Department of Engineering Mechanics, Tsinghua University, Beijing 100084, China.
Soft Matter. 2015 Jun 21;11(23):4669-73. doi: 10.1039/c5sm00654f.
We discuss how the stain left after evaporation of a suspension evolves with heating of the glass or plastic on which the liquid has been deposited. Upon increasing the substrate temperature, it is found that the stain gradually changes from the usually observed ring to an "eye" shape, that is, a combination of the thick central stain and the thin outer ring. Both the size and the relative volume of the central stain increase with the substrate temperature. The main mechanism for this phenomenon is proposed to be an enhanced Marangoni recirculation flow on hot substrates. These findings can be exploited to continuously tune the morphology of coffee stains, with potential applications in self-assembly and ink-jet printing.
我们讨论了悬浊液蒸发后留下的污渍在加热玻璃或塑料时如何演变。随着基底温度的升高，我们发现污渍逐渐从通常观察到的环状变为“眼状”，即厚的中心污渍和薄的外环的组合。中心污渍的大小和相对体积都随着基底温度的升高而增加。提出的主要机制是热基底上增强的马拉高尼再循环流动。这些发现可用于连续调整咖啡污渍的形态，在自组装和喷墨打印方面有潜在应用。
