By Tyler Irving
Posted January 2011
The unique properties of wood and glass have fascinated sculptors and artisans for centuries. Now, an accidental discovery at the University of British Columbia has led to a new fusion of these materials that could have applications for everything from tinted windows to industrial catalysis.
Chemistry professor Mark MacLachlan and PhD student Kevin Shopsowitz were working to find new applications for nanocrystalline cellulose (NCC). NCC is produced by digesting waste wood with acid, and can be easily made on a large scale as a product of the forestry industry. The researchers hoped to use NCC to create a nanoporous material that could be used for hydrogen storage. First, they mixed a glass precursor (tetramethoxysilane, Si(OMe)4) with NCC in an aqueous solution. After evaporating the water, they heated the remaining glass film to burn out the tiny rod-shaped cellulose crystals, leaving behind pores.
To their surprise, the films were colourful and reflective (left). That’s because as the NCC dries, the rods form uniform layers like stacked logs, except that each layer is twisted slightly relative to the first (right). This results in helical pores with a repeating distance (pitch) that is similar to the wavelengths of visible light, resulting in a reflective material.
By changing the ratio of silica to NCC, the pitch of the helix can be easily adjusted. This in turn affects the wavelength of light reflected. “We can easily tune it, all the way from the infrared to the ultraviolet,” says MacLachlan. In fact, he has already received requests from companies interested in using his coatings to make windows that reflect infrared light, reducing cooling costs for large office buildings. The material could also be used to separate stereoisomers, catalyse reactions, build sensors, and even as jewelry. MacLachlan notes that the process only works at a narrow pH range, which by sheer coincidence was the one at which the NCC suspension arrived. The discovery came about “almost by our laziness, by not adding an acid or base catalyst to it,” he says. “It makes it beautifully simple.”
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