Katasho Yumi, Liang Yunfeng, Murata Sumihiko, Fukunaka Yasuhiro, Matsuoka Toshifumi, Takahashi Satoru
Environment and Resource System Engineering, Kyoto University, Kyoto 615-8540, Japan.
Japan Oil, Gas and Metals National Corporation (JOGMEC), Chiba 261-0025, Japan.
Sci Rep. 2015 Sep 4;5:13790. doi: 10.1038/srep13790.
It is well known that the close-packed CF3-terminated solid surface is among the most hydrophobic surfaces in nature. Molecular dynamic simulations show that this hydrophobicity can be further enhanced by the atomic-scale roughness. Consequently, the hydrophobic gap width is enlarged to about 0.6 nm for roughened CF3-terminated solid surfaces. In contrast, the hydrophobic gap width does not increase too much for a rough CH3-terminated solid surface. We show that the CF3-terminated surface exists in a microscopic Cassie-Baxter state, whereas the CH3-terminated surface exists as a microscopic Wenzel state. This finding elucidates the underlying mechanism for the different widths of the observed hydrophobic gap. The cage structure of the water molecules (with integrated hydrogen bonds) around CH3 terminal assemblies on the solid surface provides an explanation for the mechanism by which the CH3-terminated surface is less hydrophobic than the CF3-terminated surface.
众所周知，紧密堆积的CF₃端基固体表面是自然界中疏水性最强的表面之一。分子动力学模拟表明，这种疏水性可通过原子尺度的粗糙度进一步增强。因此，对于粗糙的CF₃端基固体表面，疏水间隙宽度增大到约0.6纳米。相比之下，对于粗糙的CH₃端基固体表面，疏水间隙宽度增加不多。我们表明，CF₃端基表面以微观的Cassie-Baxter状态存在，而CH₃端基表面以微观的Wenzel状态存在。这一发现阐明了观察到的疏水间隙宽度不同的潜在机制。固体表面上CH₃末端组装体周围水分子的笼状结构（带有整合的氢键）为CH₃端基表面疏水性低于CF₃端基表面的机制提供了解释。
