Probing Internal Pressures and Long-Term Stability of Nanobubbles in Water
Probing Internal Pressures and Long-Term Stability of Nanobubbles in Water
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探测水中纳米气泡的内部压力和长期稳定性
DOI：
10.1021/acs.langmuir.0c03574
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发表时间：
2021
期刊：
影响因子：
3.9
通讯作者：
Xiaonan Shi, Shan Xue
中科院分区：
文献类型：
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作者：
Xiaonan Shi, Shan Xue
与大体积气泡相比，液体中的纳米气泡（NB）表现出许多有趣的性质，例如低浮力和高传质效率和反应性。然而，它仍然是难以捉摸的，为什么或如何散装NB在水中稳定，特别是，由于缺乏适当的方法或仪器，很难测量的NB的内部压力的状态。该研究采用高压气体通过疏水化陶瓷膜的注入来产生不同的气态NB（例如，N2，O2，H2和CO2），这与具有潜在内部低压和非冷凝气体的空化气泡不同。结果表明，增加注入气体压力（60-80 psi）和溶液温度（6-40 °C）都将气泡尺寸从约400 nm减小到200 nm，这通过从Young-Laplace方程和接触力学开发的两个独立模型来验证。特别是胶体力模型可以解释表面张力和表面电荷排斥对气泡尺寸和内压的影响。接触力学模型结合了通过原子力显微镜对尖端-气泡相互作用力的测量，以确定NB的内部压力和硬度（例如，杨氏模量）。胶体力平衡模型和我们的接触力学模型都产生了各种NB（120-240 psi）的内部压力的一致预测。所开发的方法和模型框架将有助于揭示NB的性质并支持NB的工程应用（例如，曝气或臭氧化）。最后，密封储存的散装NB可以稳定约一周，并在接下来的30-60天内逐渐降低浓度。
Nanobubbles (NBs) in liquid exhibit many intriguing properties such as low buoyancy and high mass transfer efficiency and reactivity as compared to large bulk bubbles. However, it remains elusive why or how bulk NBs are stabilized in water, and particularly, the states of internal pressures of NBs are difficult to measure due to the lack of proper methodologies or instruments. This study employed the injection of high-pressure gases through a hydrophobized ceramic membrane to produce different gaseous NBs (e.g., N2, O2, H2, and CO2) in water, which is different from cavitation bubbles with potential internal low pressure and noncondensed gases. The results indicate that increasing the injection gas pressure (60–80 psi) and solution temperatures (6–40 °C) both reduced bubble sizes from approximately 400 to 200 nm, which are validated by two independent models developed from the Young–Laplace equation and contact mechanics. Particularly, the colloidal force model can explain the effects of surface tension and surface charge repulsion on bubble sizes and internal pressures. The contact mechanics model incorporates the measurement of the tip–bubble interaction forces by atomic force microscopy to determine the internal pressures and the hardness of NBs (e.g., Young’s modulus). Both the colloidal force balance model and our contact mechanics model yielded consistent predictions of the internal pressures of various NBs (120–240 psi). The developed methods and model framework will be useful to unravel properties of NBs and support engineering applications of NBs (e.g., aeration or ozonation). Finally, the bulk NBs under sealed storage could be stable for around a week and progressively reduce in concentrations over the next 30–60 days.