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Liquid crystals are phases in which the particles tend to point in the same direction. Their behaviour is similar to pieces of chalk, which spontaneously align when they are put in a box, which is vigorously shaken. A special class of liquid crystals are the so-called chiral nematic liquid crystals in which the particles are not only aligned in the same direction but they are also slightly rotated with respect to each other, thereby forming a chiral helical structure. These materials are widely used in applications such as LCD screens, but the microscopic origin of the helical arrangement is still not well understood. Simone Dussi and Marjolein Dijkstra (Physics) show using simulations that the chiral behaviour can be explained solely by the shape of the particles.  This knowledge makes it possible to tune the chiral behaviour in liquid crystals by changing the particle shape. Dussi and Dijkstra describe their results in an article in the 12 April issue of Nature Communications.

By carefully selecting the particle shape, the researchers were able to show by computer simulations that twisted triangular prisms can spontaneously form chiral nematic phases. In this phase, the particles are not only aligned, but they are also slightly rotated with respect to each other, thereby forming a chiral helical arrangement. The length of the helical pitch can be changed by applying an electric field, which is the principle behind LCD screens.

Liquid crystals

Liquid crystals are a kind of matter that possess both liquid-like and crystalline properties. In a liquid, particles move around randomly, while particles in a solid are nicely ordered onto a crystalline lattice. In a liquid crystalline phase, the particles move around randomly, but their orientations are nicely ordered as in a crystal. Liquid crystals are used in ‘liquid crystal display’ screens, which are commonly applied in calculators, digital watches, computer monitors and mobile telephones.

Publication

Entropy-driven formation of chiral nematic phases by computer simulations
Simone Dussi and Marjolein Dijkstra
Nature Communications, 12 April 2016, doi 10.1038/NCOMMS11175