B.C. scientists make colour-changing glass
B.C. researchers have discovered how to make glass films that reflect different wavelengths of light — ultra violet, visible and infrared — creating brilliant iridescent colours and traditional transparent glass.
They say it is a finding that could help us conserve energy and make our cities more visually intriguing.
University of British Columbia chemist Mark MacLachlan says windows could be coated with the glass film so they reflect infrared light, which heats a building and taxes its air conditioning system.
Right now, chemicals are added to glass to tint windows and reflect light, but that can leave the interior of a building dark, necessitating the use of artificial lighting.
"And chemicals can bleach in the sunlight, but our materials won't bleach because no chemicals are involved," said MacLachlan. The researchers' procedure makes use of a renewable substance — wood cellulose.
In a paper published this month in the peer-reviewed journal Nature, MacLachlan and his team describe how they used nanocrystaline cellulose, the main component of pulp and paper, to create the glass films.
It is a multi-step process that begins with a mixture of water, cellulose and silicon, which is the main ingredient in glass. As the solution dries, the cellulose organizes itself into tiny rod-shaped crystals arranged in a spiral pattern.
"The way to visualize this is that the rods dry so that in one layer they are all more or less oriented in one direction. Then the next layer is similar, but slightly twisted relative to the first, then the next layer is slightly twisted relative to the second, and so on," MacLachlan said.
The researchers then burned off the cellulose crystals, leaving them with a glass film dotted with tiny holes the same size and organization as the crystals.
"Because the holes have the helical structure, the glass reflects light of different wavelengths," said MacLachlan. "We can easily tune the glass to reflect any wavelength from infrared, to visible, to ultraviolet. We can make beautiful thin films of silica that are coloured because of this structure."
The glass can be "tuned" to reflect light in much the same way that beetle wings do, producing brilliant jewel-like colours.
MacLachlan says that means the glass films could be used to coat walls and as people walk by, they would see different colours as light hits the wall from various angles.