Human civilization is inextricably linked to the application of light. The development of science and technology has expanded people’s application of sunlight and popularized artificial lighting. However, inappropriate light radiation can also cause harm to quasi-health and well-being. As an important passage for outside light to enter the interior, windows play an important role in the light conditioning of buildings, vehicles and aircraft. There is an urgent need for windows with switchable optical functions to prevent or attenuate damage or interference to the human eye and photosensitive instruments by inappropriate light radiation.
In recent years, smart materials have achieved rapid development, and transparent materials that can provide intelligent light protection have attracted a lot of attention from researchers. In this case, liquid crystals (LCs), due to their rich responsiveness and unique optical properties, are considered one of the best candidates for advanced smart light protection materials.
The infrared thin film and crystal team of Harbin Institute of Technology proposed an intelligent light limiting assembly to achieve rapid light protection in complex light environments. The material is an adaptive optical material that responds quickly in complex environments and has the functions of light energy conversion, reflection of high-energy light or scattering path transfer. Through the bin-main effect, Michael’s scattering and Bragg reflection control mechanism on optical density, the programmable design of optical modulation is realized. It can be used in transient color change, visual imaging and flexible display.
The team published a review article in Light: Science & Applications under the title “Advanced liquid crystal-based switchable optical devices for light protection applications: principles and strategies.” Zhang Ruicong is the first author of this article, and Wang Tianyu and Zhu Jiaqi are the co-corresponding authors of this paper.
Figure 1 Intelligent light limiting assembly
In this paper, the optical protection application of liquid crystal-based switchable optics is comprehensively evaluated.
First, the specific light environment faced by LCD-based light protection and existing light protection strategies are discussed. According to the source, optical radiation can be divided into natural light and artificial light. Sunlight has a wide wavelength range (250nm-2500nm), large radiation angle changes, and large irradiation area. Lasers have the characteristics of high power, narrow wavelength and fast response. Other high-intensity lighting, such as sky lamps and spotlights, has the same response speed as lasers and a wider spectral range than lasers. Compared with traditional electronically controlled color-changing materials, liquid crystal materials show superiority in response time and protection bandwidth. Liquid crystal materials are excellent candidates for light protection because they offer significant advantages over traditional thermochromic materials in terms of stimulation temperature and visible light transmission.
Figure 2 Performance comparison of active/passive light protection technology
Secondly, several types of optical modulation principles based on liquid crystal materials are introduced. From the perspective of light energy, there are three types of light protection principles for liquid crystal materials:
1) convert incident light energy into other forms of energy;
2) transfer of incident light energy through the reflection path;
3) Transfer of incident light energy through the scattering path.
The characteristics, advantages and applications of these three types of light protection principles in light protection devices are discussed. However, in complex optical environments, comprehensive protection often requires the coupling of multiple mechanisms. Suggest light protection strategies in different light environments. When applying photoprotection devices on vehicles, it is necessary to pay attention to instantaneous light protection strategies, and for buildings, long-term light protection strategies are suitable.
Figure 3 (a) Traditional light barrier (b) Locally varying protection strategy
Windows in buildings are in a fixed position, exposed to sunlight for a long time and the window area is much larger than the light windows in vehicles. These different use cases place new demands on the light-proof equipment of buildings: low-cost and large-area manufacturing, long-term operation with low energy consumption, and infrared modulation capabilities. The researchers used flexible substrates instead of glass to create low-cost, large-area polymer/liquid crystal materials. To reduce energy consumption and further modulate the infrared, the researchers couple smart windows with solar cells to convert solar energy into electricity.
Figure 4 (a) Schematic diagram of the roll-to-roll preparation process (b) Operating principle diagram of luminescent solar concentrator (c) Solar cell (ST-PSC) and polymer/liquid crystal material (LCPC) coupling device
Summary and outlook
Although many types of liquid crystal light protection devices have been studied, their practical applications are still limited.
First, it is challenging to develop liquid crystal photoprotection devices that can adapt to long-term stable operation in different external environments. Mature liquid crystal light protection devices should have high UV radiation tolerance and electrochemical stability.
Second, there is a lack of liquid crystal light protection devices that can flexibly adapt to the needs of different external environments. In different scenarios, photoprotection devices of transparent materials need to have both active and passive protection strategies.
Third, these technologies face the challenge of expanding the scale of the device while ensuring good scale stability and uniformity during the commercialization process.
We expect the new generation of intelligent light limiting assemblies to completely solve the above problems. Fast response in complex environments, compatible with multiple mechanisms such as light energy conversion, reflection of high-energy rays, or scattering path transfer. It not only provides protection in multiple bands, but also reacts quickly in complex environments to meet the needs of switchable light protection materials and devices on buildings and traffic vehicles.
Lead author
Zhang Ruicong, the first author of this paper, is currently pursuing a doctoral degree at the Institute of Composite Materials and Structures, School of Astronautics, Harbin Institute of Technology, mainly engaged in the research of photoelectric thin films.
Corresponding author
Wang Tianyu, associate professor of the School of Energy Science and Engineering, Harbin Institute of Technology, youth director of the Chinese Society of Particles, has been engaged in the simulation research of multiphase flow flow and special protection of transparent parts for many years, and has been supported by the National Natural Science Foundation of China, Heilongjiang Provincial Department of Science and Technology, China Academy of Aeronautics, etc., published more than 40 papers, and participated in the basic scientific research of national defense of the Bureau of Science, Technology and Industry for National Defense, the basic strengthening plan of the Science and Technology Commission of the Military Commission, the national key research and development plan and other projects.
Zhu Jiaqi, professor and doctoral supervisor of the School of Astronautics, Harbin Institute of Technology, Changjiang Scholar Distinguished Professor, National Outstanding Youth Fund, leading talent of the 10,000 Talents Program, expert in the field of key special projects of the Ministry of Science and Technology, equipment development department, expert in the field of scientific and technological innovation of the Bureau of Science and Industry, leader of the national defense science and technology innovation team, deputy director of the National Engineering Research Center for Efficient Welding New Technology. Mainly engaged in the research of crystals and thin films, he serves as the deputy director of the Surface Engineering Branch of the Chinese Mechanical Engineering Society, the deputy director of the Extreme Materials and Devices Branch of the Chinese Materials Research Society, the vice chairman of the Chinese Instrument Materials Society, the deputy editor-in-chief of Functional Diamond, Advanced Materials & Devices, and the editorial board member of Surface Technology, Journal of Synthetic Crystals, Chinese Surface Engineering, Low Temperature and Vacuum, Functional Materials, Materials Science and Technology, etc. He has won the China Youth Science and Technology Award, the Provincial Youth May Fourth Medal and other honors, won 1 second prize of the National Technological Invention Award, 1 National Patent Gold Award, and 2 first prizes of Heilongjiang Province Technological Invention Award. He is responsible for 6 scientific research projects of the National Natural Science Foundation of China (including 1 key), 2 key R&D projects, 3 basic national defense scientific research, 7 pre-research plans, and 3 military supporting projects. The results have been applied to a variety of key models and industrialized. HE HAS BEEN AUTHORIZED 82 INVENTION PATENTS (21 TRANSFERRED), PUBLISHED MORE THAN 200 ACADEMIC PAPERS IN WELL-KNOWN JOURNALS SUCH AS SCIENCE AND ADVANCED MATERIALS, PUBLISHED 2 ACADEMIC MONOGRAPHS AND 1 TRANSLATION. (Source: LightScience Applications WeChat public account)
Related paper information:https://doi.org/10.1038/s41377-022-01032-y
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