A combined ab initio modeling and experimental study of water adsorption on a dry hydrophobic dielectric surface is presented. This is an important phenomenon for controlled droplet deposition in various technological applications. The ab initio density functional theory calculations are performed to reveal the dominant water adsorption sites, energetics, and the electron density profile on Teflon and parafilm surfaces. Several surface states such as stretched, nondefective, and defective are considered for water adsorption studies. It is revealed that stretching of nondefective surface leads to weaker water adsorption compared to an unstretched surface. Accordingly, such stretching makes the surface more hydrophobic as revealed by the electron density profile. The introduction of random defects into Teflon and parafilm surfaces results in an increase in water adsorption energy leading, in some cases, to practically hydrophilic interactions. These findings are in good agreement with the present measurements of static contact angle on prestretched Teflon and parafilm samples, where stretching not only elongates interatomic bonds but also changes the surface roughness. Thus, the present combined modeling and experimental study allows for a mechanistic interpretation of the reasons behind the change of wettability of dry hydrophobic surfaces.

中文翻译：

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水与介电表面的相互作用：从头算和实验研究的结合

提出了从头开始的组合模型和干燥的疏水介电表面上水吸附的实验研究。这是在各种技术应用中受控液滴沉积的重要现象。该从头进行密度泛函理论计算，以揭示聚四氟乙烯和旁膜表面上主要的水吸附位，高能学和电子密度分布。考虑了几种表面状态，例如拉伸，无缺陷和有缺陷，以进行水吸附研究。据揭示，与未拉伸的表面相比，无缺陷的表面的拉伸导致较弱的水吸附。因此，如电子密度分布所揭示的，这种拉伸使表面更疏水。在特氟隆和封口膜表面引入随机缺陷会导致水吸附能增加，在某些情况下会导致实际的亲水性相互作用。这些发现与目前对预拉伸的特氟龙和封口膜样品的静态接触角的测量结果非常吻合，拉伸不仅延长了原子间键，而且改变了表面粗糙度。因此，本发明的组合建模和实验研究允许对干燥的疏水性表面的润湿性变化背后的原因进行机械解释。