Quang Tran Si Bui, Leong Fong Yew, An Hongjie, Tan Beng Hau, Ohl Claus-Dieter
A*STAR Institute of High Performance Computing, 1 Fusionopolis Way, Connexis, 138632, Singapore.
Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, 637371, Singapore.
Sci Rep. 2016 Aug 4;6:30989. doi: 10.1038/srep30989.
We study heterogeneous condensation growth of water droplets on micron-sized particles resting on a level substrate. Through numerical simulations on equilibrium droplet profiles, we find multiple wetting states towards complete wetting of the particle. Specifically, a partially wetting droplet could undergo a spontaneous transition to complete wetting during condensation growth, for contact angles above a threshold minimum. In addition, we find a competitive wetting behavior between the particle and the substrate, and interestingly, a reversal of the wetting dependence on contact angles during late stages of droplet growth. Using quasi-steady assumption, we simulate a growing droplet under a constant condensation flux, and the results are in good agreement with our experimental observations. As a geometric approximation for particle clusters, we propose and validate a pancake model, and with it, show that a particle cluster has greater wetting tendency compared to a single particle. Together, our results indicate a strong interplay between contact angle, capillarity and geometry during condensation growth.
我们研究了位于水平基底上的微米级颗粒上水滴的异质凝结生长。通过对平衡液滴轮廓的数值模拟，我们发现了朝向颗粒完全润湿的多种润湿状态。具体而言，对于高于阈值最小值的接触角，部分润湿的液滴在凝结生长过程中可能会自发转变为完全润湿。此外，我们发现了颗粒与基底之间的竞争润湿行为，有趣的是，在液滴生长后期，润湿对接触角的依赖性发生了反转。使用准稳态假设，我们模拟了在恒定凝结通量下生长的液滴，结果与我们的实验观察结果高度吻合。作为颗粒团簇的几何近似，我们提出并验证了一个薄饼模型，并用它表明颗粒团簇比单个颗粒具有更大的润湿倾向。总之，我们的结果表明在凝结生长过程中接触角、毛细作用和几何形状之间存在强烈的相互作用。
