Predictive Modeling of Microemulsion Phase Behaviour and Microstructure Characterisation in the 1-Phase Region

Microemulsions are dispersions of water and oil stabilized by one or mixtures of surfactants. The key differentiators from other dispersions are: (i) domain size of the dispersed phase is of the order of 5-100 nm in size (Schulmann et al., 1959); (ii) thermodynamically stable (Zana, 1994), and (iii) optically isotropic (Danielsson and Lindman, 1981). Commonly observed structures are: oil in water (o/w), water in oil (w/o) and bicontinuous (Scriven, 1976). Microemulsion formation has proven to be an effective approach in enhancing oil solubilisation and reducing oil-water interfacial tension (IFT) in many industrial applications. Examples include enhanced-sub surface remediation (Harwell et al., 1992; Brusseau, 1999) , drug delivery (Djordjevic et al., 2004; Kogan & Garti, 2006; Ghosh et al. , 2006), detergency (Rosen, 2004; Srivastava et al., 2006; Solans & Kuneida, 1996; Tongcumpou et al., 2006) and nano particle synthesis (Sjöblom et al., 1996). Forming an efficient microemulsion system requires an equal balance between surfactant-oil and surfactantwater interactions, which has proven to be a very challenging task for certain types of oils (e.g., vegetable oils and triglycerides) (Miller, 1991; Minana-Perez, 1996). In addition, different applications require specific degrees of solubilisation and IFT reduction. It is no surprise, then, that formulating microemulsions for specific industrial use has been referred as both an art and science (Salager, 2006). This is because microemulsion design requires not only a great understanding of molecular interactions, but also a deep understanding of thermodynamic principles (Bourel & Schechter, 1998).