Pinning-Free Evaporation of Sessile Droplets of Water from Solid Surfaces
Pinning-Free Evaporation of Sessile Droplets of Water from Solid Surfaces
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DOI：
10.1021/acs.langmuir.8b03849
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发表时间：
2019-02-26
期刊：
影响因子：
3.9
通讯作者：
Wells, Gary G.
中科院分区：
文献类型：
--
作者：
Armstrong, Steven;McHale, Glen;Wells, Gary G.
接触线固定是液体在固体表面上接触线运动的一个基本限制。当无基液滴蒸发时，接触线固定通常会导致粘滑蒸发模式，其中接触线以不受控制的方式从表面销钉和下沉，或者固定接触线的恒定接触区域模式。钉住防止观察到准平衡常数接触角模式的蒸发，这是从未观察到的固定水滴直接停留在光滑，无纹理，固体表面。在这里，我们报告了在光滑、光滑、全疏共价附着的液体状涂层处理的平板玻璃基板上的无根液滴的蒸发。我们对表面的表征表明，接触线迁移率高，接触角迟滞极低，约为1度，并且在相对湿度（RH）为30和40%之间，接触角的值从101度到105度呈阶梯变化，这让人想起在V型吸附等温线中观察到的转变。我们在恒温(T =(25.0 +/- 0.1)℃和恒定RH （RH = 10-70%）范围内观察小液滴的蒸发。在所有情况下，在大部分蒸发时间内都观察到恒定的接触角蒸发模式。在此基础上，利用Picknett和Bexon理想恒接触角模型分析了扩散限制蒸发的蒸发序列。由此得到的空气中水蒸气的扩散系数D-E = (2.44 +/- 0.48) X 10(-5) m(2) s（-1）的估计精度在文献报道值的2%以内，从而验证了扩散限制蒸发模型的恒定接触角模式。
Contact-line pinning is a fundamental limitation to the motion of contact lines of liquids on solid surfaces. When a sessile droplet evaporates, contact-line pinning typically results in either a stick-slip evaporation mode, where the contact line pins and depins from the surface in an uncontrolled manner, or a constant contact-area mode with a pinned contact line. Pinning prevents the observation of the quasi-equilibrium constant contact-angle mode of evaporation, which has never been observed for sessile droplets of water directly resting on a smooth, nontextured, solid surface. Here, we report the evaporation of a sessile droplet from a flat glass substrate treated with a smooth, slippery, omniphobic covalently attached liquid-like coating. Our characterization of the surfaces shows high contact line mobility with an extremely low contact angle hysteresis of similar to 1 degrees and reveals a step change in the value of the contact angle from 101 degrees to 105 degrees between a relative humidity (RH) of 30 and 40%, in a manner reminiscent of the transition observed in a type V adsorption isotherm. We observe the evaporation of small sessile droplets in a chamber held at a constant temperature, T = (25.0 +/- 0.1) degrees C and at constant RH across the range RH = 10-70%. In all cases, a constant contact-angle mode of evaporation is observed for most of the evaporation time. Furthermore, we analyze the evaporation sequences using the Picknett and Bexon ideal constant contact-angle mode for diffusion-limited evaporation. The resulting estimate for the diffusion coefficient, D-E, of water vapor in air of D-E = (2.44 +/- 0.48) X 10(-5) m(2) s(-1) is accurate to within 2% of the value reported in the literature, thus validating the constant contact-angle mode of the diffusion-limited evaporation model.