ABSTRACT
This chapter summarizes the state of knowledge of the phase behavior of oil/water/polyoxyethylene alcohols in relation to the characteristics of the surfactant molecule, of its solutions in oil or in water, and of its multiphase systems. It provides the structural aspects, calling attention to the relation between structures in isotropic phases and the presence of liquid crystalline phases. The partial mutual miscibility of oil and water can be promoted by using a huge number of nonionic compounds: they range from the simple amphiphatic molecules like short alcohols to block copolymers, the very surface active agents. Like ordinary organic compounds, binary mixtures of oil and nonionic surfactants exhibit lower liquid-liquid solubility curves, with an upper consolute critical point. For effective nonionic surface-active agents, that phase exists only for a rather narrow range of the experimental conditions. Apart from the gathering of punctual observations, the number of actual structural determinations in systematic relation to phase behavior of nonionics is still very limited.
