Deng Q, Anilkumar A V, Wang T G
Department of Mechanical Engineering, Vanderbilt University, Nashville, TN 37235, USA.
J Colloid Interface Sci. 2009 May 15;333(2):523-32. doi: 10.1016/j.jcis.2009.02.027. Epub 2009 Feb 20.
Polymer capsules are formed following the impact of viscous poly-anion drops onto a deep pool of water-like poly-cation solution. During impact, an air bubble is often trapped on the drop/capsule surface, affecting the membrane quality locally. This entrapment has been experimentally examined for a typical anion-cation pair through detailed imaging of the impact crater. Experiments show that the bubble entrapment is caused by the collapse of the impact crater above the top surface of the submerged-and-reacting drop. Locally, the bubble pinch-off can be viewed as the continuous thinning of a gas filament driven by the rebounding bulk flow. In the low impact Weber number (We) regime, the data suggests that both surface tension and inertia govern the entrapment process, whereas, for higher Weber numbers the process is inertia-dominated. The transition condition is found to be coincident with the observation of the critical cone angle for the impact crater, seen in inviscid non-reacting drop impact.
聚合物胶囊是在粘性聚阴离子液滴撞击深水池状聚阳离子溶液时形成的。在撞击过程中，气泡常常被困在液滴/胶囊表面，局部影响膜的质量。通过对撞击坑的详细成像，已对典型的阴离子-阳离子对的这种截留现象进行了实验研究。实验表明，气泡截留是由浸没并发生反应的液滴顶表面上方撞击坑的坍塌引起的。局部而言，气泡的夹断可视为由反弹的整体流驱动的气体细丝的持续变细。在低撞击韦伯数（We） regime下，数据表明表面张力和惯性都控制着截留过程，而对于较高的韦伯数，该过程以惯性为主导。发现转变条件与在无粘性非反应液滴撞击中观察到的撞击坑临界锥角一致。
