Liquid crystals that can prevent fake money and documents

The research team has developed the production technology of changing the color of liquid crystals, which can be used instead of ink to protect money, identity cards and other documents from fake.

Photon-crystalline materials are able to show different colors without the presence of pigments, but due to its periodic nanostructure, reflecting the light of certain waves. The presence of such a repeated structure on liquid crystals allows manufacturing a material that manifests simultaneously several optical characteristics. However, to achieve such an effect, it is necessary to consistently increase the set of layers with different patterns, which is a very complex process.

Scientists from the Korean Institute of Science and Technologies have developed a simple method of manufacturing multi-layer liquid crystals thick with human hair. To create them, the team used a hydrophobic liquid crystal material, organic alcohol as a hydrophilic moisturizing agent, as well as a co-solvent dissolved both in oil and in water.

The mixture of three of these substances is emulsifiable in water to form a dropper of the microemulsion. The exchanges between the co-solvent, the moisturizing agent and water molecules through the surface of the emulsion droplets led to the separation of hydrophobic and hydrophilic layers.

Depending on the initial ratio of the mixture components, they are separated by 1-5 layers, which can be freely controlled. In addition, with a continuous separation of phases within each drop of emulsion, the concentration of chiral impurity inside liquid crystals changes, which leads to the appearance of several structural colors. This allows you to use them to combat fakes.

Scientists expect a new technology to add unique optical characteristics of materials. On its basis, the team also plans to further develop various functional particles for composite materials.

Previously, we also reported the development of a crystal that enhances the laser

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