Evaporation-induced flow motion and particle deposition in sessile droplets

静止的蒸发液滴看起来可能是简单的系统，但它们隐藏着令人惊讶的复杂现象。蒸发过程引起内部流动和界面流动，一旦液体消失，这些流动会影响留下的沉积物的形状和分布。一个常见的例子是由蒸发的咖啡液滴形成的特征性环形污渍。液滴内部的蒸发驱动流以及液滴区域内的颗粒分布的控制目前是该领域中的主要技术挑战之一，涉及非常不同的领域，例如光刻、光电子学、油漆、喷墨打印和医疗诊断。本提案的主要目的是了解蒸发的作用-驱动流在固着蒸发液滴的传质问题。在这种情况下，质量传递指的是蒸发液滴内的蒸气排放和颗粒运动。首先，将表征由于温度梯度而出现的界面流的贡献。其次，蒸发质量和蒸发驱动流之间的关系将被确定。最后，将评估粒度、疏水性和电荷对最终存款的影响。实验将使用最先进的3D粒子跟踪方法进行，以系统地测量不同操作条件下的流动和粒子运动。所获得的结果将解决长期讨论的蒸发驱动流对蒸发液滴中颗粒沉积物的作用的争论。

Sessile evaporating droplets might appear simple systems but they hide surprisingly complex phenomena. The evaporation process induces internal and also interfacial flows that influence the shape and distribution of the deposits left behind once the liquid has vanished. A common example is given by the characteristic ring-shaped stain formed by an evaporated droplet of coffee. The control of the evaporation-driven flow inside the droplet as well as the particle distribution within the droplet area is currently one of the major technological challenges in this domain, with implications involving very different fields such as lithography, optoelectronics, paints, inkjet printing and medical diagnosis.The main objective of this proposal is to understand the role of the evaporation-driven flows in the mass transfer problem in sessile evaporating droplets. Mass transfer in this case refers to both vapor emission and particle motion within the evaporating droplet. First, the contribution of the interfacial flows emerging as a consequence of temperature gradients will be characterized. Second, the relationship between evaporated mass and evaporation-driven flow will be determined. Finally, the influence of particle size, hydrophobicity and charge on the final deposit will be evaluated. The experiments will be performed using state-of-the-art 3D particle-tracking-methods to measure systematically the flow and particle motion for the different operating conditions. The results obtained will settle the long-discussed debate on the role of evaporation-driven flow on the particle deposits in evaporating droplets.