In situ electrochemical-ellipsometry studies of charge-transfer processes at the liquid/liquid interface

In situ ellipsometry has been used to characterise the properties of the interface between 1,2-dichloroethane (containing tetrabutylammonium hexafluorophosphate) and water (containing lithium sulfate) during electrochemical potential step (chronoamperometry) experiments with a four-electrode potentiostat. The ellipsometry behaviour was analysed according to changes in the real Delta (r(r)) and imaginary Delta (r(i)) signals measured at the Brewster angle during polarisation of the interface between two immiscible electrolyte solutions (ITIES). It was found that both the Delta (r(r)) and Delta (r(i)) responses represented relatively slow changes through the interface profile that scaled reversibly with the sign and magnitude of the potential jumps. The ellipsometry responses provided spectroscopic evidence of ion-transfer and accumulation processes via measurement of changes in the refractive index and variation of the dielectric constant in the interface region. The spectroscopic data were consistent with previous models that indicate the ITIES is composed of a mixed solvent layer with varying penetration of electrolyte ion pairs.