New colour palette for glasses, windows
ATLANTA: Artists, print designersandinteriordecorators have long had access to a broad palette of paint and ink colours for their work.
Now, researchers have created a broad colour palette of electrochromic polymers, materials that can be used for sunglasses, window tinting and other applications that rely on electrical current to produce colour changes.
The researchers have covered the colour spectrum – even creating four shades of brown, a particularly difficult colour combination. The materials could be used to make sunglasses that change from tinted to clear in a matter of seconds, at the press of a button. Other uses could include window tinting, signage and even greeting cards that change colour through the application of low-voltage electrical current.
The research is reported in the journal ACS Applied Materials & Interfaces. The research was done in the laboratory of John Reynolds, a professor in the School of Chemistry and Biochemisty and the School of Materials Science and Engineering at the Georgia Institute of Technology.
“We’ve demonstrated the ability to create virtually any colour we want by mixing different electrochromic polymers, j ust like mixing paint,” said Anna Österholm, a research scientist in Georgia Tech’s School of Chemistry and Biochemistry and the paper’s first author. “Using a simple coating method or even inkjet printing, we can create films that change colour with the application of a voltage.”
The many colours that have been developed by Reynolds’ group over the years include magenta, cyan, yellow, orange, blue and green polymers that can be dissolved in common solvents. In addition, blends of these polymer solutions can be predictably mixed to target specific colours. The brown shades are created by combining cyanandyellowprimarycolours with orange and periwinkle-blue secondary colours.
Photochromicsunglasses,which darken in response to light using a silver halide reaction, are already
We’ve demonstrated the ability to create virtually any colour we want by mixing different electrochromic polymers, just like mixing paint. Using a simple coating method or even inkjet printing, we can create films that change colour with the application of a voltage.
– Anna Österholm, research scientist
on the market. But many of these lenses respond to ultraviolet wavelengths that are filtered out by car windshields, require several minutes to transition – and can’t be controlled by users. The passive switching time can be problematic for pilots, drivers, security officers or others who move quickly between light and dark environments.
“In contrast, by using electrochromic polymers, we can create devices that by pushing a button,canbeconvertedfromdark to clear,” said Österholm. “They are completely user-controlled, and it doesn’t matter whether they arebeingusedindoorsoroutdoors, in a vehicle or an aircraft.”
The electrochromic materials rely on a reduction-oxidation (redox) reaction triggered by the applicationofanelectricalpotential provided by a simple coin battery: a positive one volt causes the glasses to be clear, while a minus one volt switches to the colour. “Essentially, we are just charging and discharging the device, which is what causes the colour change,” explained Eric Shen, a postdoctoral fellowintheGeorgiaTechSchoolof Chemistry and Biochemistry.
“Anything that you would want to have change colour at the push of a button would be an application for these,” said Shen. “We have shown that we can switch them on and off thousands of times, and that we can shine strong light on them without causing degradation of the colour.”
Theresearchershaveusedsimple sprayandblade-coatingtechniques to create films of the colourful materials. They now are using ink-jet printing to create patterns and mix the polymers to create colours.
“The ink-jetting is very versatile when you want to make patterns or very fine features with these materials,”Shensaid.“Thefactthat the polymers are so soluble makes it quite easy to process them using anythingthatwouldspreadan ink.” — Newswise