How could you externally control omnidirectional movement of a gas bubble in a liquid?

Factual Questions
1

See subject.

In some scenarios, only still liquid.

Some, thermoclines allowed.

Others, interfacial currents at any “thinness.”

Any other concepts? Need not be achievable at the moment. I thought of nano-flagella, or nano-things on the inside of the bubble paddling away, like those plastic spheres people stand in and “pedal” with their feet.

Any and all flow regimes are encouraged. I don’t understand fluid dynamics, but am interested, so throwaway explanations of why x is of interest and why it will or won’t work are always appreciated. I encourage reader-supplied, science-fiction technology if necessary to control the project.

Also chemical explanations or solutions.

Initial reason/thought for this post came to me during a common event in a bath: can a bubble of gaseous iron (is there gaseous iron?) in water be moved around by a magnet…

2

All you have to do is manipulate the gravitational field around the system. The bubble will move in the direction opposite the force of gravity.

3

standing waves.

4

You can have gaseous iron. You can have liquid water. Not sure if you can have both at the same time, though… Certainly not at normal pressure.

I’d never heard of a magnetic gas, but apparently there’s at least one. That’s at almost absolute zero, though (0.00015 K), so again no liquid water.

5

Iron in a gaseous state will not be magnetic - in a gas the magnetic moments of the atoms are free to flip, and the thermal energy will be much greater (at over 3000K) than any induced magnetic moment.

You can use external magnetic fields to manipulate small magnetic objects - researchers hope to use these techniques to allow magnetically tagged drugs to be directed accurately to tumors.

With other techniques, ultrasonics can be used to manipulate and levitate small droplets in air.

6

If you’re going to allow shells, optical tweezers will work. I know they work on polystyrene beads.