Contact Angles of Liquid Drops on Super Hydrophobic Surfaces: Understanding the Role of Flattening of Drops by Gravity
Contact Angles of Liquid Drops on Super Hydrophobic Surfaces: Understanding the Role of Flattening of Drops by Gravity
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DOI：
10.1021/la102566c
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发表时间：
2010-11-16
期刊：
影响因子：
3.9
通讯作者：
Moon, Sung In
中科院分区：
文献类型：
--
作者：
Extrand, C. W.;Moon, Sung In
通过传统方法测量超疏水表面或接触角可能会产生不明确的结果。构建切线的实验困难、重力扭曲或有关扩散程度的错误假设可能会导致接触角的低估。使用三个模型来估计完全不润湿的超疏水表面上的液滴形状和感知接触角。其中一个模型采用了 Bashforth 和 Adams 的经典数值解。此外，作为这项工作的一部分，还得出了两个近似模型。所有这三个都显示出微升大小的液滴的显着变形以及感知接触角的类似趋势。传统上，在固着接触角测量中使用几微升的液滴。即使润湿相互作用很小，这种尺寸的液滴预计也会在超疏水表面上发生显着的扁平化。如果液体具有较小的表面张力或较大的密度，则变形更加明显。适用于完全不润湿的表面。接触角的低估可能是几十度。我们的建模工作表明，在超疏水表面上进行精确的接触角测量需要非常小的固着滴。大约数百皮升。
Measurement or contact angles on super hydrophobic surfaces by conventional methods can produce ambiguous results. Experimental difficulties in constructing tangent lines, gravitational distortion or erroneous assumptions regarding the extent of spreading can lead to underestimation of contact angles. Three models were used to estimate drop shape and perceived contact angles on completely nonwetting super hydrophobic surfaces. One of the models employed the classic numerical solutions from Bashforth and Adams. Additionally, two approximate models were derived as part of this work. All three showed significant distortion of microliter-sized drops and similar trends in perceived contact angles. Liquid drops of several microliters are traditionally used in sessile contact angle measurements. Drops of this size are expected to and indeed undergo significant flattening on super hydrophobic surfaces, even if the wetting interactions are minimal. The distortion is more pronounced if the liquid has a lesser surface tension or greater density. For surfaces that are completely nonwetting. underestimation of contact angles can be tens of degrees. Our modeling efforts suggest that accurate contact angle measurements on super hydrophobic surfaces would require very small sessile drops. on the order of hundreds of picoliters.