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Time-Dependent Wetting Behavior of PDMS Surfaces with Bioinspired, Hierarchical Structures

机译:具有生物启发性,分层结构的PDMS表面的时间依赖性润湿行为

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Wetting of rough surfaces involves time-dependent effects, such as surface deformations, nonuniform filling of surface pores within or outside the contact area, and surface chemistries, but the detailed impact of these phenomena on wetting is not entirely clear. Understanding these effects is crucial for designing coatings for a wide range of applications, such as membrane-based oil water separation and desalination, waterproof linings/windows for automobiles, aircrafts, and naval vessels, and antibiofouling. Herein, we report on time-dependent contact angles of water droplets on a rough polydimethylsiloxane (PDMS) surface that cannot be completely described by the conventional Cassie-Baxter or Wenzel models or the recently proposed Cassie-impregnated model. Shells of sand dollars (Dendraster excentricus) were used as lithography-free, robust templates to produce rough PDMS surfaces with hierarchical, periodic features ranging from 1 x 10(-7) to 1 x 10(-4) m. Under saturated vapor conditions, we found that in the short term (<1 min), the contact angle of a sessile water droplet on the templated PDMS, theta(SDT) = 140 +/- 3 degrees, was accurately described by the Cassie-Baxter model (predicted theta(SDT) = 137 degrees); however, after 90 min, theta(SDT) fell to 110 degrees. Fluorescent confocal microscopy confirmed that the initial reduction in theta(SDT) to 110 degrees (the Wenzel limit) was primarily a Cassie Baxter to Wenzel transition during which pores within the contact area filled gradually, and more rapidly for ethanol water mixtures. After 90 min, the contact line of the water droplet became pinned, perhaps caused by viscoelastic deformation of the PDMS around the contact line, and a significant volume of water began to flow from the droplet to pores outside the contact region, causing theta(SDT) to decrease to 65 degrees over 48 h on the rough surface. The system we present here to explore the concept of contact angle time dependence (dynamics) and modeling of natural surfaces provides insights into the design and development of long- and short-lived coatings.
机译:粗糙表面的润湿涉及时间相关的影响,例如表面变形,接触区域内外的表面孔隙填充不均匀以及表面化学性质,但是这些现象对润湿的详细影响尚不完全清楚。了解这些影响对于设计用于广泛应用的涂料至关重要,例如基于膜的油水分离和脱盐,汽车,飞机和海军舰船的防水衬里/窗户以及防污垢。在这里,我们报道了粗糙的聚二甲基硅氧烷(PDMS)表面上的水滴随时间变化的接触角,而传统的Cassie-Baxter或Wenzel模型或最近提出的Cassie浸渍模型无法完全描述水滴的接触角。沙钱壳(Dendraster excentricus)被用作无光刻,坚固的模板,以产生粗糙的PDMS表面,该表面具有分层的周期性特征,范围从1 x 10(-7)到1 x 10(-4)m。在饱和蒸汽条件下,我们发现在短时间内(<1分钟),Cassie精确地描述了无水水滴在模板化PDMS上的接触角theta(SDT)= 140 +/- 3度。百特模型(预测theta(SDT)= 137度);但是,在90分钟后,theta(SDT)降至110度。荧光共聚焦显微镜证实,theta(SDT)最初降低至110度(Wenzel极限)主要是由Cassie Baxter到Wenzel的转变,在此期间接触区域内的孔逐渐填充,而乙醇水混合物则更快。 90分钟后,水滴的接触线被钉住,这可能是由于PDMS围绕接触线的粘弹性变形所致,并且大量的水开始从水滴流向接触区域外部的孔,从而导致theta(SDT) )在粗糙表面上经过48小时降低到65度。我们在此展示的用于探索接触角时间相关性(动力学)和自然表面建模概念的系统为洞察长寿命和短寿命涂层的设计和开发提供了见识。

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