A research team led by Kim Shin-hyun, Assistant Professor of Chemical and Biomolecular Engineering at KAIST, announced on January 15 that it successfully developed a technology to microcapsulate photonic crystals, which is regarded as a next-gen optical material, by using osmotic pressure. The study was conducted in a partnership with Harvard University.
The refractive index of photonic crystals changes periodically at half of the wavelength of light. In fact, photonic crystals are called semiconductors for light, since they can control light propagation at specific wavelengths, and promise innumerable technological applications. They can be found in nature in the wings of butterflies or the tails of peacocks.
However, it has been difficult to commercialize photonic crystals due to the fact that a change in colors is impossible, in that reflected colors are mostly realized by a fixed structure. The complicated manufacturing process is not helpful, either.
To address the problem, the team improved the manufacturing process by encapsulating liquid crystals to form ink capsules, and fabricating photonic crystals in the form of microcapsules at the 100-nanometer level. In addition, the research team used rubber covers for those capsules in order to freely change their shape.
The research team also applied the principle of osmotic pressure to minute water droplets that contain nanoparticles. With the volume of water droplets decreasing because of osmotic pressure, nanoparticles themselves were arranged in a regular manner, which led to the formation of liquid crystals inside capsule covers. The team was finally able to make microcapsules of photonic crystals with a uniform size by using microfluidics that realized a small passage at the 100-nanometer level.
Professor Kim said, “It is possible to commercialize ink capsules of tiny photonic crystals, which could be used for next-gen reflective-type color displays that can be bended or folded. Those photonic crystal capsules could also be utilized as core optical materials to make body-insertable biosensors."
The research findings were published online in the January 7 issue of Nature Communications, a bi-monthly scientific journal published by the Nature Publishing Group.