Theoretical optimization of micropillar arrays for structurally stable bioinspired dry adhesives

Inspired by the excellent adhesion performances of setae structure from organisms,micro/nano-pillar array has become one of the paradigms for adhesive surfaces.The micropillar arrays are composed of the resin pillars for adhesion and the substrate with different elastic modulus for supporting.The stress singularity at the bi-material corner between the pillars and the substrate can induce the failure of the micropillar-substrate corner and further hinder the fabrication and application of micropillar arrays,yet the design for the stability of the micropillar array lacks systematical and quantitative guides.In this work,we develop a semi-analytical method to provide the full expressions for the stress distribution within the bi-material corner combining analytical derivations and numerical calculations.The predictions for the stress within the singularity field can be obtained based on the full expressions of the stress.The good agreement between the predictions and the FEM results demonstrates the high reliability of our method.By adopting the strain energy density factor approach,the stability of the pillar-substrate corner is assessed by predicting the failure at the corner.For the elastic mismatch between the pillar and substrate given in this paper,the stability can be improved by increasing the ratio of the shear modulus of the substrate to that of the micropillar.Our study provides accurate predictions for the stress distribution at the bi-material corner and can guide the optimization of material combinations of the pillars and the substrate for more stable bioinspired dry adhesives.

A review of challenges and opportunities in micropillar compression studies in Mg alloys

This review paper provides an overview of the micropillar compression technique as applied to magnesium(Mg) and its alloys. It explores the influence of various factors, such as pillar size, shape, temperature, and strain rate on the mechanical properties of Mg.Additionally, the impact of alloying elements, aging, and precipitates in Mg alloys has been extensively examined, revealing their significant influence on mechanical performance. The study highlights the strength and strain hardening improvements in Mg with decreasing pillar size in micropillar compression. Furthermore, the role of precipitates as strengthening agents, affecting deformation mechanisms and overall mechanical response, is explored. These valuable insights are crucial for designing Mg-based materials with enhanced mechanical properties for advanced engineering applications.

Silicon micropillar electrodes of lithiumion batteries used for characterizing electrolyte additives

The 100 crystal-oriented silicon micropillar array platforms were prepared by microfabrication processes for the purpose of electrolyte additive identification. The silicon micropillar array platform was used for the study of fluorinated vinyl carbonate(FEC), vinyl ethylene carbonate(VEC), ethylene sulfite(ES), and vinyl carbonate(VC) electrolyte additives in the LiPF_6 dissolved in a mixture of ethylene carbonate and diethyl carbonate electrolyte system using charge/discharge cycles, electrochemical impedance spectroscopy, cyclic voltammetry, scanning electron microscopy, and x-ray photoelectron spectroscopy. The results show that the silicon pillar morphology displays cross-shaped expansion after lithiation/delithiation, the inorganic lithium salt keeps the silicon pillar morphology intact, and the organic lithium salt content promotes a rougher silicon pillar surface. The presence of poly-(VC) components on the surface of FEC and VC electrodes allows the silicon pillar to accommodate greater volume expansion while remaining intact. This work provides a standard, fast, and effective test method for the performance analysis of electrolyte additives and provides guidance for the development of new electrolyte additives.

Micropillar Cavity Design for 1.55-μm Quantum-Dot Single-Photon Sources

The 1.55-μm quantum-dot (QD) micropillar cavities are strongly required as single photon sources (SPSs) for silica-fiber-based quantum information processing. Theoretical analysis shows that the adiabatic distributed Bragg reflector (DBR) structure may greatly improve the quality of a micropillar cavity. An InGaAsP/InP micropillar cavity is originally difficult, but it becomes more likely usable with inserted tapered (thickness decreased towards the center) distributed DBRs. Simulation turns out that, incorporating adiabatically tapered DBRs, a Si/SiO2- InP hybrid micropillar cavity, which enables weakly coupling InAs/InP quantum dots (QDs), can even well satisfy strong coupling at a smaller diameter. Certainly, not only the tapered structure, other adiabatic designs, e.g., both DBR layers getting thicker and one thicker one thinner, also improve the quality, reduce the diameter, and degrade the fabrication difficulty of Si/SiO2-InP hybrid micropillar cavities. Furthermore, the problem of the thin epitaxial semiconductor layer can also be greatly resolved by inserting adiabatic InGaAsP/InP DBRs. With tapered DBRs, the InGaAsP/InP-air-aperture micro-pillar cavity serves as an efficient, coherent, and monolithically producible 1.55-μm single-photon source (SPS). The adiabatic design is thus an effective way to obtain prospective candidates for 1.55-μm QD SPSs.

