Surface interactions between chemically mixed surfaces, as well as those among dissolved biomolecules, comprise distinct contributions from polar and hydrophobic moieties. These contributions are often context dependent. Approximate compliance to the Cassie additivity equation for the wetting free energies on mixed surfaces in water is, however, indicative of similarly additive forces between individual surface elements, suggesting a quadratic interpolation model for total force from the forces between pure surfaces. We use molecular dynamics/umbrella sampling simulations of parallel and nonparallel mixed surfaces with demonstrable Cassie-like behavior to verify how well the total surface force between the heterogeneous, molecularly rough surfaces can be approximated as a combination of forces among the homogeneous ones. When accounting for dissimilar distances of approach between functional groups of different types, our results for graphene surfaces with mixed methyl and nitrile coating show such a superposition to provide a reasonable first order approximation of interactions between the platelets. Deviations from additivity are more prominent in parallel-plate configurations, at high content of hydrophobic groups, and small separations. The inclusion of water polarizability does not visibly alter the observed behavior regardless of platelet orientations. The outcome of this study determines the necessary molecular conditions for observing force additivity that emphasize the context dependence of hydrophobic interaction in the presence of polar groups. This notion provides guidelines for the syntheses of new, chemically heterogeneous materials with tailored function-oriented properties in aqueous media.

中文翻译：

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不同方向的化学异质基底上表面力加和的程度

化学混合表面之间以及溶解的生物分子之间的表面相互作用包括极性和疏水部分的独特贡献。这些贡献通常取决于上下文。然而，对于水在混合表面上润湿自由能的Cassie可加性方程式的近似顺应性表明，各个表面元素之间的相加力相似，这暗示了纯表面之间的力的总力的二次插值模型。我们使用分子动力学/伞状采样模拟具有可证明的Cassie行为的平行和非平行混合表面，以验证异质，分子粗糙表面之间的总表面力可以近似地反映为均质表面之间的力组合。当考虑到不同类型的官能团之间接近的距离不同时，我们对具有混合的甲基和腈涂层的石墨烯表面的结果显示出这种叠加，从而为血小板之间的相互作用提供了合理的一阶近似值。在平行板结构中，疏水基团含量高且分离距离小时，与可加性的差异更为突出。不管血小板的取向如何，水极化率的存在都不会明显改变观察到的行为。这项研究的结果确定了观察力加性的必要分子条件，该条件强调了极性基团存在时疏水相互作用的环境依赖性。这个概念为合成新的，