Effects of the potential and the electrolyte nature in the integrity of the O-(2-Mercaptoethyl)-O′-methyl-hexa(ethylene glycol) self-assembled monolayer by electrochemical impedance spectroscopy

Abstract

This work addresses an in-deep study of the ionic conductive properties of the O-(2-Mercaptoethyl)-O’-methyl-hexa(ethylene glycol)-self assembled monolayer (EG7-SAM) by electrochemical impedance spectroscopy in a range of experimental conditions including different aqueous electrolytes and wide potential intervals. The measurements are made in the absence of electroactive probes to get information about the ionic ingress or dynamics into the film. The SAMs stability potential regions comprised between both the potentials for reductive and oxidative desorption processes are here limited and re-defined as regions where ionic ingress occur and these where the ionic permeability does not take place. This distinction leads to a much smaller region where the SAM behaves as an ideal capacitor. Moreover, these features are dependent on the solution pH and electrolyte in contact with the SAM. The temperature effects on the ionic conductivity are also addressed resulting in differences in behavior of complementary parameters. Capacitance spectroscopy analysis of the EG7-SAM helps in the characterization of these films. Thus, information about processes occurring in different time scales (or frequencies) is obtained through the proposed analysis. Putting all the results together, a new perspective of the SAMs conductive properties can be obtained that will be very useful in the choice of a determined layer for specific applications.