Dissipative particle dynamics simulation of flow through periodic arrays of circular micropillar

Flow through arrays of micropillar embedded inside microfluidic chip systems is important for various microfluidic devices. It is critical to accurately predict the mass flow rate through pillar arrays based on the pillar design. This work presents a dissipative particle dynamics （DPD） model to simulate a problem of flow across periodic arrays of circular micropillar and investigates the permeability of two types of micropillar arrays. The flow fields including horizontal and vertical velocity fields, the number density field, and the streamline of the flow are analyzed. The predicted solid volumes by the presented DPD simulation of both types of arrays are quite close to the actual counterparts. These quantitative agreements show usefulness and effectiveness of the DPD model in simulating arrays of micropillar. By comparing two types of micropillar arrangement patterns, we find that the arrangement pattern of micropillar does not have significant influence on the permeability of the array.

Magnetized Micropillar-Enabled Wearable Sensors for Touchless and Intelligent Information Communication

The wearable sensors have recently attracted considerable attentions as communication interfaces through the information perception,decoding,and conveying process.However,it is still challenging to obtain a sensor that can convert detectable signals into multiple outputs for convenient,e cient,cryptic,and high-capacity information transmission.Herein,we present a capacitive sensor of magnetic field based on a tilted flexible micromagnet array(t-FMA)as the proposed interaction interface.With the bidirectional bending capability of t-FMA actuated by magnetic torque,the sensor can recognize both the magnitude and orientation of magnetic field in real time with non-overlapping capacitance signals.The optimized sensor exhibits the high sensitivity of over 1.3 T-1 and detection limit down to 1 mT with excellent durability.As a proof of concept,the sensor has been successfully demonstrated for convenient,e cient,and programmable interaction systems,e.g.,touchless Morse code and Braille communication.The distinguishable recognition of the magnetic field orientation and magnitude further enables the sensor unit as a high-capacity transmitter for cryptic information interaction(e.g.,encoded ID recognition)and multi-control instruction outputting.We believe that the proposed magnetic field sensor can open up a potential avenue for future applications including information communication,virtual reality device,and interactive robotics.

A shape-reconfigurable,light and magnetic dual-responsive shape-memory micropillar array chip for droplet manipulation

Droplet manipulation on an open surface has great potential in chemical analysis and biomedicine engineering.However,most of the reported platforms designed for the manipulation of water droplets cannot thoroughly solve the problem of droplet evaporation.Herein,we report a shape-reconfigurable micropillar array chip for the manipulation of water droplets,oil droplets and water-in-oil droplets.Water-in-oil droplets provide an enclosed space for water droplets,preventing the evaporation in an open environment.Perfluoropolyether coated on the surface of the chip effectively reduces the droplet movement resistance.The micropillar array chip has light and magnetic dual-response due to the Fe3O4 nanoparticles and the reduced iron powder mixed in the shape-memory polymer.The micropillars irradiated by a near-infrared laser bend under the magnetic force,while the unirradiated micropillars still keep their original shape.In the absence of a magnetic field,when the micropillars in a temporary shape are irradiated by the near-infrared laser to the transition temperature,the micropillars return to their initial shape.In this process,the surface morphology gradient caused by the deformation of the micropillars and the surface tension gradient caused by the temperature change jointly produce the driving force of droplet movement.

Reveal Hydrogen Behavior at Grain Boundaries in Fe-22Mn-0.6C TWIP Steel via In Situ Micropillar Compression Test

In this study,the effect of hydrogen on dislocation and twinning behavior along various grain boundaries in a high-manganese twinning-induced plasticity steel was investigated using an in situ micropillar compression test.The compressive stress in both elastic and plastic regimes was increased with the presence of hydrogen.Further investigation by transmission electron backscatter diffraction and scanning transmission electron microscope demonstrated that hydrogen promoted both dislocation multiplication and twin formation,which resulted in higher stress concentration at twin-twin and twin-grain boundary intersections.

