[Soulja]

Hi,

Is there a widely available liquid or gas out there that'd rapidly expand (and subside) upon an "irritation" created by a simple electric circuit? For example, a tiny spark, a voltage change, a magnetic field change etc. Preferably the gas doesn't heat up substantially.

Thanks.

[Borek]

None that I am aware of. I do remember reading about polymers that were promising for kind of an "artificial muscle" application - but they were solid.

[Corribus]

Depends on what you mean by "rapid" and the amount of expansion you want. This property in solids is called piezoelectricity - application of mechanical force results in charging (and vice-versa - application of charging results in mechanical force). Because liquids (and certainly gasses) do not respond the same way to mechanical/sheer force as solids, this isn't something you usually associate with liquids and gasses. I believe piezoelectricity has been observed in some liquid crystals, but that may not be what you're looking for.

If electrical discharge causes a gas or liquid to heat, this would result in expansion..

[Enthalpy]

If the gas can get hot, yes, it's called an explosive. Zap, and boom.
Some serve in airbags for instance. These gases don't get so hot. But the reactants are astonishingly dangerous for a car.
Reversibly, that would be much more difficult. At least, you don't hope an effect stronger than the electricity you put in, do you? Energy conservation.

Just heating a gas with the electricity has decent efficiency. Not good, but better than piezoelectricity, magnetoelasticity and so on.