Chemists Develop Safer Electrochromic Inks

Estimated reading time: 10 minutes

Water as a solvent is much safer, but it can present other challenges. Conjugated polymers are produced in organic solvents and do not inherently dissolve in water. Also, films printed from water-based inks might wash out in the rain or smudge in high humidity.

Schmatz’s invention combines the best of both worlds by using an organic solvent and an aqueous solvent in phases.

First, the conjugated polymer is produced in an organic solvent to assure quality material is made. That’s also aligned with chemical industry practices.

“Chemical companies really do a lot of this kind of processing, and it’s advantageous to keep this as it is, so the companies can keep doing what they’re doing and add this product more easily,” Schmatz said.

But then Schmatz alters the conjugated polymer – the ink’s active ingredient, so to speak -- which is usually not water soluble, so that it will indeed dissolve in water.

“We embed a chemical trigger within the polymer. It’s activated through a high pH water wash, and that transforms the organic soluble polymer into a water soluble polyelectrolyte,” he said. “The reason we want to 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.”

Ultraviolet Cleaver

To make sure that the film doesn’t smear or run after printing and that it functions well when it’s completed, Schmatz cleaves off that added chemical trigger from the conjugated polymer by shining ultraviolet light on the electrochromic film.

The water-soluble chemical chain then becomes a simple residue that can be wiped or rinsed off. What’s left is a robust, pure conjugated polymer film, which can no longer dissolve in water or organic solvents.

Reynolds envisions electrochromic films on various materials, including some other than glass or plastic. “You could apply this to camouflage, for example, with the right textiles, and have a sensor connected to a battery, and have it switch the colors to match the changing lightness or darkness of a soldier’s surroundings.”

Aside from electrochromics, these conjugated polymers are also being explored for printed transistors, solar cells, chemical and bio-sensors, light emitting displays and bioelectronics. Reynold’s group has access to a number of delivery methods to test application of conjugated polymers.

“Georgia Tech is a focused engineering university and has application capabilities you can find right here,” Reynolds said. “The various methods of printing or spraying are here – airbrush, blade coater, ink jet. And if we don’t have something, we can build it here.”

Anyone who has a rear-view mirror that automatically dims blue in reaction to annoying high-beam headlights glaring from behind has seen an electrochromic film in action.

Image Caption: Samples show some of the colors researchers have produced in electrochromic polymers. The materials can be used for applications such as sunglasses and window tinting that can be turned on and off through the application of an electrical potential. (Credit: Rob Felt)

Now, chemists at the Georgia Institute of Technology have developed a new method to more safely and, by extension, easily produce these shear films, which change their color with the help of a tiny electric current. This could make them available to many industries that have not been able to feasibly use them before.

In manufacturing, electrochromic films are often coated onto other materials, such as the surface of a mirror, as inks. They are usually based in solvents that are flammable and have toxic fumes, making them unsuitable for many work settings that rely on printing and spraying machinery to apply colors.

Georgia Tech researchers have developed electrochromic film inks that are water-based, making them safer for diffuse application in settings where the kinds of safety precautions and protective equipment that are standard in handling volatile organic chemicals would be impractical.

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