Collaborative Research: Wetting of Liquid Metals on Rough Surfaces

液体在固体表面上的扩散在自然界中无处不在，是许多工业过程的关键方面，如低温焊接，高温钎焊，除冰，有机液体吸收等。例如，在钎焊/焊接的情况下，加工的严格时间安排，结合被连接材料的不同润湿特性和扩散过程中可能出现的温度变化，需要精确控制，这反过来又需要定量预测工具。预测这种复杂流动的主要困难包括：(1)扩散表面的粗糙度，(2)液体/熔体与基底之间的化学反应，以及(3)三线（固体、液体和蒸汽/气体相遇的点轨迹）传播的物理机制模型不充分。该项目将通过以下方式整合实验和建模策略：(i)在具有特征的原始和设计表面上进行实验，并对三线运动进行现场监测和测量；（ii）基于扩散界面（相场）模型的理论和建模进展，能够表示相和化学反应前沿的传播，以及三线运动的扩散性质；（iii）建模和实验的集成。实时监测三线周围微尺度上的扩散将成为研究液锋传播动力学的数据来源。为了实现项目目标，将在一个通用的计算有限元框架内实施反应性和非反应性扩散的相场建模，从而能够研究不同几何形状的各种问题。主要的实验挑战与三重线的快速演变和活性底物的存在有关。所需的时间分辨率将通过开发热级显微镜技术来实现，用于原位监测移动的液体锋和接触角的动态。抑制化学反应将通过在液态金属扩散之前形成金属间化合物来实现。主要的建模挑战包括：(a)将控制非反应模型三线运动的表面扩散动力学实现到有限元框架中以模拟粗糙表面，以及(b)将组合的液气相场和化学反应相场实现到有限元框架中。这项研究的影响将在与工业和自然过程有关的广泛应用中感受到。该研究的变革性质在于，它将导致通过表面改变和选择液体系统和固体基质来有效控制润湿的能力。这将使依赖于液体扩散的工业过程和依赖于润湿的产品的合理设计成为可能。

1235757 / 1234581PI: Sekulic / MesarovicSpreading of liquids over solid surfaces is ubiquitous in nature and is the key aspect of many industrial processes, such as low temperature soldering, high temperature brazing, de-icing, organic liquid imbibing, etc. For example, in the case of brazing/soldering, the tight time scheduling of the processing combined with dissimilar wetting properties of materials being joined and a possible variability of temperature during spreading, require a precise control, which in turn requires quantitative prediction tools. The major difficulties in predicting such a complex flow include: (1) roughness of the spreading surface, (2) chemical reactions between the liquid/melt and the substrate, and, (3) inadequate models of the physical mechanism by which the triple line (a locus of points where solid, liquid and vapor/gas meet) propagates. This project will integrate experimental and modeling strategy through: (i) experiments on characterized virgin and designed surfaces, with in situ monitoring and measurements of the triple line motion, (ii) advances in theory and modeling based on the diffuse interface (phase-field) models, capable of representing propagation of phase- and chemical reaction fronts, as well as the diffusive nature of the triple line motion, and, (iii) integration of modeling and experiments. Real time in situ monitoring of the spreading at the micro scale around the triple line will be the source of data on kinetics of the liquid front propagation. To achieve projects objectives, the phase-field modeling for reactive and non-reactive spreading will be implemented within a versatile computational finite element framework, thus enabling studies of variety of problems with different geometries. The major experimental challenges are related to the fast evolution of the triple line and the presence of reactive substrates. The required time resolution will be achieved by developing hot stage microscopy techniques for in situ monitoring of the moving liquid front and the dynamics of the contact angle. Suppression of a chemical reaction will be accomplished by formation of intermetallics prior to spreading of a liquid metal. The major modeling challenges include: (a) implementation of the surface diffusion kinetics governing the motion of the triple line for the non-reactive model into the finite element framework to model rough surfaces, and, (b) implementation of the combined liquid-gas phase-field and the chemical reaction phase-field into the finite element framework.The impact of this investigation will be felt in a broad set of applications, related to industrial and natural processes. The transformative nature of the research is that it will results in the ability to effectively control wetting by surface alterations and the selection of liquid system and solid substrates. This will enable rational design of industrial processes which depend on liquid spreading, and products whose function depends on wetting.