Zhang Hongmin, Wu Yanchen, Wang Fei, Nestler Britta
Institute for Applied Materials-Microstructure Modelling and Simulation (IAM-MMS), Karlsruhe Institute of Technology (KIT), Straße am Forum 7, Karlsruhe 76131, Germany.
Institute of Nanotechnology, Karlsruhe Institute of Technology, Hermann-von-Helmholtz Pl. 1, 76344 Eggenstein-Leopoldshafen, Germany.
J Chem Phys. 2023 Oct 28;159(16). doi: 10.1063/5.0168394.
Cahn introduced the concept of wall energy to describe the interaction between two immiscible fluids and a solid wall [J. W. Cahn, J. Chem. Phys. 66, 3667-3672 (1977)]. This quintessential concept has been successfully applied to describe various wetting phenomena of a droplet in contact with a solid surface. The usually formulated wall free energy results in the so-called surface composition that is not equal to the bulk composition. This composition difference leads to a limited range of contact angles which can be achieved by the linear/high-order polynomial wall free energy. To address this issue and to improve the adaptability of the model, we symmetrically discuss the formulation of the wall free energy on the Young's contact angle via Allen-Cahn model. In our model, we modify the calculation of the fluid-solid interfacial tensions according to the Cahn's theory by considering the excess free energy contributed by the distorted composition profile induced by the surface effect. Additionally, we propose a semi-obstacle wall free energy which enforces the surface composition to be the bulk composition within the framework of bulk obstacle potential. By this way, the accuracy of the contact angle close to 0° and 180° is significantly improved in the phase-field simulations. We further reveal that the volume preservation term in the conservative Allen-Cahn model has a more significant impact on the wetting behavior on superhydrophobic surfaces than on hydrophilic surfaces, which is attributed to the curvature effect. Our findings provide alternative insights into wetting behavior on superhydrophilic and superhydrophobic surfaces.
卡恩引入了壁面能的概念来描述两种不混溶流体与固体壁面之间的相互作用[J. W. 卡恩，《化学物理杂志》66, 3667 - 3672 (1977)]。这个经典概念已成功应用于描述液滴与固体表面接触的各种润湿现象。通常表述的壁面自由能会导致所谓的表面组成与本体组成不相等。这种组成差异导致了通过线性/高阶多项式壁面自由能可实现的接触角范围有限。为了解决这个问题并提高模型的适应性，我们通过艾伦 - 卡恩模型对称地讨论了关于杨氏接触角的壁面自由能的表述。在我们的模型中，我们根据卡恩理论修改了流 - 固界面张力的计算，考虑了由表面效应引起的扭曲组成分布所贡献的过量自由能。此外，我们提出了一种半障碍物壁面自由能，它在体障碍物势的框架内强制表面组成成为本体组成。通过这种方式，在相场模拟中，接近0°和180°的接触角的精度得到了显著提高。我们进一步揭示，保守艾伦 - 卡恩模型中的体积守恒项对超疏水表面上的润湿行为的影响比对亲水表面的影响更大，这归因于曲率效应。我们的研究结果为超亲水和超疏水表面上的润湿行为提供了新的见解。
