Shardt Nadia, Bigdeli Masoud Bozorg, Elliott Janet A W, Tsai Peichun Amy
Department of Chemical and Materials Engineering , University of Alberta , Edmonton , Alberta T6G 1H9 , Canada.
Department of Mechanical Engineering , University of Alberta , Edmonton , Alberta T6G 1H9 , Canada.
J Phys Chem Lett. 2019 Dec 5;10(23):7510-7515. doi: 10.1021/acs.jpclett.9b02802. Epub 2019 Nov 25.
Surfactants, as amphiphilic molecules, adsorb easily at interfaces and can detrimentally destroy the useful, gas-trapping wetting state (Cassie-Baxter, CB) of a drop on superhydrophobic surfaces. Here, we provide a quantitative understanding of how surfactants alter the wetting state and contact angle of aqueous drops on hydrophobic microstructures of different roughness () and solid fraction (ϕ). Experimentally, at low surfactant concentrations (), some drops attain a homogeneous wetting state (Wenzel, W), while others attain the CB state whose large contact angles can be predicted by a thermodynamic model. In contrast, all of our high- drops attain the Wenzel state. To explain this observed transition, we consider the free energy and find that, theoretically, for our surfaces the W state is always preferred, while the CB state is metastable at low , consistent with experimental results. Furthermore, we provide a beneficial blueprint for stable CB states for applications exploiting superhydrophobicity.
表面活性剂作为两亲分子，容易吸附在界面上，并可能有害地破坏超疏水表面上液滴的有用的气体捕获润湿状态（卡西-巴克斯特，CB）。在这里，我们定量地了解了表面活性剂如何改变不同粗糙度（）和固体分数（ϕ）的疏水微结构上水滴的润湿状态和接触角。实验表明，在低表面活性剂浓度（）下，一些液滴达到均匀润湿状态（文泽尔，W），而另一些液滴达到CB状态，其大接触角可以通过热力学模型预测。相比之下，我们所有的高浓度液滴都达到了文泽尔状态。为了解释这种观察到的转变，我们考虑了自由能，发现从理论上讲，对于我们的表面，W状态总是更可取的，而CB状态在低浓度下是亚稳态的，这与实验结果一致。此外，我们为利用超疏水性的应用提供了稳定CB状态的有益蓝图。
