Transparent glass is "outdated", color-changing glass is here!

Produced by: Science Popularization China

Author: Ishimiya

Producer: China Science Expo

Who is the one who looks at his phone the first thing he does when he opens his eyes in the morning and the last thing he does before going to bed? Who is the one who uses a smartwatch to check his health indicators even though he is a "young man or young woman who never stands up and doesn't like exercise"? Many friends may exclaim, "I am the one who is heavily addicted to mobile phones and a "punk health-conscious person"!"

With the continuous advancement of technology, smart appliances such as smart phones, smart TVs, and smart watches have long been around us. The application of these smart technologies has made our lives more convenient and colorful. However, we have seen a lot of smart phones and smart watches, but have you ever seen smart color-changing glass?

Intelligent color-changing glass with various styles

Ordinary glass is usually colorless and transparent. Photochromic glass refers to glass whose color changes non-permanently under certain external conditions. At present, a variety of intelligent photochromic glass has entered the market, mainly including photochromic glass, electrochromic glass, thermochromic glass, mechanochromic glass, gaseous glass, etc. So, how do these glasses achieve intelligence?

Photochromic glass (Photo source: Veer Gallery)

Photochromic glass

Glass that changes color under light is called photochromic glass, which is usually achieved by adding photosensitive materials to the raw materials. The most common photosensitive materials are copper halide and silver halide.

When light shines on the glass, the silver chloride microcrystals distributed inside the glass decompose to produce silver, and a large number of microcrystals produce a large number of silver atoms, which aggregate to form silver colloid. Silver colloid has a strong ability to absorb light, so the light transmittance of the glass decreases and the color becomes darker.

After being protected from light, silver and halogen will recombine with each other, and the light transmittance of the glass will be enhanced again, and the color will become brighter.

Photochromic glass (Image source: Veer Gallery)

Electrochromic glass

Electrochromic glass generally changes color by applying an electric field. It is usually doped with electrochromic materials such as tungsten trioxide, tetrathiafulvalene and metal phthalocyanine.

When an electric field is applied, the ions inside the glass will enter the electrochromic layer. When the two combine, a chemical reaction will occur, causing the color of the glass to change. The magnitude of the voltage is closely related to the depth of the color. After the power is turned off, the glass can return to its original color. The absorption and transmission of light in electrochromic glass is adjustable.

In addition, the principle of electro-atomized glass is similar to that of electrochromic glass. Electro-atomized glass changes the transparency and atomization state of the glass by controlling the power supply. The atomized glass interlayer is equipped with a dimming film with liquid crystal material. Liquid crystal has fluidity. When powered on, the liquid crystal will induce electric charge, thereby generating electrostatic torque and arranging in a regular pattern, so the light transmittance is good and the glass color is transparent. When the power is off, the liquid crystal will quickly return to the state of scattered and irregular arrangement by its own properties, and the light transmittance will deteriorate, and the glass will appear atomized.

Thermochromic glass

Temperature changes can also cause glass to change color. When a smart nano-gel film is added to the inside of the glass, when the external temperature rises, the nanoparticles will absorb energy and arrange themselves regularly, while when the temperature drops, the arrangement of the particles will become disordered, and the light transmittance of the glass will also change accordingly.

Mechanochromic glass

Compared with the above three types of color-changing glass, the use of mechanochromic glass is relatively rare in life. The color of the glass can be changed by adding materials whose structure changes under the action of external force.

Studies have shown that photonic crystal hydrogels formed by embedding hydrophobic substances inside polyacrylamide hydrogels can change color under the action of external forces. Under the action of external forces, the glass composed of them can also change color.

Hydrogel (Image source: Veer Library)

Gas-chromic glass

When the glass is exposed to certain gases, it will also change color. Gas-induced chromic glass usually contains a gas-sensitive layer, which is composed of a thin layer of porous tungsten trioxide film covered on a metal plate.

Normally, glass is transparent, but when hydrogen is introduced, a chemical reaction occurs in the sensitive layer and the glass turns blue. The higher the concentration of hydrogen, the darker the color of the glass, which can achieve the effect of filtering infrared rays. At this time, if you want to make the glass transparent again, you only need to introduce oxygen to achieve it.

Photochromic glass (Photo source: Veer Gallery)

Unexpectedly, seemingly inconspicuous glass can also become a "chameleon". So some people may want to ask, what happens after it changes color? What can photochromic glass be used for? In fact, photochromic glass has a wide range of uses, from glasses that people wear on a daily basis to the design of the appearance of buildings.

Photochromic glasses

Some people may have noticed that the glasses are transparent indoors, but they become sunglasses when they are outdoors in the sun. In fact, the lenses of these color-changing glasses are made of photochromic glass. In addition to being able to act as sunglasses outdoors, the more important point is that color-changing glasses can effectively absorb and filter ultraviolet rays, thereby reducing or avoiding the damage of ultraviolet rays to human eyes.

Photochromic glasses (Image source: Veer Gallery)

Bathroom frosted glass

In the bathroom, you can often see glass that changes between transparent and atomized. This kind of glass relies on controlling the power supply to achieve the random change of transparency. If you install this kind of glass in your bathroom, you will no longer have to worry about privacy issues. In other words, if you install atomized glass on the windows of your home, then can you do without curtains?

Fogged glass in the bathroom (Photo credit: Veer Gallery)

Building color changing glass

Most of the color-changing glass in buildings is thermochromic glass, which does not require additional power control, but changes color under the influence of the environment. When the temperature of sunlight rises, the glass will become darker, and the infrared transmittance will decrease; when the temperature drops, the glass will become brighter, and the infrared transmittance will increase. Correspondingly, the solar energy obtained indoors will increase.

Therefore, thermochromic glass helps maintain a constant temperature indoors, thereby greatly improving the comfort of residents. At the same time, it can also save energy and protect the environment.

Building color-changing glass (Photo source: Veer Gallery)

In addition to the various uses mentioned above, smart glass can also be used in the design and manufacture of automobile and aircraft windows. I believe that in the near future, smart color-changing glass will be more widely promoted in all aspects of our lives. With the full support of various emerging technologies, we are moving towards a brighter future that is more intelligent and technological.

References:

[1] Wei Hongli, He Feng, Wang Ping. New progress in the research of inorganic electrochromic glass[J]. Glass, 2006, 33(1):4.

[2] Qi Shuai, Zeng Hongjie, Yu Hao, et al. Energy-saving performance evaluation of photochromic glass in buildings[J]. Bulletin of the Chinese Ceramic Society, 2022, 41(4):1177-1184.

[3] Wang Guoqing, Zheng Shaoyu, Wang Peiqing, et al. Research on a photochromic film for intelligent dimming of glass[J]. Information Recording Materials, 2012, 13(006):16-21.

[4] Long Hui, He Xiao, Tian Lu. A brief analysis of the preparation of thermochromic glass materials[J]. China Building Materials Science and Technology, 2015(2):2.