USE OF HIGH-FREQUENCY AC VOLTAMMETRY TO STUDY KINETICS OF PHYSICAL ADSORPTION AT MERCURY ULTRAMICROELECTRODES

Adsorption kinetics of small organic molecules was studied by ac volta mmetry with mercury ultramicroelectrodes in the frequency range 0.22-6 .25 MHz. It was found that the activation energy of the adsorption pro cess can be expressed as a linear combination of the electrical compon ent of the standard free energy of adsorption (a major contribution) a nd the energy of lateral interactions (a minor contribution). The resu lts suggest that, during the adsorption process, work against an elect rical field must be performed before excess energy (due to the change in the hydrophobic interactions) is released. The final state is reach ed by a rotational and translational motion of the surfactant molecule . At the zero charge potential the rate constant reaches the maximum v alue of (4.6 +/- 0.3) x 10(9) s(-1). This value indicates that the vis cosity of interfacial water at mercury near the zero charge potential is about 1.7 times higher than the bulk viscosity.