Development of Essential E-Ink Material
Discovering van der Waals Colloidal Crystals
Results from Professor Lee Seung-woo’s group published online in Advanced Materials

▲ (From left) Cho Yong-deok (postdoc researcher, first author), Park Sung-hun (student in integrated master-doctoral degree programs, co-first author), and Kwon Min (master student, coauthor), 

Kim Hyeon-ho (student in integrated master-doctoral degree programs, coauthor, Professor Huh Ji-hyeok (Hanyang University, coauthor), and Professor Lee Seung-woo (corresponding author).

Professor Lee Seung-woo’s group of the KU-KIST Graduate School of Converging Science and Technology developed a method for assembling colloidal crystals of a novel form using van der Waals force.

Their results were published online on March 7 in Advanced Materials (IF: 29.4), a globally renowned journal.

* Title of article: Van der Waals Colloidal Crystals

* URL: https://onlinelibrary.wiley.com/doi/10.1002/adma.202312748

Colloidal crystals have been used as an essential material for E-ink. The newly developed van der Waals colloidal crystals feature the world’s highest reflectivity in the visible light region, and so the results are highly significant for the innovation of E-ink.

Professor Lee’s group successfully developed silica colloids including gold particles, optimized the van der Waals forces, and prepared the colloidal crystals in a fluid state. The results of the study showed that photonic crystals may be maintained through van der Waals forces in a liquid state, suggesting a new methodology for colloidal assembly.

The newly developed colloidal crystals can exhibit various colors based on the specific photonic bandgaps in the region of the visual light. The colloids developed by the group exhibit high efficiency and purity, and this is attributed to the perfect colloidal crystal structure and the gold particles.

The technology developed by the research group allows for the manufacture of displays of larger area than when using photonic crystals based on the conventional colloids, thereby providing a significant economic advantage. The colloids developed by the technology are an essential material for recently emerging fields such as E-ink. The high performance and resolution and the low power consumption supported by this new technology compared to existing E-ink materials suggest that the major limitations of E-ink technology may be overcome. Since the newly developed colloidal crystals allow for the implementation of various colors based on the photonic bandgaps, E-ink display color ranges can be extended, and their resolution improved.

One important feature of the technology is its excellent visibility. The van der Waals crystals can maintain excellent brightness and visibility even under strong sunlight, meaning that they can be applied to varied outdoor applications including outdoor signboards, traffic lights, and information displays. In addition, thanks to their enhanced color saturation, the colloidal crystals developed by the group are also capable of expressing clear and accurate colors even in outdoor spaces, thereby improving the color accuracy and quality of outdoor displays.

<Figure 1>

Image description: An image of silica photonic crystal assembly including gold particles through van der Waals forces.

(Left) An image of colloidal crystals in a fluid state observed through a photonic microscope. (Right) A scanning electron microscope (SEM) image of silica colloids including gold particles. Photonic crystal assembly was performed in a fluid state using van der Waals forces, successfully producing photonic crystals in a fluid.

<Figure 2>

Image description: An outdoor view of the photonic crystals in a fluid.

The silica photonic crystals including gold particles developed in the present study were used to produce a large-area film in the form of a wafer. The reflectivity was excellent during the daytime, indicating that the new basic material may maximize E-ink efficiency.