近日，芬兰阿尔托大学的Robin H. A. Ras&Matilda Backholm及其研究团队取得一项新进展。经过不懈努力，他们成功接近在防水表面上消除液滴摩擦
据悉，超疏水表面通常被视为无摩擦材料，水在其上具有高度的流动性。深入探究这种防水系统的摩擦特性，对于减少实际应用中的运动阻力和能量损耗具有重要意义。尤其在液滴缓慢移动的情况下，接触线摩擦往往成为影响超疏水表面性能的关键因素。
该研究团队证明这个一般规则只适用于非常低的速度。研究人员利用微管力传感器在振荡模式下进行了精细测量，发现水滴的摩擦在接近甚至达到零接触线摩擦时依然存在。研究人员证实这种摩擦耗散主要来源于被液体下方捕获的气膜（板）所产生的粘性剪切力。由于这种力与速度密切相关，因此，在看似非常光滑的表面上进行的准静态测试中，它可能成为一个不可忽视的阻力源。此外，研究还发现板厚是调控这种特殊摩擦的关键参数，这一发现对于设计下一代超滑防水涂层具有重要意义。
附：英文原文
Title: Toward vanishing droplet friction on repellent surfaces
Author: Backholm, Matilda, Krki, Tytti, Nurmi, Heikki A., Vuckovac, Maja, Turkki, Valtteri, Lepikko, Sakari, Jokinen, Ville, Quéré, David, Timonen, Jaakko V. I., Ras, Robin H. A.
Issue&Volume: 2024-4-15
Abstract: Superhydrophobic surfaces are often seen as frictionless materials, on which water is highly mobile. Understanding the nature of friction for such water-repellent systems is central to further minimize resistance to motion and energy loss in applications. For slowly moving drops, contact-line friction has been generally considered dominant on slippery superhydrophobic surfaces. Here, we show that this general rule applies only at very low speed. Using a micropipette force sensor in an oscillating mode, we measure the friction of water drops approaching or even equaling zero contact-line friction. We evidence that dissipation then mainly stems from the viscous shearing of the air film (plastron) trapped under the liquid. Because this force is velocity dependent, it can become a serious drag on surfaces that look highly slippery from quasi-static tests. The plastron thickness is found to be the key parameter that enables the control of this special friction, which is useful information for designing the next generation of ultraslippery water-repellent coatings.
DOI: 10.1073/pnas.2315214121
Source: https://www.pnas.org/doi/abs/10.1073/pnas.2315214121