Zhang Kai, Ma Liran, Xu Xuefeng, Luo Jianbin, Guo Dan
School of Technology, Beijing Forestry University, Beijing 100083, China.
State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China.
Phys Rev E Stat Nonlin Soft Matter Phys. 2014 Mar;89(3):032404. doi: 10.1103/PhysRevE.89.032404. Epub 2014 Mar 17.
The surface temperature can significantly affect the flow field of drying droplets. Most previous studies assumed a monotonic temperature variation along the droplet surface. However, the present analyses indicate that a nonmonotonic spatial distribution of the surface temperature should occur. Three different patterns of the surface temperature distribution may appear during the evaporation process of liquid droplets: (i) the surface temperature increases monotonically from the center to the edge of the droplet; (ii) the surface temperature exhibits a nonmonotonic spatial distribution along the droplet surface; (iii) the surface temperature decreases monotonically from the center to the edge of the droplet. These surface temperature distributions can be explained by combining the evaporative cooling at the droplet surface and the heat conduction across the substrate and the liquid. Furthermore, a "phase diagram" for the distribution of the surface temperature is introduced and the effect of the spatial temperature distribution along the droplet surface on the flow structure of the droplet is discussed. The results may provide a better understanding of the Marangoni effect of drying droplets and provide a potential way to control evaporation-driven deposition as well as the assembly of colloids and other materials.
表面温度会显著影响干燥液滴的流场。以往大多数研究假定液滴表面温度呈单调变化。然而，目前的分析表明，表面温度应呈现非单调的空间分布。在液滴蒸发过程中可能会出现三种不同的表面温度分布模式：(i) 表面温度从液滴中心到边缘单调升高；(ii) 表面温度沿液滴表面呈现非单调空间分布；(iii) 表面温度从液滴中心到边缘单调降低。这些表面温度分布可以通过结合液滴表面的蒸发冷却以及穿过基底和液体的热传导来解释。此外，引入了表面温度分布的“相图”，并讨论了沿液滴表面的空间温度分布对液滴流动结构的影响。这些结果可能有助于更好地理解干燥液滴的马兰戈尼效应，并为控制蒸发驱动的沉积以及胶体和其他材料的组装提供一种潜在方法。
