EMPIRICAL RELATIONSHIPS BETWEEN THE KRAFFT POINTS AND THE STRUCTURAL UNITS IN SURFACTANTS

Depending on their structure, surfactants display different behaviour when in contact with water. The simplest case is that they dissolve into water and form micelles above a certain critical concentration (CMC). Other categories of surfactants are insoluble in water and swell into a liquid- crystalline phase (the D phase). At high water concentrations there will be a dispersion of the D phase and almost pure water. A third category of surfactants arc insoluble and form crystals when contacted with water. For ionic surfactants there is a temperature, called the Krafft point (KP), below which the solubility is quite low and insufficient for micellization. Above the Krafft temperature, micelle formation evidently becomes possible and there is a rapid increase in the solubility of the surfactant. It has been generally accepted that this behaviour arises from the fact that unassociated surfactant monomer has a limited solubility, whereas the micelles are highly soluble.