Xie Qingguang, Harting Jens
Department of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600MB Eindhoven, The Netherlands.
Soft Matter. 2019 Aug 28;15(32):6461-6468. doi: 10.1039/c9sm01048c. Epub 2019 Jul 11.
Droplets on a liquid-immersed solid surface are key elements in many applications, such as high-throughput chemical analysis and droplet-templated porous materials. Such surface droplets dissolve when the surrounding liquid is undersaturated and the dissolution process is usually treated analogous to a sessile droplet evaporating in air. Typically, theoretical models predict the mass loss rate of dissolving droplets as a function of droplet geometrical factors (radius, constant angle), and droplet material properties (diffusion constant and densities), where the thickness of the surrounding liquid layer is neglected. Here, we investigate, both numerically and theoretically, the effect of the liquid layer thickness on the dissolution of surface droplets. We perform 3D lattice Boltzmann simulations and obtain the density distribution and time evolution of droplet height during dissolution. Moreover, we find that the dissolution slows down and the lifetime linearly increases with increasing the liquid layer thickness. We propose a theoretical model based on a quasistatic diffusion equation which agrees quantitatively with simulation results for thick liquid layers. Our results offer insight to the fundamental understanding of dissolving surface droplets and can provide valuable guidelines for the design of devices where the droplet lifetime is of importance.
浸没在液体中的固体表面上的液滴是许多应用中的关键要素，例如高通量化学分析和液滴模板化多孔材料。当周围液体不饱和时，此类表面液滴会溶解，并且溶解过程通常被视为类似于在空气中蒸发的静止液滴。通常，理论模型将溶解液滴的质量损失率预测为液滴几何因素（半径、恒定角度）和液滴材料特性（扩散常数和密度）的函数，其中忽略了周围液体层的厚度。在此，我们通过数值和理论方法研究了液体层厚度对表面液滴溶解的影响。我们进行了三维格子玻尔兹曼模拟，并获得了溶解过程中液滴高度的密度分布和时间演化。此外，我们发现随着液体层厚度的增加，溶解速度减慢且寿命呈线性增加。我们基于准静态扩散方程提出了一个理论模型，该模型与厚液体层的模拟结果在数量上一致。我们的结果为深入理解溶解的表面液滴提供了见解，并可为液滴寿命至关重要的设备设计提供有价值的指导。
