Quantifying interfacial tensions of surface nanobubbles: How far can Young's equation explain?
Quantifying interfacial tensions of surface nanobubbles: How far can Young's equation explain?
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DOI：
10.1039/d1nr07428h
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发表时间：
2022-01-05
期刊：
影响因子：
6.7
通讯作者：
Yamaguchi，Yasutaka
中科院分区：
文献类型：
--
作者：
Teshima，Hideaki;Kusudo，Hiroki;Yamaguchi，Yasutaka
固-液界面上的纳米气泡在各种物理化学现象中起着关键作用，了解它们的独特性质是至关重要的。然而，由于缺乏可靠的计算方法，人们对它们的界面张力知之甚少。基于力学和热力学的观点，我们首次利用分子动力学(MD)分析方法对亚微米级氮气泡在石墨-水界面的液-气、固-液、固-气界面张力进行了量化。结果表明，即使对于不同半径的纳米气泡，Young方程也是成立的。我们发现，纳米气泡内的气体密度对液-气和固-液界面张力的影响不大。相反，固-气界面张力存在尺寸效应，即由于气体在固体表面的吸附，随着气体密度的增加，界面张力显著降低。然而，我们的定量评估也表明，当足迹半径大于50 nm时，气体密度对接触角的影响可以忽略不计，这是实验中观察到的典型范围，因此，实验中观察到的亚微米级表面气泡的平坦形状和稳定性不能仅用范德华作用引起的界面张力的变化来解释，即用没有引入钉扎效应的杨氏方程来解释。基于我们的分析，澄清了诸如研究系统的差异等其他因素需要解释未解决的开放问题--这是对MD模拟中的纳米气泡超密、非平坦和稳定而没有钉扎的令人满意的解释。
Nanobubbles at solid–liquid interfaces play a key role in various physicochemical phenomena and it is crucial to understand their unique properties. However, little is known about their interfacial tensions due to the lack of reliable calculation methods. Based on mechanical and thermodynamic insights, we quantified for the first time the liquid–gas, solid–liquid, and solid–gas interfacial tensions of submicron-sized nitrogen bubbles at graphite–water interfaces using molecular dynamics (MD) analysis. It was revealed that Young's equation holds even for nanobubbles with different radii. We found that the liquid–gas and solid–liquid interfacial tensions were not largely affected by the gas density inside the nanobubbles. In contrast, the size effect on the solid–gas interfacial tension was observed, namely, the value dramatically decreased upon an increase in the gas density due to gas adsorption on the solid surface. However, our quantitative evaluation also revealed that the gas density effect on the contact angles is negligible when the footprint radius is larger than 50 nm, which is a typical range observed in experiments, and thus the flat shape and stabilization of submicron-sized surface bubbles observed in experiments cannot be explained only by the changes in interfacial tensions due to the van der Waals interaction-induced gas adsorption, namely by Young's equation without introducing the pinning effect. Based on our analysis, it was clarified that additional factors such as the differences in the studied systems are needed to explain the unresolved open issues – a satisfactory explanation for the nanobubbles in MD simulations being ultradense, non-flat, and stable without pinning.