Ink-free printing and reusable paper


Ink-free printing and reusable paper

Paper with nanoparticles allows you to rewrite what is written on it many times – however, it still stores information for a very short time.

The printer ran out of paper again because someone decided to print out a book for the weekend? Moreover, the toner in the cartridge, as luck would have it, shows all the signs of moral and physical exhaustion? Here, of course, you can start to remember which side to put drafts into the printer so that it prints on the clean side, or how to shake the cartridge so that it is enough for a couple more printed pages. You can also try to teach your colleagues to read e-books.

Prussian blue is bleached by ultraviolet light and restores its color in air; titanium oxide acts as a photocatalyst. (Photo: Wang et al. ©2017 American Chemical Society.) Prussian blue also gives Van Gogh’s blue color. (Photo: Public domain.) Titanium dioxide is a common white dye. (Photo: Public domain.) ‹ › View full size

But you can try to solve the problem in a more inventive way – for example, as researchers from universities in China and the USA did, who created “eternal” paper that can be printed on many times, and without using ink at all. It cannot be said that such ideas have not occurred to anyone before – they have tried to create a similar technology more than once or twice, and even with some success.

The general idea here is to make a kind of reusable photo paper on which you can draw using light and then erase what you have drawn. However, every time some “but” arose that prevented the technology from leaving the walls of the laboratory into the world: either the paper turned out to be too sensitive to light or air, then there were too few cycles of high-quality “rewriting,” or the result turned out to be very expensive, and even dangerous for good health.

Chemists managed to solve all these problems at once with the help of Prussian blue and titanium oxide nanoparticles. Prussian blue is a blue pigment that has been known since the beginning of the 18th century and has a very wide range of applications. But the whole point of the invention lies not in the spectacular blue azure, but in nanoparticles.

Probably everyone has encountered ordinary titanium oxide in one way or another: some painted with titanium white, and others took tablets to which titanium oxide is added so that they have the canonical white color. As for titanium oxide nanoparticles, much more interesting applications are being found for them. For example, they are used as photocatalysts – the so-called semiconductor materials on the surface of which, when exposed to light, areas with high chemical activity are formed.

Activated photocatalysts can decolorize Prussian blue, converting it from an oxidized form to a reduced form. For the reaction to proceed most efficiently, nanoparticles must be of a certain size, shape, and, in addition, they must be integrated into a medium that will ensure their interaction with dye molecules. The right nanoparticles in the right environment can only be introduced into the porous structure of ordinary paper – and here we have real reusable paper for light printing.

It looks a little unusual, being a uniform blue shade due to Prussian blue. If an ultraviolet ray hits a sheet of such paper, the pigment will become discolored in the illuminated area, and then text or any other image can be printed here. However, the printed text is not stored for too long – no more than five days.

The fact is that if light transforms the blue pigment into a colorless form, then the oxygen in the air returns it back to its azure state, so the page of text gradually turns blue. However, the researchers managed to achieve an impressive number of rewrite cycles from the paper: with a print resolution of five microns, they used the same sample up to eighty times. The detailed results of the experiments were published in the journal Nano Letters.

But is such paper really needed in our time, when more and more information remains in digital form, without requiring any printed medium? On the one hand, the authors of the work emphasize the positive environmental effect: less paper consumption, less deforestation, less costs for recycling, including the extraction of paints. Which is definitely a good thing.

But on the other hand, such a short – at least for now – “lifetime” of a printed image greatly limits the scope of use of such technology. And what to do with “disposable” information typed, for example, in a newspaper: how to return those sheets that went into the hands of the reader? The only application that comes to mind in connection with such paper is its use in some secret espionage matters, if, of course, there are still old-school spies somewhere who prefer to work exclusively with paper media.

However, jokes aside, who knows, maybe it will actually be possible to find a special niche for such technology in the modern world.

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Gerald Russell

a passionate mechanical engineering student at the University of Technology of Compiegne. With a thirst for knowledge and a curious mind, Gerald dives into the depths of programming, immersing himself in the world of code. As a technology enthusiast and self-proclaimed mad engineer, he revels in pushing the boundaries of what's possible. Inspired by his deep fascination with technology, Gerald ventured into the realm of entrepreneurship, founding a tech startup that aims to revolutionize the industry. Driven by his insatiable curiosity and relentless ambition, Gerald continues to shape his path, forever driven by the pursuit of innovation and the desire to make a lasting impact.