Tortora Marco, Meloni Simone, Tan Beng Hau, Giacomello Alberto, Ohl Claus-Dieter, Casciola Carlo Massimo
Dipartimento di Ingegneria Meccanica e Aerospaziale, Università di Roma La Sapienza, Via Eudossiana 18, 00184 Roma, Italy.
Nanoscale. 2020 Nov 19;12(44):22698-22709. doi: 10.1039/d0nr05859a.
Surface nanobubbles are gaseous domains found at immersed substrates, whose remarkable persistence is still not fully understood. Recently, it has been observed that the formation of nanobubbles is often associated with a local high gas oversaturation at the liquid-solid interface. Tan, An and Ohl have postulated the existence of an effective potential attracting the dissolved gas to the substrate and producing a local oversaturation within 1 nm from it that can stabilize nanobubbles by preventing outgassing in the region where gas flow would be maximum. It is this effective solid-gas potential - which is not the intrinsic, mechanical interaction between solid and gas atoms - its dependence on chemical and physical characteristics of the substrate, gas and liquid, that controls the stability and the other characteristics of surface nanobubbles. Here, we perform free energy atomistic calculations to determine, for the first time, the effective solid-gas interaction that allows us to identify the molecular origin of the stability and other properties of surface nanobubbles. By combining the Tan-An-Ohl model and the present results, we provide a comprehensive theoretical framework allowing, among others, the interpretation of recent unexplained experimental results, such as the stability of surface nanobubbles in degassed liquids, the very high gas concentration in the liquid surrounding nanobubbles, and nanobubble instability in organic solvents with high gas solubility.
表面纳米气泡是在浸入式基底上发现的气态区域，其显著的持久性仍未得到充分理解。最近，人们观察到纳米气泡的形成通常与液固界面处的局部高气体过饱和度有关。Tan、An和Ohl推测存在一种有效势，它将溶解气体吸引到基底上，并在距基底1纳米范围内产生局部过饱和度，通过防止在气体流动最大的区域发生脱气来稳定纳米气泡。正是这种有效的固气势——而非固体与气体原子之间的固有机械相互作用——以及它对基底、气体和液体的化学及物理特性的依赖性，控制着表面纳米气泡的稳定性和其他特性。在此，我们首次进行自由能原子计算，以确定有效的固气相互作用，从而使我们能够识别表面纳米气泡稳定性及其他性质的分子起源。通过结合Tan-An-Ohl模型和当前结果，我们提供了一个全面的理论框架，尤其能够解释近期一些无法解释的实验结果，例如脱气液体中表面纳米气泡的稳定性、纳米气泡周围液体中极高的气体浓度以及在具有高气体溶解度的有机溶剂中纳米气泡的不稳定性。
