Dissipative Structures in Liquid Crystals

1. Liquid Crystal A liquid crystal (LC) consists of rod-shaped organic molecules which align in one direction like pencils packed in a box. Therefore, the physical properties measured parallel to the molecular orientation are different from those measured perpendicular. This character called anisotropy is originally known as that of solid crystals. Because center of mass positions of the molecules, however, are randomly distributed like conventional liquids, it has fluidity. Due to these characteristics, LCs simultaneously show both properties of liquids and crystals. LCs have been now-a-day used for various applications in modern technology, e.g. electronic displays called liquid crystal displays (LCDs) for TV and a mobile phone. The orientation of LC molecules can be easily changed by application of electric fields due to the anisotropy and softness like liquids. Owing to the orientation change, polarization of incident light through a LC cell can be changed due to its optical anisotropy, i.e. electrically induced birefringence or electro-optical effect. By application of these properties LCD has been successfully developed. Originally invented LCD nearly half century ago, however, used a different phenomenon in LC as follows. By applying alternating electric fields to LC with negative dielectric constant, flow occurs accompanied with dragging of impurity ions, such as called the electrohydrodynamic effect. Even developed turbulence can occur for high electric fields. Turbulence causes a strong scattering of light, because the orientation of LC becomes random owing to the turbulence. G. H. Heilmeier invented the world’s first LCD using this effect and named its phenomenon “dynamic scattering mode” (DSM) (Heilmeier, 1968). However, this type of LCD could not be commercialized because of slow time response and high electronic power-consumption.