固液界面纳米气泡的研究

Studies on nanobubbles formed at solid/liquid interface

在经典热力学理论中 ,室温下水中纳米气泡被认为是不能稳定存在的。近年来随着对疏水表面研究的深入 ,越来越多的现象暗示固液界面存在纳米气泡 ,并引起疏水长程作用力。目前直接探测固液界面纳米气泡的最有力手段是AFM ,但它只能观察纳米气泡的形貌 ,无法对其进行直接定性 ,很有必要提供纳米气泡存在和来源的更直接证据。在云母表面进行乙醇和水替换形成纳米气泡 ,从成像条件和脱气对纳米气泡的影响两方面进行系统研究。不同成像模式和成像条件下AFM观察到的差异在一定程度上证明了观察到的就是纳米气泡。脱气实验结果表明 ,经脱气后乙醇和水形成纳米气泡的数量和概率明显降低 ,表明乙醇和水中溶解的气体是纳米气泡的来源 。

On conventional thermodynamic grounds nanobubbles have a high internal gas pressure and should be dissolved into the bulk solution. However, it has been proposed that nonameter-sized air bubbles on the hydrophobic surfaces immersed in water are responsible for the long-range attractions between hydrophobic surfaces. At present for its strongpoint of imaging with nanometer resolution and measuring force with sub-piconewton resolution, tapping-mode AFM imaging in fluid has provided visual evidence for the presence of nanobubbles at solid/liquid interface. Unfortunately except for morphological information and mechanical characteristics of nanobubbles, it is difficult for AFM to reveal qualitatively what observed are nanobubbles. In this study, by the exchange of ethanol and water, in a repeatable way nanobubbles were formed at hydrophilic mica/water interface. The influences of image conditions and de-aeration on nanobubbles were investigated. The nanobubbles were observed by tapping mode AFM in fluid, but were too fragile to be observed by using contact mode and susceptible to deformation and destruction by the force from tapping mode AFM. Degassing ethanol and water reduced the amounts and the formation possibility of nanobubbles. It is concluded that the dissolved gas was the origin of the nanobubbles on mica surface formed by the exchange of ethanol and water. Furthermore, the change of the amounts and the formation possibility of nanobubbles with the quantity of dissolved gas in liquid is a qualitative evidence of the existence of nanobubbles at solid/liquid interface.