General surfactant aqueous equilibrium phase behavior

Figure I. General Surfactant Aqueous Equilibrium Phase Behavior...

Structured Surfactant Formulations take advantage of basic aqueous surfiictant phase behavior. Figure 1 shows a schematic of general surfiictant aqueous equilibrium phase behavior as a function of sur ctant concentration. 

Microemulsions are ternary systems containing oil, water, and surfactant. The terms oil and water in a microemulsion system normally refer to oil phase (oil and oil soluble components such as cyclosporine) and aqueous phase (water and water soluble components such as sodium chloride), respectively. The phase behavior of water-oil-surfactant mixtures was extensively studied by Winsor (1948). Based on his experimental observations, Winsor classified equilibrium mixtures of water-oil-surfactant into four systems (1) type I (Winsor I) system where water continuous or oil-in-water (0/W) type microemulsion coexists with the oil phase. In these systems, the aqueous phase is surfactant-rich (2) type II (Winsor II) system where oil continuous or water-in-oil (W/0) type microemulsion coexists with the aqueous phase. In these systems, the oil phase is surfactant-rich (3) type III (Winsor III) system where bicontinuous type microemulsion (also referred to as surfactant-rich middle-phase) coexists with excess oil at the top and excess water at the bottom and (4) type IV (Winsor IV) system where only a single-phase (microemulsion) exists. The surfactant concentration in type IV microemulsion is generally greater than 30 wt%. Type IV microemulsion could be water continuous, bicontinuous, or oil continuous depending on the chemical composition. The phase behavior of microemulsions is often described as a fish diagram shown in Figure lO.I (Komesvarakul et al. 2006). 

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