Gelified water as a transparent insulator
A transparent insulator has obvious uses for solar collection and, windows. By Gelifying (jellifying?) it, you prevent any sort of convective flow of water, and heat can only be transferred through the mass of water by conduction.
Water has a conductivity of about 0.58 W/m-degree, so 20 cm thick sheet of gelled water has the u value of 2.8, the same as a double glazed window. You could use agar as the gelling agent so you know it is nontoxic, but I bet there is something more suitable.
In order to keep it transparent when it is frozen, you need to remove the dissolved gasses, or they come out of solution and form bubbles in the ice. That’s easy to do – just freeze the water, then thaw.
The really cool application would be solar collectors. Obviously it is easy to make a horizontal one. To make a vertical one, suppose you took a sheet of plastic, and fold it over itself once. Heat-seal the edges, so you have a big, flat pocket that can hold water (I don’t mean this as an actual construction method, just to explain what I am thinking) The problem is, if you fill it with water and try to put it upright, the gelled sheet of water will eventually flow to assume the same shape as if it was filled with liquid water, which is definitely not the sheet-like shape we want.
So you take 20 cm long plastic or wood rods, the diameter doesn’t matter much, and put them inside the pocket thing, and glue one end to one side of the pocket, and the other to the other side. The idea here is that the pillars prevent the sheets from getting further apart from each other. The diameter is enough to make sure the strength of the glue-plastic part is strong enough.
You could use vapor barrier or greenhouse plastic, and there is a product called “all plastics superglue” Lepage sells which would work fine for the gluing. It comes with and “activator” thing that is used to do provide a surface treatment for the plastic so you can glue to it effectively.
So there you go, it could be used to make a very big solar collector at a very low price. Put an insulated box behind it and you’re all set. I wonder about the possibility of putting a really big one like this on the south wall of a house here in Canada, and it could provide a way to heat the whole house all winter long. the problem is it’s pretty heavy, so it might make more sense to make it free-standing, if the wall is not strong enough (but maybe it is fine).
For windows I’m not sure how useful it is, but you could make a highly insulating window pretty cheaply with it, so it could be good for a super cheap passive house, instead of the ridiculously expensive low e triple glazed units. For just daylighting, maybe even just fill some old pop or wine bottles with it, and use them embedded lengthwise in the wall. Or, for larger windows that let you see outside normally, 2 thin layers of plastic where the glazing on a regular double glazed window is, but the intervening space has to be much thicker, of course. Or 2 panes of glass, I guess, it would still be cheap. The glue they use for aquariums would work fine.