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I am trying to reduce surface tension in liquids by technical means, without adding surfactants. I currently have two approaches but I'm not sure that they will actually work:

1) creating bubbles inside the liquid that rise to the air-liquid interface and break surface tension

2) creating cavitation in the liquid using ultrasonication. I read somewhere that cavitation lowers surface tension, but I can't find the source any longer.

Are these approaches correct?

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I've never heard of bubbles or ultrasound reducing the surface tension of a liquid. The surface tension is a result of the interactions of the molecules in the liquid with each other and with the air. As such it operates on the molecular scale and it's hard to see how any macroscopic phenomenon like bubbles would affect it.

Surface tension certainly affects cavitation because the surface tension is involved in the bubble collapse. So for example if you add surfactants to change the surface tension it affects the cavitation threshold. But this doesn't work in the opposite direction i.e. cavitation won't change the surface tension.

Apart from changing the temperature I don't know of any way to change the surface tension of water that doesn't involve mixing something with the water.

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  • $\begingroup$ Bubblers are sometimes used to reduce the pain associated with bad landings while training in springboard and platform diving. I suspect though that this has more to do with (a) reducing the mass density of the material you hit and (b) giving some of the displaced liquid a place to go. $\endgroup$ – dmckee --- ex-moderator kitten Mar 21 '19 at 1:52

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