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Water droplet friction and rolling dynamics on superhydrophobic surfaces
Communications Materials Pub Date : 2020-09-15 , DOI: 10.1038/s43246-020-00065-3
Matilda Backholm , Daniel Molpeceres , Maja Vuckovac , Heikki Nurmi , Matti J. Hokkanen , Ville Jokinen , Jaakko V. I. Timonen , Robin H. A. Ras

Superhydrophobicity is a remarkable surface property found in nature and mimicked in many engineering applications, including anti-wetting, anti-fogging, and anti-fouling coatings. As synthetic superhydrophobic coatings approach the extreme non-wetting limit, quantification of their slipperiness becomes increasingly challenging: although contact angle goniometry remains widely used as the gold standard method, it has proven insufficient. Here, micropipette force sensors are used to directly measure the friction force of water droplets moving on super-slippery superhydrophobic surfaces that cannot be quantified with contact angle goniometry. Superhydrophobic etched silicon surfaces with tunable slipperiness are investigated as model samples. Micropipette force sensors render up to three orders of magnitude better force sensitivity than using the indirect contact angle goniometry approach. We directly measure a friction force as low as 7 ± 4 nN for a millimetric water droplet moving on the most slippery surface. Finally, we combine micropipette force sensors with particle image velocimetry and reveal purely rolling water droplets on superhydrophobic surfaces.



中文翻译:

超疏水表面上的水滴摩擦和滚动动力学

超疏水性是自然界中发现的一种卓越的表面性能,在许多工程应用中都被模仿,包括防湿,防雾和防污涂料。随着合成超疏水性涂料接近极限非润湿性极限,其光滑度的量化变得越来越具有挑战性:尽管接触角测角法仍被广泛用作金标准方法,但事实证明,这种方法不足。在这里,微吸管力传感器用于直接测量在超滑超疏水表面上移动的水滴的摩擦力,而这些摩擦力无法通过接触角测角法进行量化。具有可调节滑度的超疏水蚀刻硅表面被用作模型样品。与使用间接接触角测角方法相比,微量移液器力传感器可提供高达三个数量级更好的力灵敏度。对于在最光滑的表面上移动的毫米水滴,我们直接测量低至7±4 nN的摩擦力。最后,我们将微量移液器力传感器与颗粒图像测速仪结合起来,揭示了超疏水表面上纯滚动的水滴。

更新日期:2020-09-15
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