Molecular dynamics simulation and micropillar compression of deformation behavior in iridium single crystals

The compression behaviors of iridium single crystals with different crystalline orientations were investigated by micropillar compression tests and molecular dynamics(MD) simulations.The results indicated that the deformation process of iridium single crystals with [100]and [110] orientations was presented as the stacking faults expansion and the formation of Lomer-Cottrell locks.And the occurrence of Lomer-Cottrell locks was considered as the interaction of stacking faults on {111} planes by MD simulations.The evolution of crystal structure in compression indicated that the Lomer-Cottrell locks might contribute to the large plastic deformation of iridium single crystals.Moreover,the deformation features in MD simulations showed that the elastic modulus(E) and yield stress(σ_(s)) of iridium single crystals were significantly influenced by the temperature.The elastic modulus and yield stress gradually decreased with an increased temperature for all orientations.Meanwhile,the single crystal with a closely spaced lattice structure exhibited superior mechanical properties at a same temperature.

硅基微柱簇阵列微通道流动沸腾实验研究

为实现硅基微通道流动沸腾换热强化,分别设计并加工了具有并联微通道、稀疏微柱簇和致密微柱簇结构的微通道换热器,以丙酮为工质开展热通量200~650 kW·m^(-2)的流动沸腾实验。结果表明,相较于并联微通道,稀疏微柱簇和致密微柱簇微通道具有更强的两相换热性能;在质量流速43 kg·m^(-2)·s^(-1)的条件下,稀疏微柱簇微通道与致密微柱簇微通道的平均传热系数分别可达到18.6和17.8 kW·m^(-2)·K^(-1),稀疏微柱簇微通道PEC最大可达到1.49。微柱簇阵列随热通量的增加呈现出三种不同流型,可视化研究表明,稀疏微柱簇内产生的汽相更倾向发生微柱簇绕流,而致密微柱簇内产生的汽相更倾向包裹住微柱簇,这使得前者表现出更强的两相换热性能。

柔性微结构生物电干电极研究进展

为探讨柔性微结构生物电干电极的研究进展,结合国内外最新的研究成果,介绍了微结构生物电干电极的表面接触式和穿透接触式两种工作原理及各自简化的界面模型和等效电路模型。基于微针结构、微柱结构和微褶皱结构的不同特点,将微结构干电极分为微针干电极、微柱干电极和微褶皱干电极,分别从电极所使用的基底和导电材料、电极制备工艺技术、仿生结构的运用和生物电信号采集性能等方面进行了详细的综述。最后分析了三种微结构生物电干电极在长期动态生物电信号的监测方面存在的优缺点,并对该领域未来的发展趋势和研究重点进行了展望。

基于微柱阵列的ZnO纳米线的微流控合成

开发了一种新型的微流控合成方法,通过微通道内周期性排列的微柱阵列调节微通道内的局域流场,实现了连续流微环境下氧化锌(ZnO)纳米线的可控合成。分析了微柱阵列中行间距和列间距变化对通道内剪切流场的影响,研究了局域流场的变化对纳米线形貌和尺寸的影响。随着行间距的不断减小或列间距的不断增大,柱间区C1的局域流场不断增大,纳米线的直径与长度也随之增大。以异硫氰酸荧光素标记的羊抗牛免疫球蛋白G(FITC-antiIgG)为模型分子,对ZnO纳米线在生物荧光检测中的应用进行了探究。结果表明,行间距为200μm、列间距为200μm微柱阵列的芯片中制备的纳米线具有最大的表面积,表现出最佳的荧光增强性能。

The metastable constituent effects on size-dependent deformation behavior of nanolaminated micropillars: Cu/FeCoCrNi vs Cu/CuZr

Metastable high entropy alloys(HEAs) and amorphous metallic glasses(MGs), with the chemical disordered character, are intensively studied due to their excellent performance. Here, we introduce Cu to separately constrain these two metastable materials and comparatively investigate their deformation behaviors and mechanical properties of Cu/HEA Fe Co Cr Ni and Cu/MG Cu Zr nanolaminated micropillars in terms of intrinsic layer thickness h and extrinsic pillar diameter D. The metastable HEA layers, as the hard phase in Cu/HEA micropillars, are stable and dominate the deformation, while transformation(crystallization) occurs in MG which plays a minor role in deformation of Cu/MG micropillars. The h-controlled deformation mode transits from the D-independent homogenous-like deformation at large h to the Ddependent shear banding at small h in both Cu/HEA and Cu/MG micropillars. Although both Cu/HEA and Cu/MG micropillars exhibit a maximum strain hardening capability controlled by h, the former manifests much lower hardening capability compared with the latter. The intrinsic size h and extrinsic size D have a strong coupling effect on the strength of Cu/HEA and Cu/MG micropillars. The strength of strength of Cu/HEA micropillars exhibits the D-dependent transition from "smaller is stronger" to "smaller is weaker"with increasing h. By contrast, the strength of Cu/MG micropillars exhibits the transition from bulk-like D-independent behavior at large h to small volume D-dependent behavior(smaller is stronger) at small h.

