State Key Laboratory of Nonlinear Mechanics, Institute of Mechanics, Chinese Academy of Sciences, Beijing 100190, China.
State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, China.
J Chem Phys. 2018 Feb 14;148(6):064704. doi: 10.1063/1.5010991.
The formation of gas bubbles presents a frequent challenge to microfluidic operations, for which fluids are geometrically confined to a microscale space. Here, to understand the mechanism of nucleating gas bubbles in microfluidic devices, we investigate the formation and stability of nanobubbles in confined solutions. Our molecular dynamics simulations show that while pinning of the contact line is a prerequisite for the stability of surface nanobubbles in open systems that can exchange gas with surrounding environment, in confined solutions, stable nanobubbles can exist even without pinning. In supersaturated condition, stable bubbles can be found in confined solutions with acute or obtuse contact angle, depending on the substrate hydrophobicity. We also demonstrate that when open to the bulk solution, the stable nanobubbles in closed systems would become unstable unless both supersaturation and pinning of the contact line are satisfied. Our results not only shed light on the design of novel heterogeneous surfaces for generating nanobubbles in confined space with controllable shape and stability but also address the crucial effect of gas exchange with the surroundings in determining the stability of nanobubbles.
气泡的形成给微流控操作带来了频繁的挑战，因为在微尺度空间中，流体受到几何限制。在这里，为了理解微流控装置中气泡成核的机制，我们研究了受限溶液中纳米气泡的形成和稳定性。我们的分子动力学模拟表明，虽然接触线的钉扎是开放系统中表面纳米气泡稳定性的前提，该系统可以与周围环境交换气体，但在受限溶液中，即使没有钉扎，稳定的纳米气泡也可以存在。在过饱和条件下，稳定的气泡可以存在于具有锐角或钝角接触角的受限溶液中，这取决于基底的疏水性。我们还证明，当与主体溶液开放时，除非同时满足过饱和度和接触线的钉扎，否则封闭系统中的稳定纳米气泡将变得不稳定。我们的结果不仅为在受限空间中生成具有可控形状和稳定性的纳米气泡的新型非均相表面设计提供了思路，还解决了与周围环境进行气体交换对纳米气泡稳定性的关键影响。
