A coarse-grained lattice gas model is developed to study pattern forming processes in drying drops containing surfactant. By performing Monte Carlo simulations of the model, the coupled dynamics of surfactant and liquid evaporation and the resulting oscillatory dynamics at the contact line are elucidated. We show that the coupled drop dynamics and the resulting final deposition patterns can be altered by adsorption kinetics. For slow adsorption rates, surfactant molecules recirculate along with colloidal particles and the area covered by the surfactant on the surface grows from the contact line as the initial concentration of the surfactant increases. This leads to coffee-ring patterns with wide rim areas upon drying or to multi-ring patterns depending on the surfactant concentration. For fast adsorption rates, a surfactant skin covers the entire surface area during the early phase of evaporation. This suppresses the coffee ring effect, and uniform patterns are obtained independent of surfactant concentration. The results suggest that the distribution of surfactant on the surface is critical in determining final deposition patterns and that understanding of the skin-forming process of the surfactant on the surface can help in manipulating the delicate pattern forming process of particles in evaporating drops.

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表面活性剂对液滴动力学和沉积模式的影响：晶格气体模型

建立了粗粒晶格气体模型，以研究干燥含有表面活性剂的液滴时的图案形成过程。通过对模型进行蒙特卡洛模拟，阐明了表面活性剂和液体蒸发的耦合动力学以及在接触线上产生的振荡动力学。我们表明，耦合的液滴动力学和最终的沉积模式可以通过吸附动力学改变。对于缓慢的吸附速率，表面活性剂分子与胶体颗粒一起再循环，并且随着表面活性剂初始浓度的增加，表面活性剂在表面上覆盖的面积从接触线开始增大。这导致在干燥时具有宽边缘区域的咖啡环图案或取决于表面活性剂浓度的多环图案。为了加快吸附速度，在蒸发的早期阶段，表面活性剂的皮肤覆盖了整个表面积。这抑制了咖啡环效应，并且获得了与表面活性剂浓度无关的均匀图案。结果表明，表面活性剂在表面上的分布对于确定最终的沉积图案至关重要，并且了解表面活性剂在表面上的形成皮肤的过程可以帮助操纵蒸发液滴中微妙的颗粒形成过程。