THE ENERGETICS OF MICELLAR SOLUBILIZATION, AN ACTION OF THE DETERGENCY MECHANISM.
ARMY COATING AND CHEMICAL LAB ABERDEEN PROVING GROUND MD
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Micellar solubilization, an action of the detergency mechanism, is considered from the standpoint of quasi-thermodynamics. The basis of the approach was suggested by the similarity of micellar solubilization and Freundlich adsorption isotherms. Free energy change DG, heat of solubilization DH, and change in entropy DS for the micellar solubilization of Orange OT are calculated using two-phase theory and the Gibbs-Helmholtz equation. It is postulated that the dye concentration in the solution monomer phase is that at the critical micelle concentration. The dye concentration in the solubilized phase is computed for the dye-penetrated portion of the micellar volume. Calculated values of DG in anionic and nonionic surfactants are of the order of magnitude of a physical adsorption. The positive DH values indicate the process is not an adsorption. The positive DS values point to increased randomness or possibly to decreased energy effects due to iceberg water molecule structure surrounding the hydrophobic dye molecules. The loss of the water structure around the latter in the solubilization process would result in their acquiring increased configurational entropy. Author