The microscopy of the liquid crystalline neat and middle phases of soaps and synthetic detergents

Summary The mesomorphic or “liquid crystalline” neat and middle phases encountered in aqueous systems of soaps and synthetic detergents differ considerably in plasticity. Nevertheless, in fundamental phase studies or the examination of commercial products and processes, identification of these two phases has hitherto been uncertain, particularly when they are mixed with each other or with other phases; even under the polarizing microscope, their identification has not been positive since, by the classical criteria for identifying mesomorphic phases, both are “smectic.” The present work reveals additional criteria by which the two phases may be satisfactorily distinguished. In the first place, there are non‐geometric textures exhibited by middle but not by neat. Conversely, there are planar textures exhibited by neat but not by middle. Furthermore there are important systematic differences even among the focal conic textures upon which the smectic nature of the two phases has previously been predicated. While the microscopic method now makes possible the identification of phase mixtures, it serves also as a rapid method even where one‐phase compositions are concerned. This study is primarily descriptive in its present state of development, but the existence of systematic microscopic differences between these two nominally smectic phases, coupled with their well‐known and pronounced difference in consistency, suggests a fundamental structural distinction between them. Much of the present subject‐matter applies also to such materials as certain wetting agents and dyes, as well as phosphatides and certain other biological substances.