Sharma Ashutosh, Verma Ruhi
Department of Chemical Engineering, Indian Institute of Technology, Kanpur, Kanpur 208 016, India.
Langmuir. 2004 Nov 9;20(23):10337-45. doi: 10.1021/la048669x.
Based on the complete 3D numerical solutions of the nonlinear thin film equation, we address the problems of surface instability, dynamics, morphological diversity and evolution in unstable thin films of the liquids that display complete macroscale wetting. The twin constraints of complete macroscale wettability and nanoscale instability produce a variety of microscopic morphological phases approximating sharp crystal surfaces with flat tops resembling a mesa or a micro "pancake" or a slice of Swiss cheese. While the maximum thickness of flat regions is found to be independent of the initial film thickness, the precise lateral morphology of microdomains formed depends on the film thickness. As the film thickness is increased, the initial pathway of evolution changes from the formation of small spherical droplets, to long mesas (parapets) and islands, to circular holes, all of which eventually resolve by ripening into a collection of round pancakes at equilibrium. However, beyond a certain transition thickness, a novel metastable honeycombed morphology, resembling a membrane or a slice of Swiss cheese, is uncovered, which is produced by an abrupt "freezing" of the evolution during hole growth. In contrast, the spinodal dewetting in thin films of partially wettable systems always engenders spherical droplets at equilibrium. The equilibrium dewetted area from simulations, as well as from simple mass balance, is shown to decline linearly with the initial film thickness.
基于非线性薄膜方程的完整三维数值解，我们研究了表现出完全宏观尺度润湿性的液体不稳定薄膜中的表面不稳定性、动力学、形态多样性和演化问题。完全宏观尺度润湿性和纳米尺度不稳定性这两个限制条件产生了多种微观形态相，这些相近似于具有平顶的尖锐晶体表面，类似台面、微型“薄饼”或瑞士奶酪片。虽然发现平坦区域的最大厚度与初始薄膜厚度无关，但形成的微区的精确横向形态取决于薄膜厚度。随着薄膜厚度增加，演化的初始路径从形成小的球形液滴，变为长台面（护堤）和岛状，再变为圆形孔洞，所有这些最终通过成熟演化为平衡状态下的一组圆形薄饼。然而，超过一定的转变厚度后，会发现一种新颖的亚稳蜂窝状形态，类似于薄膜或瑞士奶酪片，它是由孔洞生长过程中演化的突然“冻结”产生的。相比之下，部分可润湿性系统薄膜中的旋节线去湿在平衡时总是产生球形液滴。模拟以及简单质量平衡得到的平衡去湿面积显示随初始薄膜厚度呈线性下降。
