Goto Ren, Oshima Yuki, Yamaguchi Masaki
Graduate School of Medicine, Science and Technology, Shinshu University, 3-15-1 Tokida, Ueda, Nagano, 386-8567, Japan.
Sci Rep. 2024 Dec 4;14(1):30228. doi: 10.1038/s41598-024-81778-0.
Biomimetic periodic structures have garnered attention due to their excellent water repellency. The normal-taper angle, which is aspects of the cross-sectional structure, is important factor in achieving water repellency and pressure resistance; however, the underlying physical phenomenon has not been fully explained. Moreover, once a surface becomes hydrophobic, it is difficult to measure the apparent contact angle. The purpose of this paper is to clarify the taper angle that provides high water repellency under pressure impact conditions by formulating the relationship between the taper angle and the height of a droplet bouncing, instead of traditional contact angles, using experimental results. We fabricated multiple samples with different taper angles and groove width/tooth width ratios, through micro-processing using a femtosecond-pulsed laser and a control algorithm, and investigated their effects on water repellency. By using height of a droplet bouncing as an evaluation parameter, we were able to effectively differentiate between taper angles in terms of water repellency. Additionally, we suggested that in the bouncing phenomenon, where droplets are given velocity by falling, the sidewall of the periodic structure and the taper angle affect liquid repellency. To explain this phenomenon, we proposed a pressured-taper angle model where a droplet is pressed against the taper angle. Based on both experimental findings and the pressured-taper angle model, a relationship between the equilibrium contact angle, the taper angle, and the lifting force angle was revealed. Moreover, using this pressured-taper angle model, the taper angle of the periodic structure to achieve maximum liquid repellency was estimated from the equilibrium contact angle of the base material.
仿生周期性结构因其出色的疏水性而备受关注。作为横截面结构的一个方面，正锥角是实现疏水性和耐压性的重要因素；然而，其潜在的物理现象尚未得到充分解释。此外，一旦表面变得疏水，就很难测量表观接触角。本文的目的是通过利用实验结果，建立锥角与液滴弹跳高度之间的关系，而不是传统的接触角，来阐明在压力冲击条件下提供高疏水性的锥角。我们通过飞秒脉冲激光微加工和控制算法制造了多个具有不同锥角和槽宽/齿宽比的样品，并研究了它们对疏水性的影响。通过将液滴弹跳高度作为评估参数，我们能够有效地根据疏水性区分锥角。此外，我们认为在液滴因下落而获得速度的弹跳现象中，周期性结构的侧壁和锥角会影响液体排斥性。为了解释这一现象，我们提出了一个压力锥角模型，其中液滴被压在锥角上。基于实验结果和压力锥角模型，揭示了平衡接触角、锥角和升力角之间的关系。此外，利用这个压力锥角模型，根据基材的平衡接触角估计了实现最大液体排斥性的周期性结构的锥角。
