Department of Chemical Engineering, Gebze Technical University, Gebze, 41400 Kocaeli, Türkiye.
Langmuir. 2023 May 9;39(18):6514-6528. doi: 10.1021/acs.langmuir.3c00471. Epub 2023 Apr 27.
Sessile drop evaporation and condensation on slippery liquid-infused porous surfaces (SLIPS) is crucial for many applications. However, its modeling is complex since the infused lubricant forms a wetting ridge around the drop close to the contact line, which partially blocks the free surface area and decreases the drop evaporation rate. Although a good model was available after 2015, the effects of initial lubricant heights () above the pattern, and the corresponding initial ridge heights (), lubricant viscosity, and solid pattern type were not well studied. This work fills this gap where water drop evaporations from SLIPS, which are obtained by infusing silicone oils (20 and 350 cSt) onto hydrophobized Si wafer micropatterns having both cylindrical and square prism pillars, are investigated under constant relative humidity and temperature conditions. With the increase of (), the corresponding () increased almost linearly on lower parts of the drops for all SLIPS samples, resulting in slower drop evaporation rates. A novel diffusion-limited evaporation equation from SLIPS is derived depending on the available free liquid-air interfacial area, , which represents the unblocked part of the total drop surface. The calculation of the diffusion constant, , of water vapor in air from (d/d) values obtained by drop evaporation was successful up to a threshold value of () = 8 μm within ±7%, and large deviations (13-27%) were obtained when () > 8 μm, possibly due to the formation of thin silicone oil cloaking layers on drop surfaces, which partially blocked evaporation. The increase of infused silicone oil viscosity caused only a slight increase (12-17%) in drop lifetimes. The effects of the geometry and size of the pillars on the drop evaporation rates were minimal. These findings may help optimize the lubricant oil layer thickness and viscosity used for SLIPS to achieve low operational costs in the future.
固着液滴在疏液性液体浸润多孔表面（SLIPS）上的蒸发和凝结对于许多应用至关重要。然而，由于注入的润滑剂在靠近接触线的液滴周围形成润湿脊，部分阻塞了自由表面积并降低了液滴蒸发速率，因此其建模较为复杂。尽管 2015 年后有了一个很好的模型，但初始润滑剂高度（）超过图案的高度以及相应的初始脊高度（）、润滑剂粘度和固体图案类型的影响尚未得到很好的研究。这项工作填补了这一空白，研究了通过将硅油（20 和 350 cSt）注入具有圆柱形和方形棱柱支柱的疏水性 Si 晶片微图案来获得的 SLIPS 上的水滴蒸发，在恒定相对湿度和温度条件下进行。随着（）的增加，所有 SLIPS 样品中液滴较低部分的相应（）几乎呈线性增加，导致液滴蒸发速率变慢。根据可用的自由液-气界面面积（），推导出了一个新的扩散限制蒸发方程，该方程代表了总液滴表面的未阻塞部分。通过液滴蒸发获得的（d/d）值计算水蒸气在空气中的扩散常数（）是成功的，直到（）= 8 μm 的阈值内偏差在±7%以内，当（）> 8 μm 时，会出现较大的偏差（13-27%），可能是由于液滴表面形成了薄的硅油包衣层，部分阻止了蒸发。注入硅油粘度的增加仅导致液滴寿命增加了 12-17%。支柱的几何形状和尺寸对液滴蒸发速率的影响最小。这些发现可能有助于优化 SLIPS 中使用的润滑剂油层厚度和粘度，以在未来实现低运营成本。
