Surfactant dual solubility

Khomane et al. prepared dodecanethiol-capped CdS QDs of 4 nm size by using a Winsor II microemulsion system [242], which are soluble in solvents such as n-heptane, toluene, n-hexane, thus demonstrating the dual role of the anionic surfactant, viz., forming the microemulsion and facilitating the extraction of oppositely charged ions from the aqueous to the organic phase. 

Enhancement of the aqueous solubility by surfactants occurs as a result of the dual nature of the surfactant molecule. The term surfactant is derived from the concept of a surface-active agent. Surfactants typically contain discrete hydrophobic and hydrophilic regions, which allow them to orient at polar-nonpolar interfaces, such as water/air interfaces. Once the interface is saturated, th surfactants self-associate to form micelles and other aggregates, whereby their hydrophobic region are minimized and shielded from aqueous contact by their hydrophilic regions. This creates a discrete hydrophobic environment suitable forsolubilization of many hydrophobic compounds (Attwood and Florence, 1983 Li et al., 1999 Zhao et al., 1999). 

Surfactants are amphiphilic agents that show dual behavior i.e. they are both water and oil soluble. A typical structure of an anionic surfactant is shown in Figure 1 with a water-soluble head and an NAPL-soluble tail. Surfactants are also characterized by their ability to exist in the form of aggregates or micelles above a certain concentration called the critical micelle concentration. The amphiphilic nature also induces surfactants to aggregate at the water-NAPL interface, which brings about a decrease in the interfacial tension. Surfactant micelles also have the ability to solubilize significant volumes of NAPL components such as trichloroethylene (TCE), tetrachloroethylene (PCE), and 1,2-dichloroethane (DCA) among many others. 

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