Cosolvents and Surfactant Effects

Free metal ion Inoiganic con lexes Organic coD LeKes Colloids large polymere Surface bound Solid bulk phase, lattice 

Cu C11CO3 CuOiF Cu(COj)2. P- FiilvaLe Inorganic Organic Fe—OCu CuO CU2(0I])2C03 Solid sollution 

Many contaminants, such as pesticides and pharmaceuticals, reach the subsurface formulated as mixtures with dispersing agents (snrfactants). Snch formulations increase the aqueous solubility of the active compounds, and these snrfactants form nearly ideal solutions with the aqueous phase. 

Addition of a cosolvent is an alternative mechanism to increase contaminant solubility in an aqueous solution. When a contaminant with low solubility enters an aqueous solution containing a cosolvent (e.g., acetone), the logarithm of its solubility is nearly a linear function of the mole fraction composition of the cosolvent (Hartley and Graham-Bryce 1980). The amount of contaminant that can dissolve in a mixture of two equal amounts of different solvents, within an aqueous phase, is much smaller than the amount that can dissolve solely by the more powerful solvent. In the case of a powerful organic solvent miscible with water, a more nearly linear slope for the log solubility versus solvent composition relationship is obtained if the composition is plotted as volume fraction rather than mole fraction. 

Yalkowsky and Roseman (1981) and Rubino and Yalkowsky (1987) suggest the following equations for relating solubility of a nonpolar solute (SJ in a binary mixture of an organic solvent and water to that in pure water (S )  

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