Abstract
Introduction Stratification is the occurrence of layer-like structures. In concentrated surfactant solutions it is a familiar phenomenon. The smectic liquid crystalline phase is a characteristic example. It is less known that under the proper conditions stratification occurs also in free surfactant films. Long ago this has been established by Johonnott (1) and Perrin (2) for aqueous films in air, drawn from concentrated Na-oleate solutions. Later, Bruil and Lyklema (3) observed the same for free aqueous films from concentrated solutions of Na- or Li-dodecylsulphate (NaDS or LiDS respectively). They inferred the occurrence of stratification from some peculiarities in the drainage behavior. The normal drainage behavior, as observed from the intensity of reflected monochromatic light, is a continuous thinning till the first or common black film is formed, in some causes followed by a step-wise formation of the second black or Newton film. The thickness of the common black is sensitive to
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