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以亲水性微观粗糙表面上不同几何形貌及分布的微柱阵列为对象, 讨论了液滴在亲水性粗糙表面上的润湿过程以及润湿状态的转变阶段. 从能量角度分别考察了微观粗糙结构几何形貌及分布、微柱几何参数、固体表面亲水性、接触角滞后作用等因素对液滴润湿状态转变的影响规律. 研究发现: 在亲水粗糙表面, 正方形微柱呈正六边形阵列分布时, 液滴更容易形成稳定的Cassie状态, 或者液滴仅发生Cassie状态向中间浸润状态的转变; 与此同时, 减小微柱间距、增大方柱宽度或圆柱直径、增大微柱高度、增强固体表面的亲水性将有利于液滴处于稳定的Cassie状态, 或阻止润湿状态向伪-Wenzel或Wenzel状态转变; 然而, 当液滴处于Cassie状态时, 较小的固-液界面面积分数或减弱固体表面亲水性能均有利于增大液滴的表观接触角, 因此在亲水表面设计粗糙结构时应综合考虑润湿状态稳定性和较大表观接触角两方面因素; 此外, 接触角滞后作用对于液滴状态的稳定性以及疏水性能的实现具有相反作用的影响. 研究结果为液滴在亲水表面获得稳定Cassie状态的粗糙结构设计方法提供了理论依据.
关键词:
亲水表面
微观粗糙结构
表面自由能
润湿状态转变 相似文献
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《物理学报》2017,(4)
表面微结构阵列可用于调控微间隙中液体的流动行为、运动阻力和混合特性等.本文采用石英晶体微天平实验研究了微凹坑和微圆柱阵列以及微结构表面形貌对近壁面层液体运动行为的影响.石英晶体微天平的系统频移和半带宽变化与近壁面层液体的运动行为密切相关,研究显示,表面微凹坑倾向于受限液体的运动,因此微凹坑表面引起的频移绝对值明显大于与其具有相同特征尺寸的微圆柱表面,且均大于光滑表面.粗糙表面结构会明显地增加近壁面区域液体运动的紊乱程度,因此具有粗糙顶部的二级微圆柱表面引起的半带宽变化明显大于与其具有相同特征尺寸的微圆柱表面,且均大于光滑表面.该研究为微流道表面阵列微结构形式的选择提供了实验依据. 相似文献
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具有不同组成和形态的聚合物颗粒近来受到越来越多的关注,它们的表面粗糙度显著影响着其理化性能,尤其在调节生物材料与生物系统间的相互作用中发挥着重要作用.本文设计了一种具有表面可调褶皱结构的聚苯乙烯微球.首先通过微流控装置产生尺寸均一的含有疏水聚合物和助表面活性剂的液滴.在有机溶剂的挥发过程中,不断收缩的液滴出现界面不稳定现象.表面面积自发增大,固化后得到表面具有褶皱的微球.研究结果表明,调节助表面活性剂的浓度以及溶剂挥发速率均可以有效调控微球表面粗糙程度.循环肿瘤细胞捕获实验表明,这种褶皱结构能明显增强细胞黏附力,提高细胞捕获量.以上这些特征表明这种表面褶皱微球将在生物医学分析领域具备良好的应用前景. 相似文献
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结构色在光学伪装等领域具有重要的应用前景,但其存在严重的角度依赖性。提出利用随机微扰表面降低反射光谱角度依赖性的方法;研究了不同微扰特征的粗糙表面结构在不同入射角下的反射光谱;通过有限元法计算了横电波、横磁波的反射光谱特性和能量传播特性,并据此获得了等效自然光的反射光谱和角度依赖规律。分析发现在0°~40°入射角度范围内,平整表面结构的反射光谱峰值移动了34.0 nm,随机微扰表面结构的反射光谱峰值仅移动了10.0 nm,角度依赖特性降低了70.6%,结果表明微扰表面结构对于降低角度依赖性具有显著作用。 相似文献
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This paper studies the roughness effect combining with effects of rarefaction and compressibility by a lattice Boltzmann model for rarefied gas flows at high Knudsen numbers. By discussing the effect of the tangential momentum accommodation coefficient on the rough boundary condition, the lattice Boltzmann simulations of nitrogen and helium flows are performed in a two-dimensional microchannel with rough boundaries. The surface roughness effects in the microchannel on the velocity field, the mass flow rate and the friction coefficient are studied and analysed. Numerical results for the two gases in micro scale show different characteristics from macroscopic flows and demonstrate the feasibility of the lattice Boltzmann model in rarefied gas dynamics. 相似文献
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采用格子Boltzmann方法研究了固体壁面对流体的作用强度与其润湿性的关系,在此基础上进一步模拟了疏水表面微通道内的流体流动,获得了润湿性对疏水表面滑移流动及减阻特性的影响规律,证实了疏水表面表观滑移的存在性并揭示了其产生机理.结果表明,疏水性作用在疏水表面的近壁区诱导了一个低密度层,而表观滑移则发生在低密度层上.表观滑移是疏水表面具有减阻作用的直接原因,减阻效果随滑移长度的增大而增大.对于特定的流体系统,滑移长度是疏水表面的固有属性,仅是壁面润湿性的单一函数,而与流动本身的性质无关. 相似文献
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矿井喷雾降尘是利用水雾使粉尘润湿沉降的过程,考虑到固体与液体间分子作用力,本文采用格子Boltzmann方法对液滴沿固壁铺展的动力学行为进行了数值模拟,结果发现铺展直径及动态接触角随时间呈指数规律,确定了液滴表面张力与铺展最大直径间的关系,固壁润湿性对铺展最大速度值影响较大,这些与物理试验及文献结果符合良好. 进一步考察了疏水性强的固壁,发现当液滴表面张力足够小时,铺展接触角可以在90°以下,与理论公式符合. 研究发现铺展过程中伴随着振荡,且铺展到最大时液膜有回缩趋势.
关键词:
液滴
格子Boltzmann方法
铺展
数值模拟 相似文献
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Investigation of cavitation bubble collapse in hydrophobic concave using the pseudopotential multi-relaxation-time lattice Boltzmann method
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《中国物理 B》2021,(4)
