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Pinning-Free Evaporation of Sessile Droplets of Water from Solid Surfaces
Langmuir ( IF 3.7 ) Pub Date : 2019-01-31 00:00:00 , DOI: 10.1021/acs.langmuir.8b03849 Steven Armstrong 1 , Glen McHale 1 , Rodrigo Ledesma-Aguilar 1 , Gary G. Wells 1
Langmuir ( IF 3.7 ) Pub Date : 2019-01-31 00:00:00 , DOI: 10.1021/acs.langmuir.8b03849 Steven Armstrong 1 , Glen McHale 1 , Rodrigo Ledesma-Aguilar 1 , Gary G. Wells 1
Affiliation
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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, omni-phobic covalently attached liquid-like coating. Our characterization of the surfaces shows high contact line mobility with an extremely low contact-angle hysteresis of ∼1° and reveals a step change in the value of the contact angle from 101° to 105° 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) °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, DE, of water vapor in air of DE = (2.44 ± 0.48) × 10–5 m2 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.
中文翻译：
固体表面上无水液滴的无钉蒸发
接触线钉扎是对固体表面上液体接触线运动的基本限制。当固着液滴蒸发时，接触线钉扎通常会导致粘滑滑动蒸发模式（在此模式下，接触线以不受控制的方式从表面钉住和从表面钉住），或者通过固定的接触线以恒定的接触面积模式发生。钉扎防止观察到准平衡的恒定接触角蒸发模式，而直接在光滑，无纹理的固体表面上固定的无水水滴从未观察到这种情况。在这里，我们报告了从处理过的光滑，光滑，全疏水共价附着的液体状涂层处理过的平板玻璃基板上蒸发的无固定液滴。我们对表面的表征显示出高的接触线迁移率，极低的接触角滞后约为1°，并且揭示了接触角值从101°到105°在相对湿度（RH）为30到200之间的阶跃变化。 40％，以使人想起在V型吸附等温线中观察到的转变。我们观察到在恒温条件下，小无柄小滴在室内蒸发，T =（25.0±0.1）°C，并且在RH = 10–70％的恒定RH下。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。此外，我们使用Picknett和Bexon理想的恒定接触角模式分析了扩散受限蒸发的蒸发序列。结果得出的水蒸气在空气中的扩散系数D E的估计值为D E =（2.44±0.48）×10 –5 m 2 s –1，精确到文献报道值的2％以内，因此可以验证扩散受限蒸发模型的恒定接触角模式。
更新日期：2019-01-31
中文翻译：
固体表面上无水液滴的无钉蒸发
接触线钉扎是对固体表面上液体接触线运动的基本限制。当固着液滴蒸发时，接触线钉扎通常会导致粘滑滑动蒸发模式（在此模式下，接触线以不受控制的方式从表面钉住和从表面钉住），或者通过固定的接触线以恒定的接触面积模式发生。钉扎防止观察到准平衡的恒定接触角蒸发模式，而直接在光滑，无纹理的固体表面上固定的无水水滴从未观察到这种情况。在这里，我们报告了从处理过的光滑，光滑，全疏水共价附着的液体状涂层处理过的平板玻璃基板上蒸发的无固定液滴。我们对表面的表征显示出高的接触线迁移率，极低的接触角滞后约为1°，并且揭示了接触角值从101°到105°在相对湿度（RH）为30到200之间的阶跃变化。 40％，以使人想起在V型吸附等温线中观察到的转变。我们观察到在恒温条件下，小无柄小滴在室内蒸发，T =（25.0±0.1）°C，并且在RH = 10–70％的恒定RH下。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。此外，我们使用Picknett和Bexon理想的恒定接触角模式分析了扩散受限蒸发的蒸发序列。结果得出的水蒸气在空气中的扩散系数D E的估计值为D E =（2.44±0.48）×10 –5 m 2 s –1，精确到文献报道值的2％以内，因此可以验证扩散受限蒸发模型的恒定接触角模式。
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