Study on the Formation and Properties of Trapped Nanobubbles and Surface Nanobubbles by Spontaneous and Temperature Difference Methods

Abstract

Trapped nanobubbles are gas domains trapped at nanopits on the solid−liquid interface. This is different from surface nanobubbles that usually form at the smooth surface. Herein, both trapped nanobubbles and surface nanobubbles formed on the nanopitted polystyrene film were studied by a spontaneous formation method and a temperature difference method. Trapped nanobubbles behave more flexibly than surface nanobubbles under different scanning loads. The nanopits under trapped nanobubbles appear after being subjected to large force scanning, and both trapped nanobubbles and surface nanobubbles can recover after reducing the scan load. The contact angles of the two kinds of nanobubbles were calculated and were found to be approximately constant. Configurations of trapped nanobubbles including under the pit mouth, protruding out but pinning at the pit mouth, and protruding out and extending around the pit mouth were experimentally observed. Gas oversaturation in the liquid after replacing the low-temperature water with high-temperature water was evaluated and was found to be a key factor for nanobubble formation and led to trapped nanobubbles protruding out and extending. Our study should be helpful in understanding the formation mechanism and properties of trapped nanobubbles and surface nanobubbles, and it will also be useful for further research on the control of nanobubble distribution.

Estimating the Pinning Force of Surface Nanobubbles Based on Trapped Nanobubble Protruding

“…During trapped nanobubble nucleation, the triple-phase contact line will first experience a change from the bottom of the nanopit to pin at the pit mouth (form 1); after reaching the stage of pinning at the pit mouth (form 2), the trapped nanobubble will experience an unstable state in the course of expansion, and then, the pinned contact line begins to extend around the pit mouth and at last reach form 3. In our experiments, the observed trapped nanobubbles are usually in form 3, which has also been observed in our recent experimental study . This means that the trapped nanobubbles have extended around the pit mouth.…”

Probing the “Gas Tunnel” between Neighboring Nanobubbles

“…43−46 The process of nanobubble formation on nanopits has been investigated in one of our recent works. 38,45 It is found that the size of nanopits has an important influence on the entrapped nanobubbles.…”

“…According to the crevice model proposed by Atchley and Prosperetti, the gas molecules near the liquid–solid interface can be entrapped in crevices or pits and then grow by gas expansion or by gas diffusion and at last protrude out and nucleate surface nanobubbles. This indicates that surface structure is also an important factor for bubble nucleation. − The process of nanobubble formation on nanopits has been investigated in one of our recent works. , It is found that the size of nanopits has an important influence on the entrapped nanobubbles.…”

“…During scanning, the AFM tip disturbs the equilibrium of the system, and there might exist discrepancy between scattering studies and AFM studies; i.e., there were no nanobubbles observed in some scattering studies while AFM studies in many cases show nanobubbles. − Although AFM measurement is an intrusive technique, it has generally been accepted that surface nanobubbles are not a consequence of tip perturbation . The tip–bubble interaction has been widely investigated, such as the movability and coalescence of nanobubbles under the AFM tip disturbance, , wetting properties of AFM tips, the effects of tip–bubble interaction, , and different AFM modes on the morphology of surface nanobubbles. − However, it is still not clear how the pinned nanobubbles interact with each other under large scanning force. On one hand, if there are gas tunnels between surface nanobubbles as report in ref , a dramatic change of the gas molecule number in nanobubbles caused by tip–bubble interaction will affect its neighboring bubbles and thus lead to changes in their morphology.…”

Exceptional Mineral Scaling Resistance from the Surface Gas Layer: Impacts of Surface Wetting Properties and the Gas Layer Charging Mechanism

“…This solution injection is considered the start of the experiment (i.e., t = 0). The sudden temperature change in the solution near the surface induces initial gas bubble nucleation due to the gas solubility decrease associated with temperature . After 10 min, solution 2 with bulk gas solubility S gas,2 , was injected also at 50 μL min –1 into the flow cell at 50 °C.…”