The interaction between cavitation bubble and solid surface is a fundamental topic which is deeply concerned for the utilization or avoidance of cavitation effect.The complexity of this topic is that the cavitation bubble collapse includes many extreme physical phenomena and variability of different solid surface properties.In the present work,the cavitation bubble collapse in hydrophobic concave is studied using the pseudopotential multi-relaxation-time lattice Boltzmann model(MRT-LB).The model is modified by involving the piecewise linear equation of state and improved forcing scheme.The fluid-solid interaction in the model is employed to adjust the wettability of solid surface.Moreover,the validity of the model is verified by comparison with experimental results and grid-independence verification.Finally,the cavitation bubble collapse in a hydrophobic concave is studied by investigating density field,pressure field,collapse time,and jet velocity.The superimposed effect of the surface hydrophobicity and concave geometry is analyzed and explained in the framework of the pseudopotential LBM.The study shows that the hydrophobic concave can enhance cavitation effect by decreasing cavitation threshold,accelerating collapse and increasing jet velocity. 相似文献
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Lack of energy conservation in lattice Boltzmann models leads to unrealistically high values of the bulk viscosity. For this reason, the lattice Boltzmann method remains a computational tool rather than a model of a fluid. A novel lattice Boltzmann model with energy conservation is derived from Boltzmann's kinetic theory. Simulations demonstrate that the new lattice Boltzmann model is the valid approximation of the Boltzmann equation for weakly compressible flows and microflows. 相似文献
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Stability and hydrodynamic behaviors of different lattice Boltzmann models including the lattice Boltzmann equation (LBE), the differential lattice Boltzmann equation (DLBE), the interpolation-supplemented lattice Boltzmann method (ISLBM) and the Taylor series expansion- and least square-based lattice Boltzmann method (TLLBM) are studied in detail. Our work is based on the von Neumann linearized stability analysis under a uniform flow condition. The local stability and hydrodynamic (dissipation) behaviors are studied by solving the evolution operator of the linearized lattice Boltzmann equations numerically. Our investigation shows that the LBE schemes with interpolations, such as DLBE, ISLBM and TLLBM, improve the numerical stability by increasing hyper-viscosities at large wave numbers (small scales). It was found that these interpolated LBE schemes with the upwind interpolations are more stable than those with central interpolations because of much larger hyper-viscosities. 相似文献
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G. Th?mmes J. Becker M. Junk A.K. Vaikuntam D. Kehrwald A. Klar K. Steiner A. Wiegmann 《Journal of computational physics》2009,228(4):1139-1156
We consider the lattice Boltzmann method for immiscible multiphase flow simulations. Classical lattice Boltzmann methods for this problem, e.g. the colour gradient method or the free energy approach, can only be applied when density and viscosity ratios are small. Moreover, they use additional fields defined on the whole domain to describe the different phases and model phase separation by special interactions at each node. In contrast, our approach simulates the flow using a single field and separates the fluid phases by a free moving interface. The scheme is based on the lattice Boltzmann method and uses the level set method to compute the evolution of the interface. To couple the fluid phases, we develop new boundary conditions which realise the macroscopic jump conditions at the interface and incorporate surface tension in the lattice Boltzmann framework. Various simulations are presented to validate the numerical scheme, e.g. two-phase channel flows, the Young–Laplace law for a bubble and viscous fingering in a Hele-Shaw cell. The results show that the method is feasible over a wide range of density and viscosity differences. 相似文献
