Explosive formation and dynamics of vapor nanobubbles around a continuously heated gold nanosphere
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| Lizenz | CC-Namensnennung 3.0 Unported: Sie dürfen das Werk bzw. den Inhalt zu jedem legalen Zweck nutzen, verändern und in unveränderter oder veränderter Form vervielfältigen, verbreiten und öffentlich zugänglich machen, sofern Sie den Namen des Autors/Rechteinhabers in der von ihm festgelegten Weise nennen. | |
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26
00:00
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Transkript: Englisch(automatisch erzeugt)
00:04
Hello, my name is Lei Hou. I'm going to tell you something about wiper bubbles with nanometer size, or nanobubbles, that we generated around gold nanoparticles in liquids and detected optically with nanosecond time resolution. We use a continuous laser at 532 nm to heat gold nanospheres and generate
00:25
nanobubbles, and we probe the nanobubbles by scattering a laser beam at 850 nm. The intensity of the scattered probe beam provides information about the dynamics of nanobubbles in the nanosecond regime.
00:41
First, we found that even under continuous heating, nanobubbles form and collapse very rapidly in an inertia-limited process we call explosive. The duration of one bubble is about some tens of nanoseconds. Many cycles of such fast bubble events repeat at a rate of a few MHz as shown here.
01:03
From the time dependence of this nanobubble instability as shown in this red curve, we propose that the liquid layer surrounding the nanosphere first must become overheated. Then the nucleation of a bubble is followed by evaporation of the overheated liquid and expansion of the bubble.
01:23
The expansion is barely resolved by our detector and appears to be determined by inertia. We therefore propose that this phenomenon is similar to explosive boiling previously observed in microscopic experiments. Second, within a narrow range of heating power, the nanobubble becomes very sensitive to weak local perturbations such as acoustic waves.
01:47
Here we showed an example of echo trigger nanobubbles when the heating power is constant but above some critical power. We average a number of these bubble events by taking the half-maximal of the red edge and obtain the red curve shown here.
02:03
Besides the first peak of fast bubble formation and collapse, we can observe a shoulder and sometimes a second peak appearing at well-defined delays after the first peak. We attribute these to the echoes of sound waves released after the first explosion reflected by glass-oil interfaces.
02:22
First between glass light and immersion oil, second between immersion oil and friendliness of objective. The reflected sound wave can modulate the bubble signal or even trigger a second or third explosion. These observations suggest that the nanobubble could serve as a two-way transducer between optical and acoustic
02:45
waves and could form the basis of an acoustic reader similar to those working with electromagnetic waves. In summary, we optically generate and probe wafer bubbles with high time resolution on a single particle level.
03:01
We observe nanobubble instability even under constant heating. Weak perturbations like sound wave can trigger new bubbles. Our findings open the possibility of using a nanobubble as an acoustic sensor or to enhance coupling to acoustic waves in photo-acoustic microscopy. Thanks for watching.