Development of self-healing lens material to prevent traffic accidents in self-driving cars

Safety issues of self-driving cars have emerged due to frequent self-driving traffic accidents. A self-healing lens material that can prevent car accidents that occur due to signal distortion by restoring scratches on the sensor surface of the self-driving car has been developed.

The Korea Research Institute of Chemical Technology (KRICT, President Lee, Young Kuk) research team led by Dr. Kim Jin Chul, Park Young Il, and Jeong Ji-Eun* and Prof. Kim Hak-Rin and Prof. Cheong In Woo in Kyungpook National University (KNU) developed a material that heals scratches on the sensor of an autonomous vehicle.
^{* Technology from「Can scratches on car surfaces disappear when exposed to sunlight? : A new self-healing coating material」, published in 2022, has been further developed to enable not only structural recovery but also functional recovery such as recovery of an optical signal.}

When this self-healing optical material is used in the sensor of an autonomous vehicle, it is expected that the life expectancy of the product can be increased and future technology that can prevent malfunctions due to surface damage can be secured.

A lens is a tool that collects or disperses light and is used in many everyday optical devices such as cameras, cell phones, and glasses. However, if the lens surface is damaged by a scratch, the image or optical signal received by the optical device can be severely distorted.

Recently, traffic accidents caused by recognition errors and malfunctions of vision systems* such as LiDAR sensors and image sensors of self-driving cars have repeatedly occurred. As a result, confidence in the safety of self-driving cars is rather low**.
^{* LIDAR sensors and image sensors that acts as the ‘eyes’ of an autonomous vehicle
** The results of a survey by the American Automobile Association showed that the number of respondents who were afraid of using self-driving cars increased by 13% from 55% in 2022 to 68% in 2023.}

The KRICT-KNU joint research team developed a transparent lens material that can remove scratches on the sensor surface within 60 seconds when focused sunlight is irradiated using a simple tool such as a magnifying glass.

Because self-healing is favorable when molecular movement within the polymer is free, flexible materials are generally advantageous in securing excellent self-healing performance. However, lenses or protecting coating materials are made of hard materials, and thus it is very difficult to impart a self-healing function. To solve this problem, the research team combined a thiourethane structure, which is already being used as a lens material, and a transparent photothermal dye* to design a 'dynamic chemical bond' in which the polymers repeat disassembly and recombination under irradiation of sunlight.
^{* A dye that converts light energy into heat energy}

In particular, the developed transparent organic photothermal dye can selectively absorb light of a specific near-infrared wavelength (850-1050 nm) without interfering with the visible light region (350-850 nm) used for image sensors and the near-infrared region (~1550 nm) used for LiDAR sensors.

When sunlight is absorbed by photothermal dyes, the surface temperature of the developed lens material rises as the light energy is converted into thermal energy. Subsequently, the increased surface temperature makes it possible to self-heal a surface scratch by repeating the dissociation and recombination of chemical bonds in the polythiourethane structure.

The developed lens material shows perfect self-healing even when scratches cross each other, and provides excellent resilience, maintaining 100% of the self-healing efficiency even if the process of scratching and healing at the same location is repeated more than five times.

Dr. Lee Young Kuk, president of KRICT, said, “This technology is a platform technology that synthesizes self-healing lens materials using both an inexpensive high-refractive polymer material and a photothermal dye. It is expected to be widely used in various applications such as autonomous vehicle sensors as well as glasses and cameras.”

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 KRICT was established as a government-funded research institute in 1976. It has played a leading role in the development of the national chemical industry as it developed technologies for chemical and related fields of convergence, transferred chemical technologies to industries, produced professionals in the chemical field, and provided tremendous support for a variety of chemical infrastructures. Now we promise to reach new heights in chemistry and chemical engineering and continue our role in facilitating increased use of the knowledge from research. For more information, please visit KRICT’s website at https://www.krict.re.kr/eng/

This study was supported by the New Career Researcher Program of the National Research Foundation of Korea and Korea Research Institute of Chemical Technology (KRICT). The research was published in the Feb 2023 issue of 'ACS Applied Materials and Interfaces'(IF: 10.383), an international scientific and technological journal.