对流、扩散和毛细吸引对蒸发液滴中颗粒沉积空间结构的联合作用
Joint effect of advection, diffusion, and capillary attraction on the spatial structure of particle depositions from evaporating droplets
摘要：
一个简化的模型，这使我们能够进行计算机模拟的颗粒在蒸发液滴的接触线钉到亲水性基板的传输。该模型考虑了液滴中的平流、扩散和毛细力对颗粒的吸引。在模拟的基础上，我们分析了环形沉积物内部单个颗粒链形成的物理机制。选择的参数对应于Park和Moon的实验[Langmuir 22，3506（2006）]，其中已经确定了胶体颗粒的环形沉积和蛇形链。环形沉积物是由平流和扩散输运作用形成的。我们发现，紧密包装的颗粒在沉积物中是可能的，如果蒸发时间超过基于扩散的有序的特征时间。我们表明，链形成的蒸发过程结束时，由于毛细吸引力的颗粒在由固定半径，其中的局部液滴的高度是可比的颗粒尺寸的区域内。在蒸发开始时，环形沉积被示出为比固定半径移动更快地扩展。然而，在该过程结束时，固定半径迅速超出环的膨胀的内前部。当固定半径向对称轴移动时，蛇形链就在这个最后阶段形成了。
英文摘要：
A simplified model is developed, which allows us to perform computer simulations of the particles transport in an evaporating droplet with a contact line pinned to a hydrophilic substrate. The model accounts for advection in the droplet, diffusion and particle attraction by capillary forces. On the basis of the simulations, we analyze the physical mechanisms of forming of individual chains of particles inside the annular sediment. The parameters chosen correspond to the experiments of Park and Moon [Langmuir 22, 3506 (2006)], where an annular deposition and snakelike chains of colloid particles have been identified. The annular sediment is formed by advection and diffusion transport. We find that the close packing of the particles in the sediment is possible if the evaporation time exceeds the characteristic time of diffusion-based ordering. We show that the chains are formed by the end of the evaporation process due to capillary attraction of particles in the region bounded by a fixing radius, where the local droplet height is comparable to the particle size. At the beginning of the evaporation, the annular deposition is shown to expand faster than the fixing radius moves. However, by the end of the process, the fixing radius rapidly outreaches the expanding inner front of the ring. The snakelike chains are formed at this final stage when the fixing radius moves toward the symmetry axis.
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