Spatiotemporal measurement of surfactant distribution on gravity–capillary waves

Materials adsorbed onto the surface of a fluid – for instance, crude oil, biogenic slicks or industrial/medical surfactants – will move in response to surface waves. Owing to the difficulty of non-invasive measurement of the spatial distribution of a molecular monolayer, little is known about the dynamics that couple the surface waves and the evolving density field. Here, we report measurements of the spatiotemporal dynamics of the density field of an insoluble surfactant driven by gravity–capillary waves in a shallow cylindrical container. Standing Faraday waves and travelling waves generated by the meniscus are superimposed to create a non-trivial surfactant density field. We measure both the height field of the surface using moiré imaging, and the density field of the surfactant via the fluorescence of NBD-tagged phosphatidylcholine, a lipid. Through phase averaging stroboscopically acquired images of the density field, we determine that the surfactant accumulates on the leading edge...

吸附于流体表面的物质——例如原油、生物源浮膜或工业/医用表面活性剂——会随表面波发生运动。由于非侵入式测量分子单分子层空间分布存在难度，目前学界对耦合表面波与演化中密度场的动力学机制仍知之甚少。本文报道了浅圆柱容器中由重力-毛细波驱动的不溶性表面活性剂密度场的时空动力学测量结果。由弯液面产生的法拉第驻波（Faraday waves）与行波相互叠加，形成复杂的表面活性剂密度场。我们分别通过莫尔成像（moiré imaging）测量表面高度场，并借助经NBD标记的磷脂酰胆碱（一种脂质）的荧光信号获取表面活性剂的密度场。通过对频闪采集得到的密度场图像进行相位平均处理，我们发现表面活性剂会在波前前缘聚集……