Solutal Marangoni flow as the cause of ring stains from drying salty colloidal drops
Solutal Marangoni flow as the cause of ring stains from drying salty colloidal drops
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DOI：
10.1103/physrevfluids.4.041601
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发表时间：
2019-04-29
影响因子：
2.7
通讯作者：
Rodriguez Valverde, Miguel A.
中科院分区：
文献类型：
--
作者：
Marin, Alvaro;Karpitschka, Stefan;Rodriguez Valverde, Miguel A.
蒸发的咸水滴在自然界中无处不在，在我们的家中和实验室中都是如此。有趣的是，这种明显简单的系统中的传输过程与蒸发“淡水”液滴的过程有很大的不同，因为对流在一定程度上是由于Marangoni应力而逆转的。这种影响对盐结晶过程和遗留下来的沉积物都有至关重要的后果。在这项工作中，我们展示了前所未有的测量，不仅清楚地证实了流动反转，而且阐明了它们对非挥发溶质分布的影响。与文献中经常报道的相反，这种流动反转并不能防止环状污渍的形成：颗粒仅由界面流动驱动在接触线上积累。因此，我们可以得出结论，经典的“咖啡污渍效应”并不是蒸发液滴中产生环状污渍的唯一机制。
Evaporating salty droplets are ubiquitous in nature, in our home and in the laboratory. Interestingly, the transport processes in such apparently simple systems differ strongly from evaporating "freshwater" droplets since convection is partly inverted due to Marangoni stresses. Such an effect has crucial consequences to the salt crystallization process and to the deposits left behind. In this work we show unprecedented measurements that, not only confirm clearly the flow inversion, but also elucidate their impact on the distribution of nonvolatile solutes. Contrary to what has been often reported in the literature, such a flow reversal does not prevent the formation of ring-shaped stains: particles accumulate at the contact line driven solely by the interfacial flow. We can therefore conclude that the classical "coffee-stain effect" is not the only mechanism that can generate ring-shaped stains in evaporating droplets.