Comments from Ionic fluid experts welcome!!
All this balloon talk reminds me of something else I thought of last week which got lost in a hectic weekend.
I have a colleague who makes nanocrystalline porous films and I wondered if these could be used to make a truly UV-transparent material for our balloon radiobiology experiments. Even quartz for instance absorbs more and more into the UVC at any mechanically feasible thickness. It's no longer transmitting a representative solar spectrum.
I wondered if you could seal the pores with a very, very thin film of quartz, cyclo-olefin etc - something nice and UV friendly and even more so due to being extremely thin. The pore structure would provide physical support, and the pores would be wider than half the wavelengths of UVC, and so wouldn't interfere with transmission. For that matter they would be
bigger than half a wavelength of any part of the solar visible spectrum of any possible biological relevance.
I had also wondered if you could seal the pores with a liquid, which would wick into the pores, but I couldn't work out how you'd stop it boiling off at high altitude.
My colleague gently poured cold water on the thin film idea, saying it was in fact very hard to do; the thickness and coverage is very variable.
However, he hit upon the same idea as me - a wicking liquid - but as a highly capable chemist he knew which to use, at least conceptually: An ionic fluid. These can be long and complex molecular chains and as such essentially have no vapour pressure, hence no evaporation. Again, since they
are long and complex, they have short-range order and are unlikely to absorb in the UV.