Discovered 130 years ago by Friedrich Reinitzer, liquid crystals are ubiquitous today—in displays small and large, in cosmetics and fashion, in cutting-edge sensors and actuators, and more. (See the article by Peter Palffy-Muhoray, Physics Today, September 2007, page 54.) The rod-, disk-, or even banana-shaped molecules that make up liquid crystals have orientational order but at most only partial positional order. When matter is in a liquid-crystalline state, or mesophase, its refractive index, elastic modulus, viscosity, and other physical properties are strongly anisotropic, and the state is extremely sensitive to external factors such as temperature, electric and magnetic fields, and shear. Liquid crystals continue to attract attention from experimental, theoretical, and practical—not to mention aesthetic—points of view.
This natural-color photo shows a liquid crystal, 2.5 mm across and 5.1 μm thick, viewed through crossed polarizers. It’s in a so-called smectic C* phase: Chiral molecules line up parallel to...
