Refer to soap bubbles and butterfly wings, the Chinese Academy of Sciences uses transparent ink to achieve color printing

Printers are currently difficult to replace office equipment, but do you know that it will cause many environmental problems?

The chemical processes used to produce pigments and inks are not environmentally friendly. A large number of color printing requires constant replacement of multiple ink cartridges, and many ink cartridges are lying in the garbage dump before they are exhausted. According to statistics, 1.1 billion ink cartridges are discarded every year, and it will take about 450 years to decompose naturally. A box of ink with residual ink pollutes an average of 60 cubic meters of water.

▲ Advanced photo printers will be equipped with multiple color ink cartridges. Picture from: Denisgomes

The many problems in the printing industry encourage researchers to invent other methods to create color images. Recently, researchers from the Institute of Chemistry of the Chinese Academy of Sciences proposed a method of printing "full-color structural color images" using transparent polymer inks. This method breaks through our inherent knowledge of color printing, and color ink is no longer needed to present different colors.

Structural color (structural color), also known as "physical color", is the color produced by the interaction between microscopic physical structure and natural light (such as scattering, interference, diffraction, etc.). It is completely different from the color rendering principle of "chemical color" .

Gorgeous rainbows and soap bubbles, colorful peacock feathers and butterfly wings. These colors that shine in the sun are structural colors that are widely present in nature.

▲ Picture from: Brocken Inaglory

Researchers from the Chinese Academy of Sciences modified the most common color printer-inkjet printer based on the principle of structural color. They used a polymer ink that is transparent to the human eye, and replaced paper that easily absorbs most liquids with glass with a hydrophobic surface. When the water-based ink drops fall, they will be repelled by the glass, forming a structure similar to a "mini dome".

Using the surface tension characteristics of liquid and the hydrophobic effect of glass, the printer can create micro-domes of different sizes and shapes, each of which reflects light of different wavelengths, making the human eye perceive different colors. By grouping thousands of images together, you can create larger full-color images that look like colored ink droplets sprayed onto paper.

▲ Picture from: GIZMODO

However, this effect only works on one side. When viewing the glass sheet from the other side, the ink is still transparent, which is actually very useful.

Birds face a high mortality rate when they pass through the city. In New York City, 90,000 to 230,000 birds die every year due to window collisions, which are invisible to them. In the future, the entire skyscraper can be covered by such glass panes, whether it is a large billboard or a bird-safe window, without obstructing the view of the interior.

▲ Picture from: Institute of Chemistry, Chinese Academy of Sciences

Researchers believe that through precise manipulation of the micro-dome shape and pattern structure, they can fully control the saturation, brightness, and other aspects of the color.

▲ This new printing method has high fidelity. Picture from: GIZMODO

This new structural color method is compatible with existing printers and may also help reduce printing costs because it only requires a single ink. In addition, these prints can resist light bleaching and have a much longer service life than dyes that fade over time. As long as the micro-dome structure is not destroyed, the color will always be as fresh and saturated as first sight, so it is a more environmentally friendly and stable color rendering method.

In 2015, researchers at Missouri University of Science and Technology also created an "inkless printer" based on the principle of structural color. They used lasers to make thousands of small holes in metal materials to produce the same microstructure as butterfly wings, but only a few colors such as gold, green, orange, cyan, magenta and navy blue can be revealed.

▲ Thin sandwich material with thousands of micropores. Picture from: GIZMODO

The more important issue is that the "inkless printer" can only work on a micro level. It uses a thin interlayer material-only 170 nanometers thick, composed of two layers of silver, with a layer of silicon dioxide in between. This full-color version of the Missouri University of Science and Technology logo is approximately one-billionth of a meter in size.

▲ Picture from: GIZMODO

However, this "inkless printer" was originally "not printing", but chose to devote itself to more subtle applications, such as creating advanced security marks invisible to the naked eye and realizing new types of information storage.

Grapes are not the only fruit.

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