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Home > News > Industry News > Electro-colour-changing ink is.....

Electro-colour-changing ink is printed with water

  • Author:Ella Cai
  • Release on:2017-08-18
Georgia Tech chemists have developed water-based electrochromic film inks for colour-change applications such as auto-dimming rear-view car mirrors.

“There were some hurdles to pulling it off,” said GaTech. “The finished product had to electrically operate comparable to films that are applied in an organic solvent, and also be water-resistant in spite of the water-based production.”

The team of Professor John Reynolds is behind the development, using colorful and electroactive conjugated polymers – organic molecules that easily let go a few of their more loosely attached electrons, changing colour in the process. “We can make any colour,” Reynolds said. The change requites around a volt.

“Most research labs use chlorobenzene as a solvent. It’s pretty toxic. It’s carcinogenic, slightly volatile as well,” said lab member Brian Schmatz, who came up with the process. “So, it’s not something people want to work with at scale.”

Conjugated polymers have to be produced in organic solvents and do not inherently dissolve in water, said GaTech.

So after maunfacture, Schmatz adds a chemical chain – which he describes as a ‘chemical trigger’ – to the polymer molecule. When activated by a high pH water wash, the trigger transforms the polymer into a water-soluble polyelectrolyte. “We do all of this is so we can produce the polymer in an organic solvent, but then print the polymer from a water-based ink,” he said.

Once printed as an electrochromic film, ultra-violet light is used to cleave-off the trigger. “The water-soluble chemical chain then becomes a simple residue that can be wiped or rinsed off,” said Schmatz. “What’s left is a robust, pure conjugated polymer film, which can no longer dissolve in water or organic solvents.”

Lab leader Reynolds envisions electrochromic films on glass, plastics and other materials. He has previously demonstrated technology for self-dimming sun glasses.

“With the right textiles, you could apply this to camouflage, and have a sensor switch the colors to match the changing lightness or darkness of surroundings.”