| > What does it mean in thermodynamic terms? Isn't there a fixed amount of energy per mass that it takes to convert liquid water into vapor? Yes. The rest of the energy comes from the bulk water/hydrogel in other words, the bulk water is cooled by this process. What’s happening is that energy is sloshing around between various degrees of freedom of the system (the temperature of the system is not zero). When it sloshes is such a way that a water molecule near the surface has more kinetic energy than the bond strength between it and the bulk, that molecule evaporates. Since the “sloshed” molecule has greater-than-average energy just before evaporation, the average energy of the remaining bulk water is reduced (the bulk cools). But the interesting thing here is that it seems that they have found a resonance where the photon will not just cause the water molecule to evaporate “early” and also carry with it more excess energy than the phone came in with (hence having an evaporation rate 2x expected). I wonder if this has something to do with the hydrogel causing the water to behave more like a solid, and enabling some kind of phonon-photon coupling process that isn’t supported in pure bulk water > Why does it matter that the energy comes from light? Practically, because they want to make a solar desalination system (though this just raises the question of how do you get monochromatic green light from the solar spectrum). Scientifically, because it is interesting that the photon will trigger a water molecule to take off with more energy than the photon. Also, it feels entropically weird. |