New Atlas: Water can evaporate with just light, no heat, says surprising study (newatlas.com)

submitted 11 months ago by kixik@lemmy.ml to c/science@lemmy.ml

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[-] Pons_Aelius@kbin.social 14 points 11 months ago

So for the new study, scientists at MIT set out to investigate what might be happening. After a few basic experiments, they suspected that light itself was causing the excess evaporation. The idea is surprising because water doesn’t really absorb light – hence why you can see through it to a decent depth if it’s clean.

To really check their hypothesis, the scientists placed a hydrogel sample in a container on a scale, exposed it to different wavelengths of light in sequence, and measured the amount of mass it lost over time to evaporation. The equipment was carefully controlled and the lights shielded to prevent any heat being introduced to the system and messing with the results.

One possibility: The hydrogel is absorbing the light and emitting it as heat to the water thus increasing the evaporation.

[-] porkins@sh.itjust.works 11 points 11 months ago* (last edited 11 months ago)

Yeah. It is odd that they did the experiment with hydrogel when the subject of focus is water itself. Then again, the water container could potentially absorb light and emit heat, which would also confound the result.

[-] nooneescapesthelaw@lemmy.ml 5 points 11 months ago

I think you might be underestimating these guys a little, however skepticism is a part of science.

Replication experiments are being done right now so we'll see what happens, but I'm sure they have adjusted for that

[-] mindbleach@sh.itjust.works 2 points 11 months ago

Anything clear should be about as non-light-absorbent as pure water. Glass, for example.

Or use a dielectric mirror and laser-light - so the overwhelming majority of monochromatic photons are reflected.

[-] porkins@sh.itjust.works 3 points 11 months ago

Interesting. Just not sure then why they need the extra polymers added. They should have at least done some rounds with just water.

I find it super fascinating that the most effective color happens to be that of chlorophyll.

[-] be_excellent_to_each_other@kbin.social 7 points 11 months ago* (last edited 11 months ago)

OK the relevant classes are many years behind me (and I don't work in a science field), but since photons are going to transfer some energy to any particle they interact with, how is this not effectively the same as evaporation with heat? This sounds like a tiny bit of radiant heat to me.

I would guess it's not or we wouldn't be discussing the article, but I'm not seeing the difference.

[-] nooneescapesthelaw@lemmy.ml 6 points 11 months ago

This article skips over a few points, heres the paper:

https://www.pnas.org/doi/10.1073/pnas.2312751120?url_ver=Z39.88-2003&rfr_id=ori%3Arid%3Acrossref.org&rfr_dat=cr_pub++0pubmed

So your idea seems plausible at first, but more information leads to the proposed photo molecular effect:

Illumination of hydrogel under solar or visible-spectrum light-emitting diode leads to evaporation rates exceeding the thermal evaporation limit, even in hydrogels without additional absorbers.

Also the absorption of both the water and gel are negligible

this post was submitted on 02 Nov 2023

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