MMaterialsgateNEWS 2017/08/18

Related MaterialsgateCARDS

Spray-on Electric Rainbows: Making Safer Electrochromic Inks

Credit: Rob Felt

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.

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.

Everyday environments

“Where people print is not always in chemically safe environments,” said John Reynolds, a professor in Georgia Tech’s Schools of Chemistry and Biochemistry and Material Science and Engineering. So Reynolds and the study’s first author Brian Schmatz, who came up with the water-based method, set out to make electrochromic film inks safer for everyday environments.

There were some hurdles to pulling it off. 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. Schmatz’s method also needed to be logistically and financially realistic for producers to implement.

The researchers published details on their solution and how it has met the criteria in the journal ACS Central Science on August 16, 2017. Should the chemical process progress to production, the future may see more windows, prescription glasses, or even textiles that switch between colors and shades of darkness with the click of a button or with the help of a light-detecting switch.

That’s how many self-dimming rear-view mirrors work: The high-beams of the motorist behind you hit a light sensor that applies a mild electric field to the mirror, and that activates the color-changing, or electrochromic, film, which switches to a darker tint.

Electrochemical rainbow

The Reynolds lab’s electrochromic films are made with conjugated polymers, colorful and electroactive organic molecules. They easily let go of a few of their more loosely attached electrons, and when they do, their colors shift.

If the colored films are on a clear surface, when the color vanishes, the surface becomes clear. The surface has to be conductive so that a small voltage (about 1 volt) can be applied to bump the electrons off the conjugated polymer or help them jump back on.

The tints don’t have to be gray, blue, brown, or otherwise straight-laced. “We can make any color,” Reynolds said.
‘Toxic,’ ‘carcinogenic’

Because of previous inks’ organic solvents, applying electrochromic films in the past has come with significant safety requirements. Their costs could become prohibitive if the job is big, say, if a company wanted to cover the windows of an office building with an electrochromic film.

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

Also, people may simply find the smell of an organic chemical in their workplace unpleasant. Examples of organic solvent smells most everyone has experienced are kerosene, gasoline, or rubbing alcohol.

Organic then aqueous

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.”

Source: Georgia Institute of Technology – 16.08.2017.

Investigated and edited by:

Dr.-Ing. Christoph Konetschny, Inhaber und Gründer von Materialsgate
Büro für Material- und Technologieberatung
The investigation and editing of this document was performed with best care and attention.
For the accuracy, validity, availability and applicability of the given information, we take no liability.
Please discuss the suitability concerning your specific application with the experts of the named company or organization.

You want additional material or technology investigations concerning this subject?

Materialsgate is leading in material consulting and material investigation.
Feel free to use our established consulting services

MMore on this topic

Credit: Photo by David Kelly Crow

Smart windows equipped with controllable glazing can augment lighting, cooling and heating systems by varying their tint, saving up to 40 percent in an average building's energy costs.

These smart windows require power for operation, so they are relatively complicated to install in existing buildings. But by applying a new solar cell technology, researchers at Princeton University have developed a different type of smart window: a self-powered version that promises to be inexpensive and easy to apply to existing windows. This system features solar cells that selectively absorb near-ultraviolet (near-UV) light, so the new windows are completely self-powered. "Sunlight is a mixture of electromagnetic radiation made up of near-UV rays, visible light, and infrared energy, or heat," said Yueh-Lin (Lynn) Loo, director of the Andlinger Center for Energy and the Environment... more read more

Nanophotonics team creates low-voltage, multicolor, electrochromic glass

Rice University's latest nanophotonics research could expand the color palette for companies in the fast-growing market for glass windows that change color at the flick of an electric switch. In a new paper in the American Chemical Society journal ACS Nano, researchers from the laboratory of Rice plasmonics pioneer Naomi Halas report using a readily available, inexpensive hydrocarbon molecule called perylene to create glass that can turn two different colors at low voltages. "When we put charges on the molecules or remove charges from them, they go from clear to a vivid color," said Halas, director of the Laboratory for Nanophotonics (LANP), lead scientist on the new study... more read more

Researchers in the Cockrell School of Engineering at The University of Texas at Austin have invented a new flexible smart window material that, when incorporated into windows, sunroofs, or even curved glass surfaces, will have the ability to control both heat and light from the sun.

Their article about the new material will be published in the September issue of Nature Materials. Delia Milliron, an associate professor in the McKetta Department of Chemical Engineering, and her team's advancement is a new low-temperature process for coating the new smart material on plastic, which makes it easier and cheaper to apply than conventional coatings made directly on the glass itself. The team demonstrated a flexible electrochromic device, which means a small electric charge (about 4 volts) can lighten or darken the material and control the transmission of heat-producing, near-infrared radiation. Such smart windows are aimed at saving on cooling and heating bills for homes... more read more

Artists, print designers and interior decorators have long had access to a broad palette of paint and ink colors for their work. Now, researchers have created a broad color palette of electrochromic polymers, materials that can be used for sunglasses, window tinting and other applications that rely on electrical current to produce color changes.

By developing electrochromic polymer materials in a range of primary and secondary colors and combining them in specific blends, the researchers have covered the color spectrum – even creating four shades of brown, a particularly difficult color 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 color through the application of low-voltage electrical current. Supported by BASF, the research is reported in the journal ACS Applied Materials & Interfaces. The research was done in the laboratory of John Reynolds... more read more

More on this topic:

MaterialsgateNEWSLETTER

Partner of the Week

Search in MaterialsgateNEWS

Books and products

MaterialsgateFAIR:
LET YOURSELF BE INSPIRED