APPLICATION OF A 2-STATE ADSORPTION-ISOTHERM TO THE ELECTROSORPTION OF DODECYLDIPHENYLPHOSPHINE OXIDE ON MERCURY

The adequacy of a molecular model to describe the adsorption of dodecy ldiphenylphosphine oxide (DDPO) at a mercury electrode has been checke d; the model explicitly treats the electrostatic and nonelectrostatic interactions in the adsorption layer on a molecular level and is based on a two-state adsorption isotherm derived by Sangaranarayanan and Ra ngarajan. Estimates of the adsorption parameters have been obtained on the basis of a method applying nonlinear regression analysis and an e xperimental sample for the decrease in the interfacial free energy wit h the addition of surfactant, as a function of electrode charge densit y and surfactant concentration. A critical discussion of the obtained parameters has been made. Finally an important restriction which shoul d be imposed on adsorption parameters when applying the model has been elucidated and the peculiarities of the model have been shown if this restriction is not fulfilled.