Phase Behavior of Ternary Systems H₂O — Oil — Amphiphile as Determined by the Interplay of the Oil — Amphiphile Gap and the H₂O — Amphiphile Loop

Abstract

When studying multicomponent mixtures of the type H₂O — oil — nonionic amphiphile one should distinguish between their macroscopic equilibrium behavior and their microstructure. The detailed knowledge of their macroscopic properties, i.e. of their phase behavior as function of temperature (and pressure, if necessary), is a prerequisite for performing meaningful experiments in order to clarify their microstructure. The situation may be compared with that of sailing a ship across the unknown waters. It may then happen that one observes a high surf in some limited area which may incline one to develop some exotic theory about the origin of that surf, whereas a detailed map may reveal the surf to be caused by a reef below the ocean surface. A similar situation may occur when performing, e.g., scattering experiments in homogeneous multicomponent liquid solutions without knowing the location of the critical lines and their end points. It is for this reason that we have emphasized the importance of studies of the phase behavior of such systems. In a recently published review article[1] we have shown that the phase behavior of ternary and quaternary systems with either a lyotropic salt (NaCl) or a ionic amphiphile (SDS) as fourth component can be readily understood on the basis of the theory of phase diagrams as developed at the beginning of this century without assuming any particular microstructure of the solutions.