Université Paris-Saclay, Univ Evry, CNRS, LAMBE UMR8587, 91025 Evry-Courcouronnes, France.
Department of Physical Chemistry II, Ruhr University Bochum, D-44801 Bochum, Germany.
J Phys Chem Lett. 2021 Apr 22;12(15):3827-3836. doi: 10.1021/acs.jpclett.1c00257. Epub 2021 Apr 14.
Hydrophobicity/hydrophilicity of aqueous interfaces at the molecular level results from a subtle balance in the water-water and water-surface interactions. This is characterized here via density functional theory-molecular dynamics (DFT-MD) coupled with vibrational sum frequency generation (SFG) and THz-IR absorption spectroscopies. We show that water at the interface with a series of weakly interacting materials is organized into a two-dimensional hydrogen-bonded network (2D-HB-network), which is also found above some macroscopically hydrophilic silica and alumina surfaces. These results are rationalized through a descriptor that measures the number of "vertical" and "horizontal" hydrogen bonds formed by interfacial water, quantifying the competition between water-surface and water-water interactions. The 2D-HB-network is directly revealed by THz-IR absorption spectroscopy, while the competition of water-water and water-surface interactions is quantified from SFG markers. The combination of SFG and THz-IR spectroscopies is thus found to be a compelling tool to characterize the finest details of molecular hydrophobicity at aqueous interfaces.
水相界面的疏水性/亲水性从分子水平上源于水-水和水-表面相互作用之间的微妙平衡。本研究通过密度泛函理论-分子动力学（DFT-MD）与振动和频产生（SFG）及太赫兹-红外吸收光谱学相结合来对其进行了表征。我们发现，与一系列弱相互作用材料接触的水会形成二维氢键网络（2D-HB-network），在一些宏观亲水的二氧化硅和氧化铝表面也存在这种网络。我们通过一个描述符来解释这些结果，该描述符衡量界面水形成的“垂直”和“水平”氢键的数量，量化了水-表面和水-水相互作用之间的竞争。2D-HB-network 可通过太赫兹-红外吸收光谱直接揭示，而水-水和水-表面相互作用的竞争则可通过 SFG 标记物进行量化。因此，发现 SFG 和太赫兹-红外光谱学的组合是一种很有前途的工具，可以用来表征水相界面上分子疏水性的最细微细节。
