Wong William S Y, Kiseleva Mariia S, Naga Abhinav
Department of Applied Physics, School of Science, Aalto University, FI-02150 Espoo, Finland.
Department of Physics, Durham University, Durham DH1 3LE, U.K.
Langmuir. 2024 Jul 2;40(26):13562-13572. doi: 10.1021/acs.langmuir.4c01085. Epub 2024 Jun 14.
Wetting is typically defined by the relative liquid to solid surface tension/energy, which are composed of polar and nonpolar subcontributions. Current studies often assume that they remain invariant, that is, surfaces are wetting-inert. Complex wetting scenarios, such as adaptive or reactive wetting processes, may involve time-dependent variations in interfacial energies. To maximize differences in energetic states, we employ low-energy perfluoroalkyls integrated with high-energy silica-based polar moieties grown on low-energy polydimethylsiloxane. To this end, we tune the hydrophilic-like wettability on these perfluoroalkyl-silica-polydimethylsiloxane surfaces. Drop contact behaviors range from invariantly hydrophobic at ca. 110° to rapidly spreading at ca. 0° within 5 s. Unintuitively, these vapor-grown surfaces transit toward greater hydrophilicity with increasing perfluoroalkyl deposition. Notably, this occurs as sequential silica-and-perfluoroalkyl deposition also leaves behind embedded polar moieties. We highlight how surfaces having such chemical heterogeneity are inherently wetting-reactive. By creating an abrupt wetting transition composed of reactive and inert domains, we introduce spatial dependency. Drops contacting the transition spread before retracting, occurring over the time scale of a few seconds. This phenomenon contradicts current understanding, exhibiting a uniquely (1) decreasing advancing contact angle and (2) increasing receding contact angle. To explain the behavior, we model such time- and space- dependent reactive wetting using first order kinetics. In doing so, we explore how reactive and recovery mechanisms govern the characteristic time scales of spreading and retracting sessile drops.
润湿性通常由相对的液体与固体表面张力/能量来定义，它们由极性和非极性分量组成。当前的研究常常假定它们保持不变，也就是说，表面是润湿性惰性的。复杂的润湿情形，比如自适应或反应性润湿过程，可能涉及界面能随时间的变化。为了最大化能量状态的差异，我们采用与生长在低能聚二甲基硅氧烷上的高能硅基极性部分相结合的低能全氟烷基。为此，我们调节这些全氟烷基 - 二氧化硅 - 聚二甲基硅氧烷表面上类似亲水性的润湿性。液滴接触行为的范围从大约110°时不变的疏水性到大约0°时在5秒内迅速铺展。出乎意料的是，随着全氟烷基沉积量的增加，这些气相生长的表面会向更大的亲水性转变。值得注意的是，这种情况发生的同时，二氧化硅和全氟烷基的顺序沉积也会留下嵌入的极性部分。我们强调具有这种化学异质性的表面如何本质上是润湿性反应性的。通过创建由反应性和惰性区域组成的突然的润湿转变，我们引入了空间依赖性。接触转变区域的液滴在缩回之前会铺展，这发生在几秒的时间尺度上。这种现象与当前的理解相矛盾，表现出独特的（1）前进接触角减小和（2）后退接触角增大。为了解释这种行为，我们使用一级动力学对这种时间和空间依赖性的反应性润湿进行建模。在此过程中，我们探索反应性和恢复机制如何控制固定液滴铺展和缩回的特征时间尺度。
