Factors Affecting Water Solubilization in Reverse Micelles

FACTORS AFFECTING WATER SOLUBILIZATION IN REVERSE MICELLES 

In Section 3.3 we have briefly indicated that there are various factors that can affect water solubilization in reverse micelles. The importance of the oil-water interface in the context of water solubilization cannot just be overemphasized, and the entity that first comes to the forefront is the surfactant film that separates the two immiscible phases. At the very beginning, therefore, some basic and relevant points on the surfactant film are described below in brief [113, 114, 124, 125, 3]. The interfacial surfactant film can be described as a two-dimensional system in which one can consider a pressure term n [113] this term, characteristic of the film, defines the difference in the oil/water interfacial tension before and after addition of the surfactant to form an interfacial film  

The reduced interfacial tension on continued addition of suitable surfactants/ co-surfactants [114] has been argued to be very low, if not zero. When the value reaches around 10 dyn/cm, the surface energy can get compensated by dispersion entropy this reduces the free energy of the system to a minimum [113]. At very low interfacial tensions, two parameters are considered important  

The transition of W/O microemulsions to the O/W type and vice versa through a bicontinuous form has been discussed in Section 3.2. An additional point worth mentioning here is that a continuous structural inversion W/O - O/W should follow when the natural curvature becomes close to zero (a balanced state [125]). 

A schematic diagram presenting the comparative effects of spontaneous curvature and elasticity of the interfacial film in W/O microemulsions is shown in Fig. 3.8. In a W/O microemulsion, therefore, a maximum water solubilization can be achieved when the interfacial bending stress of rigid interfaces, as also the attractive interdroplet interaction of fluid interfaces is minimized, keeping the interfacial curvature and elasticity at an optimum level. 

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