MOSCOW, February 16. /TASS/. Russian scientists from the St. Petersburg University of IT, Mechanics and Optics (ITMO) have reported the development of a colorless, non-toxic ink for use in inkjet printers. Instead of relying on dyes, the team exploited the possibility of creating interference color images on a page via inkjet printing of nanostructures. The study was published in ACS Nano journal, ITMO University told.

The colors produced with this method do not fade over time and are completely safe for the ecosystem.

Current technologies blend dyes - think CMYK or RGB - to print in color. But these substances can harm the environment. Some dyes are toxic to marine life or can react with disinfectants like chlorine and form harmful byproducts. An alternative to dyes involves changing the nanostructure of materials so that they reflect light in particular ways. In particular, color can be produced by light interference - the same phenomenon that is responsible for those vibrant colors that we see in soap bubbles or other thin films, where the thickness of the film determines the color.

In the new study, Alexander Vinogradov and his colleagues from the Laboratory of Solution Chemistry of Advanced Materials and Technologies (SCAMT) at ITMO University wanted to develop a printing method that relies on the deposition of multicolor interference layers using a simple inkjet printer. The researchers demonstrated that such layers can be created with high accuracy and without the need for high-temperature fixing. The key to this technology turned out to be the ability to control the even deposition of ink droplets on the surface and their consequent conversion into nanostructures of required thickness. This plays a crucial role as the color of the image may vary with a change of only a few nanometers in film thickness.

"What we achieved is the first application of nanocrystalline sol-gel systems for the production of controlled interference in thin films using colorless ink based on titanium dioxide," Vinogradov said. "Adjustable multilayer printing by controlling the film thickness allowed us to create optical nanostructures on the surface. These nanostructures provide the light interference, which results in visual coloration. Given the number of colors in the visible spectrum, the number of shades of the structures applied by an inkjet printer is virtually unlimited."

The work currently is at the proof-of-principle stage. Creating a vibrant color red with this interference approach, for instance, remains a challenge. However, the reported green color turned out to be the first that is both safe for the ecosystem and did not fade from UV exposure.