growth of graphene glass using confined-flow chemical vapor deposition and its unique applications

Fast and uniform growth of high-quality graphene on conventional glass is of great importance for practical applications of graphene glass. We report herein a confined-flow chemical vapor deposition （CVD） approach for the high- efficiency fabrication of graphene glass. The key feature of our approach is the fabrication of a 2-4 μm wide gap above the glass substrate, with plenty of stumbling blocks; this gap was found to significantly increase the collision probability of the carbon precursors and reactive fragments between one another and with the glass surface. As a result, the growth rate of graphene glass increased remarkably, together with an improvement in the growth quality and uniformity as compared to those in the conventional gas flow CVD technique. These high-quality graphene glasses exhibited an excellent defogging performance with much higher defogging speed and higher stability compared to those previously reported. The graphene sapphire glass was found to be an ideal substrate for growing uniform and ultra-smooth aluminum nitride thin films without the tedious pre-deposition of a buffer layer. The presented confined- flow CVD approach offers a simple and low-cost route for the mass production of graphene glass, which is believed to promote the practical applications of various graphene glasses.

Tunable seesaw-like 3D capacitive sensor for force and acceleration sensing

To address the resource-competing issue between high sensitivity and wide working range for a stand-alone sensor,development of capacitive sensors with an adjustable gap between two electrodes has been of growing interest.While several approaches have been developed to fabricate tunable capacitive sensors,it remains challenging to achieve,simultaneously,a broad range of tunable sensitivity and working range in a single device.In this work,a 3D capacitive sensor with a seesaw-like shape is designed and fabricated by the controlled compressive buckling assembly,which leverages the mechanically tunable configuration to achieve high-precision force sensing(resolution~5.22 nN)and unprecedented adjustment range(by~33 times)of sensitivity.The mechanical tests under different loading conditions demonstrate the stability and reliability of capacitive sensors.Incorporation of an asymmetric seesaw-like structure design in the capacitive sensor allows the acceleration measurement with a tunable sensitivity.These results suggest simple and low-cost routes to high-performance,tunable 3D capacitive sensors,with diverse potential applications in wearable electronics and biomedical devices.

Morphology-controlled Tantalum Diselenide Structures as Self-optimizing Hydrogen Evolution Catalysts

Metallic layered transition metal dichalcogenides(TMDs)nanomaterials based on Group 5 transition metals are attracting substantial interests as alternative catalysts for hydrogen evolution reaction(HER).However,controllable preparation of tantalum diselenide(TaSe2)remains challenging,which has hindered the exploration on its application in HER.Herein,we develop a facile method named surface-assisted chemical vapor transport(SACVT)for controllable synthesis of TaSe2 plates and nanobelts,by regulating the molar ratio of selenium to tantalum and reaction temperature.Unique quasi-arrays and self-supported structure help TaSe2 nanobelt own more active sites and higher ability of charge transfer,so it is superior to TaSe2 plate in electrocatalytic HER.Interestingly,they both exhibit the ability to optimize their morphologies upon cycling for dramatically improved and robust electrocatalytic performance.The selfoptimized structures can increase the effective active surface by exposing more active sites on the basal-planes and edges,shorten the interlayer electron-transfer pathways at a thinned domain,and accelerate the charge transfer,which mainly derive from high basal-plane activity and weak interaction between layers of metallic TaSe2.This work provides a reliable way for controllable synthesis of different TaSe2 structures,motivating further efforts to explore new high-efficiency catalysts in the large family of metallic TMDs for electrochemical energy conversion.

Control of surface wettability via strain engineering

Reversible control of surface wettability has wide applications in lab-on-chip systems, tunable optical lenses, and microfluidic tools. Using a graphene sheet as a sam- ple material and molecular dynamic simulations, we demon- strate that strain engineering can serve as an effective way to control the surface wettability. The contact angles 0 of water droplets on a graphene vary from 72.5° to 106° under biaxial strains ranging from -10% to 10% that are applied on the graphene layer. For an intrinsic hydrophilic surface （at zero strain）, the variation of 0 upon the applied strains is more sensitive, i.e., from 0° to 74.8°. Overall the cosines of the contact angles exhibit a linear relation with respect to the strains. In light of the inherent dependence of the contact an- gle on liquid-solid interfacial energy, we develop an analytic model to show the cos 0 as a linear function of the adsorption energy Eads of a single water molecule over the substrate sur- face. This model agrees with our molecular dynamic results very well. Together with the linear dependence of Eads on bi- axial strains, we can thus understand the effect of strains on the surface wettability. Thanks to the ease of reversibly ap- plying mechanical strains in micro/nano-electromechanical systems, we believe that strain engineering can be a promis- ing means to achieve the reversibly control of surface wetta- bility.

Microstructural ordering of nanofibers in flow-directed assembly

Fabrication of highly ordered and dense nanofibers assemblies is of key importance for high-performance and multi-functional material and device applications. In this work, we design an experimental approach in silico, where shear flow and solvent evaporation are applied to tune the alignment, overlap of nanofibers, and density of the assemblies. Microscopic dynamics of the process are probed by dissipative particle dynamics simulations, where hydrodynamic and thermal fluctuation effects are fully modeled. We find that microstructural ordering of the assembled nanofibers can be established within a specific range of the Peclet numbers and evaporation rates, while the properties of nanofibers and their interaction are crucial for the local stacking order. The underlying mechanisms are elucidated by considering the competition between hydrodynamic coupling and thermal fluctuation. Based on these understandings, a practical design of flow channels for nanofiber assembly with promising mechanical performance is outlined.

Determination of volumetric elastic moduli of plant leaf cells based on pressure-volume curves

Volumetric elastic modulus （VEM） is an important parameter in biophysics and biomechanics of plants for in particular understanding cell growth. This paper proposes a new relation that can be used for precisely determining VEM. With the aid of this relation, it shows that the exponential approximation of the pressure-volume relationship adopted in most of the literatures in this field may lead to serious errors on VEM.