Effect of hydrogen on deformation behavior of Alloy 725 revealed by in-situ bi-crystalline micropillar compression test

Nickel-based Alloy 725 bi-crystalline micropillars with different types of grain boundaries(GBs)were compressed in hydrogen-free and in-situ hydrogen-charged conditions to investigate the hydrogen effect on the deformation behavior of the selected GBs.In the presence of hydrogen,the compressive stresses on the micropillars increase regardless of the GB type.It was proposed that this hydrogen-induced hardening behavior is the synergistic effect of hydrogen-enhanced dislocation multiplication and interactions,the pinning effect of hydrogen on dislocation motion,and hydrogen-enhanced lattice friction.Transmission electron backscatter diffraction(t-EBSD)results demonstrate that both low-angle GBs and high-angle GBs can effectively suppress dislocation transmission through the GBs,resulting in dislocations pile up along the GBs in the hydrogen-charged condition.In contrast,this behavior was not observed in the micropillars with twin boundaries.

Dynamic recrystallization-induced temperature insensitivity of yield stress in single-crystal Al1.2CrFeCoNi micropillars

High-entropy alloys, a new class of metallic materials, exhibit excellent mechanical properties at high temperatures. In spite of the worldwide interest, the underlying mechanisms for temperature dependence of mechanical properties of these alloys remain poorly understood. Here, we systemically investigate the mechanical behaviors and properties of Al_(1.2)CrFeCoNi(comprising a body-centered cubic phase) and Al_(0.3)CrFeCoNi(comprising a face-centered cubic phase) single-crystal micropillars with three orientations([100], [110], and [111]) at temperatures varying from 300 to 675 K by using in situ compression of micropillars inside a scanning electron microscope. The results show that the yield stresses of Al_(1.2)CrFeCoNi micropillars are insensitive to temperature changes, and their flow stresses and work hardening rates increase slightly with increasing temperature from 300 to550 K, which differs from the typical temperature dependence of yield/flow stresses in metals and alloys. In contrast,Al_(0.3)CrFeCoNi micropillars exhibit typical thermal softening. Furthermore, it is found that the Al_(1.2)CrFeCoNi micropillars exhibit a transition from homogenous deformation to localized deformation at a critical temperature, while the Al_(0.3)CrFeCoNi micropillars always maintain a well-distributed and fine slip deformation. Detailed transmission electron microscopy analyses reveal that dynamic recrystallization(involving dislocation tangles, and formation of dislocation cell structures and sub-grains)plays a key role in the observed temperature insensitivity of the yield stress and increasing flow stress(and work hardening rate)with increasing temperature in the Al_(1.2)CrFeCoNi micropillars, and that thermally activated dislocation slip leads to thermal softening of the Al_(0.3)CrFeCoNi micropillars. The differences in deformation modes and temperature dependence of the mechanical properties between Al_(1.2)CrFeCoNi and Al_(0.3)CrFeCoNi essentially originate from the differences in dislocation activities and slip systems since the two alloys adopt different phases. Our findings provide key insights in the temperature dependence of mechanical properties and deformation behaviors of high-entropy alloys with body-centered cubic and face-centered cubic phases.

