Liquid crystals have been known since Reinitzer and Lehmann discovered that cholesterol melts in two steps, first becoming a cloudy liquid that becomes clear at higher temperature. By the middle of the 20th century it was found that many, mainly organic, molecules form a number of phases that are intermediate between a solid and ordinary isotropic liquid. These molecules fall into two classes. In the first class, now called “nematic” in a broader sense, the positions of the molecules are completely random, like in an ordinary liquid, but the molecules are locally all pointing in one average direction, called the “director.” This process gives rise to strong optical birefringence that, together with the ease of manipulating the director with electric fields, form the basis for the ubiquitous use of modern liquid-crystal displays. The second class of smectic and columnar phases exhibits, in addition to orientational order, partial positional ordering into planes or columns, with the molecules free to move in the planes and columns sliding past each other. Since the early 20th century just three nematic phases have been known. In PNAS, Chen et al. (1) report on experiments that confirm the existence of a fourth nematic phase with some very interesting properties.
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