Extreme Materials Research Center, Korea Institute of Science and Technology, Seoul 02792, Republic of Korea.
Department of Materials Science and Engineering, Korea University, Seoul 02841, Republic of Korea.
Proc Natl Acad Sci U S A. 2022 Dec 13;119(50):e2209586119. doi: 10.1073/pnas.2209586119. Epub 2022 Dec 5.
Liquid mobility is ubiquitous in nature, with droplets emerging at all size scales, and artificial surfaces have been designed to mimic such mobility over the past few decades. Meanwhile, millimeter-sized droplets are frequently used for wettability characterization, even with facial mask applications, although these applications have a droplet-size target range that spans from millimeters to aerosols measuring less than a few micrometers. Unlike large droplets, microdroplets can interact sensitively with the fibers they contact with and are prone to evaporation. However, wetting behaviors at the single-microfiber level remain poorly understood. Herein, we characterized the wettability of fibrous layers, which revealed that a multiscale landscape of droplets ranged from the millimeter to the micrometer scale. The contact angle (CA) values of small droplets on pristine fibrous media showed sudden decrements, especially on a single microfiber, owing to the lack of air cushions for the tiny droplets. Moreover, droplets easily adhered to the pristine layer during droplet impact tests and then yielding widespread areas of contamination on the microfibers. To resolve this, we carved nanowalls on the pristine fibers by plasma etching, which effectively suppressed such wetting phenomena. Significantly, the resulting topographies of the microfibers managed the dynamic wettability of droplets at the multiscale, which reduced the probability of contamination with impact droplets and suppressed the wetting transition upon evaporation. These findings for the dynamic wettability of fibrous media will be useful in the fight against infectious droplets.
液体的流动性在自然界中无处不在，各种大小的液滴都会出现，在过去几十年中，人们设计了人工表面来模拟这种流动性。与此同时，毫米大小的液滴经常被用于润湿性表征，即使是在口罩应用中，尽管这些应用的液滴尺寸目标范围从毫米跨越到小于几微米的气溶胶。与大液滴不同，微液滴与它们接触的纤维会发生敏感的相互作用，并且容易蒸发。然而，单纤维水平上的润湿行为仍未得到很好的理解。在这里，我们对纤维层的润湿性进行了表征，结果表明，液滴具有从毫米到微米的多尺度景观。在原始纤维介质上的小液滴的接触角（CA）值突然下降，尤其是在单个微纤维上，这是由于微小液滴缺乏气垫。此外，在液滴冲击测试中，液滴容易附着在原始层上，然后在微纤维上产生广泛的污染区域。为了解决这个问题，我们通过等离子体蚀刻在原始纤维上刻蚀纳米壁，有效地抑制了这种润湿现象。值得注意的是，微纤维的这种形貌有效地管理了液滴在多尺度下的动态润湿性，降低了冲击液滴污染的概率，并抑制了蒸发过程中的润湿转变。这些关于纤维介质动态润湿性的发现将有助于对抗传染性液滴。
