Studies on adsorption behavior of sulfonate surfactants on a lead electrode in sulfuric acid

The electrochemical behavior of a lead electrode was studied in 5 M sulfuric acid with various sulfonate surfactants, viz. amine perfluoroitlkylsulfonate (FC-99), sodium dodecylbenzenesulfonate (SDBS) and sodium lignosulfonate (SLS), and also in relation to the structural characteristics and the adsorption state of the additives on different surfaces of the electrodes. The results indicate that FC-99 molecules adsorb on the metallic lead surface by their hydrophilic heads whereas they adsorb on lead sulfate by their hydrophobic chains vertically, but the SDBS molecules adsorb on metallic lead and lead sulfate flat or partly flat, with their hydrophilic heads oriented toward the electrode. For SLS, the adsorption state is different from those of the other two surfactants. At lower concentrations (similar to 5 ppm), the SLS molecules adsorb on the metallic lead and lead sulfate with a partly flat orientation by their sulfonate groups, just as SDBS molecules do. At higher concentrations (greater than or equal to 10 ppm), the SLS molecules adsorb on the lead and lead sulfate perpendicularly with their hydrophilic heads oriented toward the bulk solution.