The evaporation of suspension droplets is the underlying mechanism in many surface-coating and surface-patterning applications. However, the uniformity of the final deposit suffers from the coffee-stain effect caused by contact line pinning. Here, we show that control over particle deposition can be achieved through droplet evaporation on oil-wetted hydrophilic surfaces. We demonstrate by flow visualization, theory, and numerics that the final deposit of the particles is governed by the coupling of the flow field in the evaporating droplet, the movement of its contact line, and the wetting state of the thin film surrounding the droplet. We show that the dynamics of the contact line can be tuned through the addition of a surfactant, thereby controlling the surface energies, which then leads to control over the final particle deposit. We also obtain an analytical expression for the radial velocity profile which reflects the hindering of the evaporation at the rim of the droplet by the nonvolatile oil meniscus, preventing flow toward the contact line, thus suppressing the coffee-stain effect. Finally, we confirm our physical interpretation by numerical simulations that are in qualitative agreement with the experiment.

悬浮液滴的蒸发是许多表面涂层和表面图案化应用程序中的基本机制。然而，最终沉积物的均匀性受到由接触线钉扎引起的咖啡渍作用的影响。在这里，我们表明可以通过油润湿的亲水性表面上的液滴蒸发来实现对颗粒沉积的控制。我们通过流动可视化，理论和数值证明，颗粒的最终沉积受蒸发液滴中流场的耦合，其接触线的移动以及液滴周围薄膜的润湿状态的控制。我们表明，可以通过添加表面活性剂来调整接触线的动力学，从而控制表面能，进而控制最终的颗粒沉积。我们还获得了径向速度曲线的解析表达式，该表达式反映了不挥发油弯月面对液滴边缘蒸发的阻碍，从而防止了流向接触线的流动，从而抑制了咖啡渍的影响。最后，我们通过与实验定性一致的数值模拟确认了我们的物理解释。