Center of Smart Interfaces, Technical University Darmstadt , 64287 Darmstadt, Germany.
Mechanical Engineering Department, Dongguan University of Technology , 523808, Dongguan, China.
Langmuir. 2016 Aug 23;32(33):8322-8. doi: 10.1021/acs.langmuir.6b01357. Epub 2016 Aug 8.
Spreading of water drops resting in equilibrium on polypropylene surfaces was initiated by dispensing surfactant-laden droplets on their apex. Upon contact of the two drops two processes were kicked-off: surfactant from the droplets spread along the water/air interface of the sessile drops and a train of capillary waves propagated along the sessile drops. The contact line of the sessile drops remained initially pinned and started spreading only when surfactant reached it while the capillary waves did not have an apparent effect on initiating drop spreading. However, surfactant influenced the propagation velocity of the capillary waves. Though the spreading dynamics of such nonhomogeneously mixed surfactant/water drops on polypropylene surfaces was initially different from that of homogeneously mixed drops, the later spreading dynamics was similar and was dominated by viscosity and surface tension in both cases. These results can help in discriminating the path of action of surfactants in bulk and at the water/air interface, which is also relevant for understanding phenomena such as superspreading.
液滴在聚丙烯表面达到平衡时会扩散，在其顶点分配有表面活性剂的液滴会引发扩散。当两滴接触时，会引发两个过程：液滴中的表面活性剂沿着液滴的水/气界面扩散，并且沿液滴传播的一列毛细波。液滴的接触线最初被固定，只有当表面活性剂到达时才开始扩散，而毛细波对启动液滴扩散没有明显影响。然而，表面活性剂会影响毛细波的传播速度。尽管这种非均匀混合的表面活性剂/水液滴在聚丙烯表面上的扩散动力学最初与均匀混合液滴不同，但后来的扩散动力学相似，在两种情况下均由粘度和表面张力主导。这些结果可以帮助区分表面活性剂在体相和水/气界面上的作用途径，这对于理解超扩展等现象也很重要。