限量供油条件下微柱阵列束油表面润滑增效特性研究

在润滑轨道两侧制备以防指纹油涂层(Anti-fingerprint coating,AFC)修饰的微柱阵列(Micropillar array,MA),形成润湿性梯度束油的润滑增效表面.使用点接触光弹流润滑油膜测量仪测量了该表面在限量供油往复运动条件下的油膜厚度以及油池形态,探究了往复频率、束油轨道宽度和载荷对润滑性能的影响,同时与未经AFC修饰的微柱阵列束油表面和仅以AFC形成的束油表面进行了对比.结果表明:制备的经AFC修饰的微柱阵列束油表面比其他2个束油表面有更好的润滑特性,往复运动条件(4 Hz)下明显改善了行程中点及两端点处的润滑状态,相对原始未处理表面行程中点处中心油膜厚度最高提升了51.4%.表面在束油轨道宽度接近Hertz接触区宽度时集油效果最强,随着轨道宽度增加集油效果减弱.载荷对微柱束油阵列表面的集油效果影响显著,随着载荷增大轨道机械分离作用变强、毛细回流作用减弱,造成集油能力和油膜厚度下降.

用于细胞三维培养的集成微柱阵列的微流控芯片设计与验证

设计并验证了一种用于细胞三维培养的集成微柱阵列的微流控芯片。芯片由一片聚二甲基硅氧烷(PDMS)沟道片和一片玻璃盖片组成,在PDMS沟道片上集成了一个由两排微柱阵列围成的细胞培养室和两条用于输送培养基的侧沟道。微柱间距直接影响了芯片的使用性能,是整个芯片设计的关键。基于数值模拟和实验验证,本研究对微柱间距进行了优化设计。优化后的微流控芯片可以很好地实现细胞与细胞外基质模拟材料混合液的稳定注入、培养基中营养物质向培养室内的快速扩散和细胞代谢物的及时排出。在芯片上进行了神经干细胞的三维培养,证明了芯片上构建的细胞体外微环境的稳定性。

W/O液滴绕流微柱阵列的数值模拟研究

基于COMSOL Multiphysics 4.1层流两相流模型,通过数值模拟研究了连续相流速一定的情况下大接触角(?=160°)的油包水(W/O)液滴绕流微柱阵列的二维运动。通过相场方法考虑表面张力的影响,实现对油-水界面的追踪,获得了W/O液滴的运动状态,重点考查了液滴尺寸对运动特性的影响。模拟结果表明,初始尺寸不同的液滴变形后,长度上存在差异,但厚度基本一致,尺寸介于100?m^150?m液滴的运动速度与液滴尺寸无关。进一步研究了利用尖楔对液滴进行分割的过程,发现液滴脱离末端微柱时,其垂向位置高度与液滴尺寸密切相关,呈先线性增加后趋于定值的特点,利用这一预定位功能及尖楔结构可以获得尺寸可控的均匀子液滴。数值方法与已有实验结果基本一致,且可以很好地表现W/O液滴与微柱的相互作用,揭示液滴的流动细节和运动规律,为设计更为复杂的液滴微流控芯片提供了支撑。

基于应变梯度晶体塑性理论的金属微柱轴向压缩有限元分析

微压缩实验研究发现,随着微柱直径减小,以剪切带形式表征的非均匀塑性变形会愈加明显。为了考察应变梯度对微柱塑性行为的影响,构建了一种适用于切线模量算法的低阶应变梯度理论模型。该模型提出了包含塑性应变与应变梯度的塑性硬化模量表达式,建立了应变梯度增量与剪切应变增量之间的线性显式关系。通过对上述模型进行有限元实现,模拟了Ni单晶微柱的轴向压缩过程,并将预测结果与一种基于向前欧拉算法的低阶应变梯度塑性模型计算结果进行了比较,检验了理论模型的合理性与算法的可靠性。研究表明,Ni微柱在轴向压缩过程中产生的应变梯度,能够较为显著地提高塑性变形过程中的应变硬化率。

微柱萃取与高效液相色谱联用测定镇定剂残留

环境水和血液样品中镇静剂残留浓度低,且基质复杂,干扰严重,需经高效样品前处理技术对目标物进行富集分离。采用C_(18)微柱离心萃取解吸的新型微萃取模式,与高效液相色谱联用,建立了环境水和血样中三唑仑、安定和唑吡坦3种镇静剂残留的分析方法。研究结果表明,NaCl浓度为0.35 g/mL条件下萃取效果最佳。在最佳条件下,3种镇定剂在20～200μg/L范围内与峰面积呈良好的线性关系,相关系数均大于0.99。三唑仑、安定和唑吡坦的检出限分别为2.51μg/L,2.67μg/L和3.36μg/L。用于河水和血液样品中镇定剂残留测定,平均加标回收率高于84%。