UNIST Develops Technology to Reveal Hidden Images Using Only 'Wrinkles' Without Pigments

Kim Taesung's Team Develops Nano-Wrinkle Based Variable Structural Color Film
Anti-Counterfeiting and Responsive Display Applications, Published in Advanced Functional Materials

A technology that reveals graphic images on a transparent film using wrinkles, without any pigments, has been developed.

This is expected to contribute to the development of anti-counterfeiting and responsive display technologies.

A research team led by Professor Kim Taesung from the Department of Mechanical Engineering at UNIST announced on the 13th that they have developed a technology that can display or conceal color patterns, similar to traditional Korean Dancheong designs, by folding and unfolding nano-wrinkles formed on transparent films.

Professor Kim Taesung.

The developed technology utilizes the principle of structural coloration. Structural color appears when light is interfered by nanostructures. Chameleons and peacocks can display blue colors without blue pigment cells thanks to nanostructures in their skin cells or feathers.

The research team used these nanostructures to create wrinkles. Since the wrinkles only appear when the film is bent, the coloration can be shown or hidden, and by adjusting the spacing and height of the wrinkles, various colors can be produced.

To ensure that wrinkles only appear when the film is bent, the team devised a bilayer film structure. When a rigid film is placed on top of a flexible film, the difference in physical properties between the two layers causes nano-wrinkles to form on the surface of the rigid film when force is applied. This is similar to how wrinkles appear on the epidermis when pinching the skin on the back of the hand due to differences in density between the epidermis and dermis layers.

The team used double photolithography technology to create wrinkle pixels of various spacings and heights on a single film. The wrinkles had spacings of 800 to 2400 nanometers (nm, 10-9m) and heights of 100 to 450 nanometers, which was confirmed to produce colors across the entire visible light spectrum.

They also succeeded in patterning Dancheong designs based on the wrinkle pixels. The Dancheong patterns appeared only when the transparent film was bent and disappeared when the film returned to its original state.

Overview of Bending-Based Concealable Recognition Variable Structural Color Film Technology.

Professor Kim Taesung explained, "This is a technology that can create variable structural colors through a simple process. Unlike conventional technologies that use dyes, the color does not fade over time, so it will be competitive not only in anti-counterfeiting but also in fields such as stimulus-responsive smart displays."

This technology is planned to be commercialized through technology transfer to Nbst, a domestic company specializing in anti-counterfeiting solutions.

This research was conducted with UNIST's Kaliannan Thiyagarajan and Ji Sungjun as co-first authors, and was published online in the international journal Advanced Functional Materials on January 29 ahead of its official publication.

From the research team (left), Seongjun Ji researcher (first author), Kalyanan Thiyagarajan PhD (first author), Hwisu Jeon researcher. Provided by UNIST

The research was supported by the Institute for Information & Communications Technology Planning & Evaluation and the National Research Foundation of Korea.

This content was produced with the assistance of AI translation services.