Molecular hydrophobicity at a macroscopically hydrophilic surface
Molecular hydrophobicity at a macroscopically hydrophilic surface
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DOI：
10.1073/pnas.1819000116
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发表时间：
2019-01-29
影响因子：
11.1
通讯作者：
Backus, Ellen H. G.
中科院分区：
文献类型：
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作者：
Cyran, Jenee D.;Donovan, Michael A.;Backus, Ellen H. G.
水和硅酸盐之间的界面是普遍存在的，并且与地球化学、大气化学和色谱法等相关。在二氧化硅表面的水组织的分子水平的细节是重要的基本了解这个接口。虽然二氧化硅是亲水性的，但已在二氧化硅表面鉴定出弱氢键合的OH基团，其特征在于高O-H伸缩振动频率。在这里，通过结合实验和理论的表面选择性振动光谱，我们表明，这些OH基团起源于非常弱的氢键水分子在名义上亲水性二氧化硅界面。这些OH基团的性质与通常在疏水表面观察到的那些非常相似。分子动力学模拟表明，这些弱氢键的水OH基团指向与他们的氢原子对当地的疏水性网站组成的氧桥的二氧化硅。这些分子疏水位点的密度增加，从弱氢键水OH基团的增加中可以看出，与宏观接触角增加相关。
Interfaces between water and silicates are ubiquitous and relevant for, among others, geochemistry, atmospheric chemistry, and chromatography. The molecular-level details of water organization at silica surfaces are important for a fundamental understanding of this interface. While silica is hydrophilic, weakly hydrogen-bonded OH groups have been identified at the surface of silica, characterized by a high O-H stretch vibrational frequency. Here, through a combination of experimental and theoretical surface-selective vibrational spectroscopy, we demonstrate that these OH groups originate from very weakly hydrogen-bonded water molecules at the nominally hydrophilic silica interface. The properties of these OH groups are very similar to those typically observed at hydrophobic surfaces. Molecular dynamics simulations illustrate that these weakly hydrogen-bonded water OH groups are pointing with their hydrogen atom toward local hydrophobic sites consisting of oxygen bridges of the silica. An increased density of these molecular hydrophobic sites, evident from an increase in weakly hydrogen-bonded water OH groups, correlates with an increased macroscopic contact angle.