Li Dayong, Zeng Binglin, Wang Yuliang
School of Mechanical Engineering , Heilongjiang University of Science and Technology , No. 2468 Puyuan Road, Songbei district , Harbin 150022 , P. R. China.
Robotics Institute, School of Mechanical Engineering and Automation , Beihang University , No. 37 Xueyuan Road, Haidian district , Beijing 100191 , P. R. China.
Langmuir. 2019 Nov 26;35(47):15029-15037. doi: 10.1021/acs.langmuir.9b02682. Epub 2019 Nov 13.
Surface nanobubbles are the main gaseous domains forming at solid-liquid interfaces, and their abnormally long lifetime (stability) is still an open question. A hypothesis "gas tunnel" was presented in a recent simulation study [ , (3), 2603-2609], which was thought to connect two neighboring nanobubbles and make the nanobubbles remain stable. Herein, we aim to experimentally investigate the existence of gas tunnel and its role in governing nanobubble dynamics. By using an atomic force microscope, mutual effects between different gaseous domains including nanobubbles, nanopancakes, and nanobubble-pancake composite on a PS substrate undergoing violent tip perturbation and their effects on the undisturbed neighbors were investigated. The pancake between two nanobubbles can behave as a visible gas tunnel under the tip-bubble interaction. Based on statistical analysis of volume change in the different gas domains, the concept of a generalized gas tunnel is presented and experimentally verified. Nanobubbles are surrounded by a water depletion layer which will act as a channel along solid/liquid surfaces for adjacent nanobubbles to communicate with each other. Moreover, the change in contact angle of nanobubbles with the concentration of local gas oversaturation was studied, and the equilibrium contact angle of nanobubbles is further verified experimentally.
表面纳米气泡是在固液界面形成的主要气态区域，其异常长的寿命（稳定性）仍是一个悬而未决的问题。最近的一项模拟研究[ ， （3），2603 - 2609]提出了“气体隧道”假说，该假说被认为连接两个相邻的纳米气泡并使纳米气泡保持稳定。在此，我们旨在通过实验研究气体隧道的存在及其在控制纳米气泡动力学中的作用。通过使用原子力显微镜，研究了在PS衬底上经历剧烈尖端扰动时不同气态区域（包括纳米气泡、纳米薄饼和纳米气泡 - 薄饼复合体）之间的相互作用及其对未受干扰邻居的影响。在尖端 - 气泡相互作用下，两个纳米气泡之间的薄饼可表现为可见的气体隧道。基于对不同气体区域体积变化的统计分析，提出并通过实验验证了广义气体隧道的概念。纳米气泡被贫水层包围，该贫水层将作为沿着固/液表面的通道，使相邻纳米气泡相互连通。此外，研究了纳米气泡接触角随局部气体过饱和度浓度的变化，并通过实验进一步验证了纳米气泡的平衡接触角。
