Mourougou-Candoni N, Prunet-Foch B, Legay F, Vignes-Adler M, Wong K
Laboratoire des Phenomenes de Transport dans les Melanges du CNRS, 4 ter route des Gardes, F-Meudon, 92190, France
J Colloid Interface Sci. 1997 Aug 1;192(1):129-41. doi: 10.1006/jcis.1997.4989.
We have investigated the impact of single droplets of various surfactant solutions on a low-surface-energy solid substrate using a high-frequency visualization technique (one picture every 100 μs). Whatever the surfactant, the drop spreads and retracts in about 1 s under the action of inertia and capillarity, respectively. During retraction, the capillary waves can be amplified and, in some cases, even yield droplet bouncing. Then, the droplet may slowly spread again due to gravity and the unbalanced capillary forces at the contact line between the droplet and the substrate. During the fast spreading process (2-3 ms), the droplet surface increases by almost one order of magnitude since its shape changes from a sphere to a flat pancake; this causes a strong deviation from thermodynamic equilibrium. The relevant surface property is therefore the dynamic surface tension which we have evaluated using a maximum bubble pressure apparatus. We have shown that droplet retraction is drastically influenced by the adsorption kinetics of the surfactant which limits the return to equilibrium surface tension.
我们使用高频可视化技术（每100微秒拍摄一张照片）研究了各种表面活性剂溶液的单滴对低表面能固体基材的影响。无论使用何种表面活性剂，液滴在惯性和毛细作用下分别在约1秒内铺展和回缩。在回缩过程中，毛细波可能会被放大，在某些情况下甚至会导致液滴反弹。然后，由于重力以及液滴与基材接触线处不平衡的毛细力，液滴可能会再次缓慢铺展。在快速铺展过程（2 - 3毫秒）中，液滴表面由于其形状从球体变为扁平薄饼而增加了近一个数量级；这导致与热力学平衡有很大偏差。因此，相关的表面性质是动态表面张力，我们使用最大气泡压力装置对其进行了评估。我们已经表明，液滴回缩受到表面活性剂吸附动力学的极大影响，而表面活性剂吸附动力学限制了向平衡表面张力的恢复。