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Y. H. Zhang R. S. Qin Y. H. Sun R. W. Barber D. R. Emerson 《Journal of statistical physics》2005,121(1-2):257-267
Gas flow in microchannels can often encounter tangential slip motion at the solid surface even under creeping flow conditions.
To simulate low speed gas flows with Knudsen numbers extending into the transition regime, alternative methods to both the
Navier–Stokes and direct simulation Monte Carlo approaches are needed that balance computational efficiency and simulation
accuracy. The lattice Boltzmann method offers an approach that is particularly suitable for mesoscopic simulation where details
of the molecular motion are not required. In this paper, the lattice Boltzmann method has been applied to gas flows with finite
Knudsen number and the tangential momentum accommodation coefficient has been implemented to describe the gas-surface interactions.
For fully-developed channel flows, the results of the present method are in excellent agreement with the analytical slip-flow
solution of the Navier–Stokes equations, which are valid for Knudsen numbers less than 0.1. The present paper demonstrates
that the lattice Boltzmann approach is a promising alternative simulation tool for the design of microfluidic devices. 相似文献
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研究了温盐双扩散系统的多组分格子Boltzmann方法.通过对二维方腔的温盐双扩散系统的数值模拟,检验了方法的可行性及有效性,所得到的结果与差分法结果符合良好,继而将此方法推广到三维,建立了三维温盐双扩散系统的格子Boltzmann方法,对三维方腔双扩散问题进行了模拟和分析,并与差分法模拟的结果进行了比较,结果令人满意.最后,分析了格子Boltzmann方法在模拟双扩散对流问题时存在的局限性.
关键词:
格子Boltzmann方法
温盐双扩散
Boussinesq近似
数值模拟 相似文献
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Pseudopotential multi-relaxation-time lattice Boltzmann model for cavitation bubble collapse with high density ratio
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The dynamics of the cavitation bubble collapse is a fundamental issue for the bubble collapse application and prevention. In the present work, the modified forcing scheme for the pseudopotential multi-relaxation-time lattice Boltzmann model developed by Li Q et al. [ Li Q, Luo K H and Li X J 2013 Phys. Rev. E 87 053301] is adopted to develop a cavitation bubble collapse model. In the respects of coexistence curves and Laplace law verification, the improved pseudopotential multi-relaxation-time lattice Boltzmann model is investigated. It is found that the thermodynamic consistency and surface tension are independent of kinematic viscosity. By homogeneous and heterogeneous cavitation simulation, the ability of the present model to describe the cavitation bubble development as well as the cavitation inception is verified. The bubble collapse between two parallel walls is simulated. The dynamic process of a collapsing bubble is consistent with the results from experiments and simulations by other numerical methods. It is demonstrated that the present pseudopotential multirelaxation-time lattice Boltzmann model is applicable and efficient, and the lattice Boltzmann method is an alternative tool for collapsing bubble modeling. 相似文献