The secret to improving liquid crystal's mechanical performance (Vol. 48, No. 5-6)

3D plot of the concentration of nanoparticles around a moving edge dislocation in a smectic A liquid crystal

Better lubricating properties of lamellar liquid crystals could stem from changing the mobility of their structural dislocations by adding nanoparticles

By deliberately interrupting the order of materials—by introducing different atoms in metal or nanoparticles in liquid crystals—we can induce new qualities. For example, metallic alloys like duralumin, which is composed of 95% of aluminium and 5% copper, are usually harder than the pure metals. This is due to an elastic interaction between the defects of the crystal, called dislocations, and the solute atoms, which form what are referred to as Cottrell clouds around them. In such clouds, the concentration of solute atoms is higher than the mean concentration in the material. In a paper published recently, the authors have now theoretically calculated the static and dynamical properties of the Cottrell clouds, which form around edge dislocations in lamellar liquid crystals of the smectic A variety decorated with nanoparticles. In this study, they demonstrate a formula previously used to approximate the mobility of dislocations in the presence of Cottrell clouds. They then perform a numerical simulation of the problem to study how the Cottrell cloud erodes when the dislocation moves at high speed. This work could be important, for example, in the context of improving the lubricating performance of such liquid crystals.

P. Oswald and L. Lejček, Drag of a Cottrell atmosphere by an edge dislocation in a smectic-A liquid crystal, Eur. Phys. J. E 40, 84 (2017)