Non-Equilibrium Steady State Response and Fluctuations of Sheared Nematic Liquid Crystals

Liquid crystals (LCs) are intermediate states between conventional liquids and solid crystals [1]. They have fluidity like liquids and anisotropy like solids at the same time. The molecules tend to point in one direction, which is designated by a unit vector n called the director. Many important physical phenomena of NLCs such as reorientation of director under external fields and flow properties can be studied by regarding a NLC as a continuous medium. The couplings between the director and external fields (electric and magnetic fields, shear) are important for controlling the orientation: for example the coupling with electric fields is widely utilized for liquid crystal displays. The shear flow has a unique property that it easily breaks the time reversal symmetry and brings fluids far from equilibrium [3]. In general, application of steady shear flow can make NESSs. Orihara et al. [4] has applied a steady shear flow to a liquid crystal as a source of non-conservative forces and measured the shear stress response to small ac electric fields applied along the velocity gradient, as shown in Fig. 1. In their experiment, they use 5CB (4-n-pentyl-4'-cyanobyphenyl) with a positive dielectric anisotropy.