One of the ways to reduce global warming is to increase energy efficiency. Our current energy systems are mostly very inefficient. This is true in our architecture, where windows are notoriously poor insulators. Glass has an R value of about 0.14, double pane windows insulated with an air space between panes achieves a 2. Fiberglass insulation is rated at 2-4 and rigid foam insulation is 7-8 and considered the best insulator for construction. The only problem is that foam is hardly transparent. Who doesn't like to look out the window on a sunny day?
The folks at the University of Colorado have come up with some creative organic chemistry to produce a thin film insulating material that is transparent. The good news is that it is not made of toxic compounds, but naturally occurring cellulose. When is the last time you peered through a tree? (of course if you have superpowers that question is irrelevant). This is where the clever chemistry comes in. This thin film only 1.5mm thick is called SiCellA. It can adhere to glass and gets an R rating of 5-9, at least a 40% improvement over double pane windows.
Here is how it works. This aerogel starts with wood cellulose which is a long chain compound made up of connected glucose molecules. Cellulose is very strong and fibrous because the covalent carbon chains are connected to each other by hydrogen bonds. (see chart). In order to make the opaque substance transparent, researchers removed the hydrogen bounds with an oxidizing catalyst to make it into a cloudy fluid. At this point a strong acid is added to create a gel in which the cellulose chains regain some of their hydrogen bonds. This gel is poured into a mold and immersed in a solvent to replace water molecules. The mold is dried to evaporate the ethanol leaving nothing but air (hence the name) and voila, a transparent film of cellulose is left behind. One problem remains, however. The aerogel is not waterproof--not good for a window insulator. That problem is solved by adding a silicon compound to the tails of COOH groups.
The process is apparently straight forward and scalable.Moreover the film is not fragile and can be made into sheets for use in manufacturing. The film is stable to 200℃ with no loss of clarity or insulation. In tests it transmitted visible in the range of 97-99% which is better than glass and haze of less than 1%. Aerogels have been used in advanced applications before such as the Mars rover, but have proven to be fragile and to strongly scatter light. This process appears to have overcome the drawbacks. Increased use of insulated glazing in buildings will allow greater thermal efficiency, solar heating and more natural lighting. US Person is willing to trade that one 1% for a healthier planet.
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| treated window on campus, credit Nature Energy |