Contrary to the conventional textbook picture, not all solids completely lose their order when they melt. Some molecular solids instead form liquid crystals, materials with the molecular orientational order of a solid but the mobility of a fluid. Such liquids have attractive optoelectronic properties: Their molecular ordering makes them birefringent, and because the molecules can be manipulated with electric fields, that birefringence can be modified with the flip of a circuit switch. (See the article by Peter Palffy-Muhoray, Physics Today, September 2007, page 54.)
To create liquid crystals for devices, however, you need to be able to direct their alignment. One of the most popular strategies is also a simple one: Rub two polymer-coated glass plates with a cloth, face them to form a cell, and fill the cell with a liquid crystal of elongated molecules. The rubbing stretches the polymers and imprints the coating with microscale grooves,...
