Oil Droplet Detachment from Metal Surfaces as Affected by an Applied Potential

Abstract

Removal of organic contaminants from metal surfaces submerged in an aqueous surfactant solution can be improved by application of an applied potential. Earlier work has shown that the detachment of organic droplets is noticeably affected by variations in the pH of the solution and charge of the surfactant. Modifications in solution pH result in modifications of the electrostatic charge of the solid surface, which, depending on the charge and nature of the surfactant, will improve or hinder adsorption of surfactant at the solid–aqueous interface. This adsorption of surfactant molecules is of great importance to the detachment of organic droplets and, consequently, on the determination of cleaning efficacy. It is proposed that modification of the surface charge through application of potential will also result in changes in the adsorption of surfactant and, as a result, will alter drop detachment. Experimental results from a battery of tests for the removal of industrial quench oil from a stainless steel surface with different applied potentials are shown. Additionally, several different surfactants were examined, and drop detachment times and cleaning efficiency by ultrasonication were measured. A mechanistic model describing the affect of potential on surfactant adsorption was proposed, and a correlation between detachment time and cleaning was developed for some of the surfactants.

Acknowledgments

The authors thank Dr. Costas Tsouris at Oak Ridge National Laboratory for his assistance. This work was supported by the Environmental Management Science program, U.S. Department of Energy, through a grant to The University of Tennessee and under contract DE-AC05-00OR2275 with UT-Battelle, LLC.