Evidence for the Existence of More Than One Type of Nematic Phase

It is suggested that there may be three types of nematic phases: the skewed cybotactic phase, in which the molecules are arranged in groups in such a way that the centers of the molecules in each group lie in a plane making an angle α (significantly different from 90°) with the mean direction of the molecules in that group; the normal cybotactic phase, similar to the skewed one but with α close to 90°; and the classical nematic phase, in which no regular arrangement between neighboring molecules exists. Three means of distinguishing between these phase types are discussed: the X-ray diffraction pattern, the type of the preceding smectic phase, and the microscopic textures. It is shown that the application of the last two methods to literature data yields support for the concept of different types of nematic phases.