Liang Yu-En, Tsao Heng-Kwong, Sheng Yu-Jane
Department of Chemical Engineering, National Taiwan University , Taipei, Taiwan 106.
Langmuir. 2015 Feb 10;31(5):1704-10. doi: 10.1021/la504552d. Epub 2015 Jan 28.
Controlling the droplet equilibrium location and shape on a conical fiber is essential to industrial applications such as dip-pen nanolithography. In this work, the equilibrium conformations of a drop on a vertical, conical fiber has been investigated by the finite element method, Surface Evolver simulations. Similar to the morphology of a drop on a cylinder, two different types (barrel shape and clam-shell shape) can be obtained. In the absence of gravity, the droplet moves upward (lower curvature) and the total surface energy decays as the drop ascends. Whatever the initial conformation of the drop on a conical fiber, the rising drop exhibits the clam-shell shape eventually and there is no equilibrium location. However, in the presence of gravity, the drop can stop at the equilibrium location stably. For a given contact angle, the clam-shell shape is generally favored for smaller drops but the barrel shape is dominant for larger drops. In a certain range of drop volume, the coexistence of both barrel and clam-shell shapes is observed. For large enough drops, the falling-off state is seen.
控制液滴在锥形纤维上的平衡位置和形状对于诸如蘸笔纳米光刻等工业应用至关重要。在这项工作中，通过有限元方法和表面演化器模拟研究了垂直锥形纤维上液滴的平衡构象。与圆柱上液滴的形态类似，可以得到两种不同类型（桶形和蛤壳形）。在没有重力的情况下，液滴向上移动（曲率变小），并且随着液滴上升，总表面能衰减。无论锥形纤维上液滴的初始构象如何，上升的液滴最终都会呈现蛤壳形，并且不存在平衡位置。然而，在有重力的情况下，液滴可以稳定地停留在平衡位置。对于给定的接触角，较小的液滴通常更倾向于蛤壳形，而较大的液滴则以桶形为主。在一定的液滴体积范围内，可以观察到桶形和蛤壳形同时存在。对于足够大的液滴，可以看到脱落状态。
