The research team has developed a technology to produce color-changing liquid crystals that can be used instead of ink to protect money, identity cards and other documents from counterfeiting.
Photonic crystalline materials are able to display different colors not due to the presence of pigments, but due to their periodic nanostructure, which reflects light of certain waves. The presence of such a repeating structure on liquid crystals makes it possible to fabricate a material exhibiting several optical characteristics simultaneously. However, to achieve such an effect, it is necessary to sequentially build up many layers with different patterns, which is a very complex process..
Scientists at the Korea Institute of Science and Technology have developed a simple method for making multi-layered liquid crystals as thick as a human hair. To create them, the team used a hydrophobic liquid crystal material, organic alcohol as a hydrophilic moisturizing agent, and a co-solvent that is soluble in both oil and water..
A mixture of these three substances is emulsified in water to form microemulsion droplets. Exchanges between a cosolvent, a wetting agent, and water molecules through the surfaces of emulsion droplets led to the separation of the hydrophobic and hydrophilic layers..
Invented liquid crystals that can prevent counterfeit money and documents
Depending on the initial ratio of the components of the mixture, they are separated for 1-5 layers, which can be controlled freely. In addition, with continuous phase separation inside each emulsion droplet, the concentration of chiral impurities inside liquid crystals changes, which leads to the appearance of several structural colors. This allows them to be used to combat counterfeits..
Scientists expect the new technology to help add unique optical characteristics to materials. Based on it, the team also plans to further develop various functional particles for composite materials..
We also previously reported on the development of a crystal that amplifies the laser 13 times more efficiently. existing analogues.
text: Ilya Bauer, photo: Korea Institute of Science and Technology