Society

Korean and British joint researchers explain defects in liquid crystals using topology

A research team led by Professor Jung Joon-woo at UNIST discovered a new defect structure in liquid crystals (chiral liquid crystals) and succeeded in interpreting this defect structure using topology. The topological theory used in conventional liquid crystal research could not explain the topological defect of the found liquid crystal. This study was conducted in collaboration with Durham University and the University of Bristol in the UK. Topological mathematics is a field that studies properties that are preserved or discontinuously changed when the geometric shape of a material changes. It is used in various fields such as space physics and artificial intelligence because it expresses the form of matter with mathematical data.

The research team was able to explain the topological form of the defect by presenting a new ‘chiral phase invariant value’. It was also found that such a topological defect occurs due to the special elasticity of the experimental chiral liquid crystal.

The chiral chromonic liquid crystal used in the experiment has the characteristic that liquid crystal molecules are twisted and arranged like spiral steps when entering a very thin cylindrical tube. It has a left or right twist direction (chirality), where structures with twists in each direction coexist with the same probability in one cylinder. When a chiral material is added in this state, the direction of twisting of the liquid crystal is unified according to the direction of twisting of the added chiral material.

The research team found that the addition of more chiral substances in this state resulted in an unexpected form of topological defect in the liquid crystal. It was a defect caused by the meeting of two structures with the same twisted direction but different rotation angles of 90 degrees and 270 degrees. The topological theory used in liquid crystal research in the past could not distinguish between a 90-degree rotation structure and a 270-degree rotation structure, so despite the experimental observation of defects, it could not be expressed in the language of topological mathematics.

The discovery is expected to help enhance understanding of various chiral substances in medicine and biology as well as liquid crystal research.

Source: https://www.pnas.org/content/118/33/e2102926118

Image source: https://www.sciencedirect.com/topics/materials-science/chirality

*Chirality refers to structural characteristics that do not overlap with one’s mirror image, and is an important research topic in various fields such as physics, chemistry, and biology. A typical example of a chiral structure is DNA containing genetic information. Most DNA with a double helical structure has a right-handed twist, and it seems to be the same as the mirror image, the left-handed double spiral, but it is different. In other words, the chemical composition is the same, but the two do not overlap.

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