Tuning the pores of a new type of glass film causes different colors, but adding a drop of water
turns them transparent. (Credit: Nature/Kevin Shopsowit.)

A team at the University of British Columbia, led by Mark MacLachlan, says its the first group to make mesoporous chiral nematic structured silica films cast from a nanocrystalline cellulose template prepared from wood pulp. The group, which says it was inspired by iridescence of beetle shells, predicts these materials could be used as tuneable reflective filters in smart windows, as chiral catalysts in synthesis and even as optical sensing devices.

Their paper describing the material, which can be made to be free-standing with a high surface area, was published in yesterday’s online journal Nature.

According to Chemistry World, attaining chirality from mesoporous silica materials has been difficult until now. “Others tried it before, but it turns out that the pH range over which these structures are formed — without any disruption — is very narrow,” MacLachlan told the magazine. He says the sugar chains in the cellulose are what makes the materials chiral.

By varying the ratio of silica to cellulose during production, the researchers say they can alter the size and shape of the pore spirals within the material, thus making them reflect different colors. And, by filling the pores with water, the structure becomes essentially transparent.

They say they can design the film to reflect specific wavelengths across the visible and near-infrared spectrum. Thus, they could produce a material that reflects infrared light, yet appears to be clear.

Given these properties, the researchers say the film has potential as, for example, a window coating that allows sunlight in, but prevents heat-producing wavelengths from passing. The research team is also developing ways to use the material in semiconductors and stereospecific catalytic applications.