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Speaking of rainbow-colored chocolates, you think to yourself: what's so strange about that? Now that you have pigments and other additives, what kind of chocolate you want to make is not easy?

Speaking of rainbow chocolate, do you have rainbow-shaped chocolates (top) or colored chocolates (bottom)? | Pixabay, but scientists really think it is not that simple. One day, food scientists, materials scientists and physicists met in the hallway, and they talked about the chocolate that is common in daily life during the break. So they thought: is it possible to turn the chocolate itself into color without using any pigments or additives?

Chocolate is made from products of cocoa beans: cocoa butter and cocoa powder. Except for white chocolate without cocoa powder, ordinary chocolate itself is brown. Therefore, it is impossible to change the color of cocoa powder itself, so we can only work on the surface of chocolate.

After a variety of attempts, the scientists succeeded in creating this colorful flash on the surface of chocolate without adding any pigment. This seemingly magical "Rainbow Chocolate" changes into different colors under different angles of light.

The effect of the same chocolate from different angles is really colorful black. | | ETH Zurich / Giulia Marthaler |

Rainbow chocolate can vary with angle. ETH Zurich / Giulia Marthaler although this chocolate looks like a product of the wizarding world, its principle is not that difficult. Just warm the chocolate and pour it into a special 3D model. "anyone can do it at home." Said a maker who successfully made rainbow-colored chocolates. Because the principle behind this magic chocolate is the diffraction of light.

The rainbow color on the surface of chocolate is not formed by pigments and dyes, nor does it have any coating or other special ingredients, it is formed by the chocolate surface itself. This color can change with light and angle, called structural color (structural color), is formed by the scattering, interference and diffraction of light. This ever-changing color appears on the surface of soap bubbles, shells and many insect wings, which is the iridescent effect of the microstructure of the object itself on light.

The color light emitted by soap bubbles is different from the color of pigments and dyes and is called structural color. | Wiki, however, because the diffraction of light requires the reflectivity of the substance itself, if you want to make the chocolate surface glow in color, you must first ask a material scientist to make the chocolate surface very smooth and stable. This involves adjusting the temperature of chocolate.

The cocoa butter that makes up chocolate is a special kind of fat that has different crystal forms at different temperatures. For example, there are different forms of crystals in 17 ℃, 23 ℃, 34 ℃ and so on, and the temperature of chocolate is adjusted to make cocoa butter form a perfect cocoa crystal. We often see people slicing chocolates on marble slabs, actually adjusting the temperature.

In the process of adjusting the temperature, the unstable crystals in cocoa butter will all decompose and then recombine to form perfect crystals. When constantly stirred, the perfect chocolate crystals are connected to each other to form a tight network. Chocolate in such a perfect state has the best hardness and stability, and has a glossy shell.

Chocolate without temperature adjustment looks unstable and uneven, and has no silky taste. When the diffraction conditions were formed, the team began to consider doing some articles on the chocolate surface. they prepared a jagged, several-micron-wide groove mold and poured the chocolate inside to shape it. this is equivalent to engraving a diffraction grating on the chocolate surface.

The diffraction of light is that when the light wave encounters an obstacle, it deviates from the path of straight line propagation, and bends and scatters. Taking single-slit diffraction as an example, when a light wave passes through a large gap, it is equivalent to passing through countless small slits, and the light source in each slit is like a pebble thrown into the water, with ripples in a circle. These ripples are superimposed on each other, resulting in the bending and scattering of light.

A schematic diagram of the Huygens principle. A wave diffracts when it encounters an obstacle. These light waves superimpose each other like water waves, which leads to the bending and scattering of light. | when Wiki is reflected, the diffraction of light is the same, and the superposition of light waves can also occur. When white light shines on the reflector, the white light is dispersed into different colors, showing the effect of a rainbow. The most common example in our lives is CD-ROMs. The seemingly smooth surface of the optical disc actually contains a spirally distributed fine track, and the optical disc information is recorded in the track. This forms a circular reflection grating, which causes the white light to be decomposed into the rainbow color that we see with the naked eye.

The fine track on the surface of the optical disc forms a reflection grating. | the surface of Youtube@Applied Science rainbow chocolate should also be engraved with jagged striped tracks, resulting in a color effect similar to that of a CD.

In addition, the diffraction effect is related to the wavelength of light. If you want to have obvious diffraction on the chocolate surface, the distance between the sawtooth and the wavelength of light is similar. The wavelength range of visible light is generally 0.36-0.4 μ m ~ 0.76-0.83 μ m. The researchers chose the width of the jagged groove mold of chocolate in a few microns to make the reflected light diffracted obviously, thus giving rise to the magical "rainbow chocolate".

Speaking of engraving parallel grooves, the seemingly magical phenomenon of ↑ structural light in my brain is not rare, but it is often ignored by us. For example, the scales on a butterfly's wings, when we put it under a microscope, we will find that the wing scales have many translucent thin films, which are filled with air, and this structure makes the light magical, forming brilliant colors that change with the angle.

Chameleons, blue butterflies and insects all have microstructures on their skin that scatter specific light and show brilliant colors. Web.archive.org in short, as long as you can successfully carve a pattern on the surface of chocolate that is uniform, parallel and spaced close to the wavelength of visible light, then rainbow chocolate is made successfully, and indeed everyone can give it a try, this is probably the best diffraction grating in the world.

The enterprise of Zurich University of Technology has made the mold of rainbow chocolate, pour the chocolate into the mold, can appear the effect of rainbow chocolate! (want to play) | morphotonix.com Chocolate: I have changed color and become stronger.

Reference: https://docs.qq.com/ doc / DU2R5ZG9mTWdrV1Rl

This article comes from the official Wechat account: bring Science Home (ID:steamforkids), by Skin

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