Liquid Crystals

THERE are substances which are liquid in their mobility and crystalline in their optical behaviour. The latter property suggests that there must be some degree of arrangement of the component molecules, and the former that this arrangement is readily disturbed though it may be as readily renewed. Such substances are generally attacked the general problem from various sides, Vorlander, Schenck, Friedel, Grandjean, Mauguin, Oseen and others. Quite a large literature has grown up round the subject. Friedel has given a full account of his experiments in the Annales de Physique. The present state of knowledge may be inferred from the account of the general dis-FlG. 1.Enlarged photomicrograph of a liquid crystal. A Nicol prism is used as analyser; there is no polariser. The substance is ethyl pam-azoxybenzoate, temperature 114 °-120 ° C. Notice the polygons and the appearances of cones within them. The white circles are air-bubbles: the grey portions are liquid. The diameter of the original before magnification is 0-076 cm.described as ‘liquid crystals’. It is argued, especially by Friedel, to whom we owe so much of our knowledge of their properties, that the title is bad, because the substances are neither perfect crystals nor perfect liquids. Friedel would call them mesomorphs, which is much more logical, since the conditions to be described are intermediate between other conditions that are well known. The term ‘liquid crystals’ is, however, simple and suggestive, and those who use it are not likely to be misled.