Adsorption of single and mixed surfactants consisting of cocoamidopropyl betaine (CAPB) and sodium dodecyl benzene sulfonate (SDBS) onto zinc surface

Aqueous solutions of surfactants exhibit remarkable differences in their adsorption properties on metal surfaces. This study evaluates the adsorption of surfactant mixtures on zinc metal surfaces. The adsorption of single surfactants cocamidopropyl betaine (CAPB) and sodium dodecyl benzenesulfonate (SDBS) and their mixtures from aqueous solution at mole fractions of 0.00, 0.25, 0.50, 0.75 and 1.00 on zinc powder at 25 °C was studied. The surface tension of the single and CAPB/SDBS surfactant mixtures was measured in the presence and absence of 2 % zinc powder to determine the adsorption isotherms. The depletion method was employed to carry out the adsorption investigation. The amount of the surfactant adsorbed was also calculated from the shaded area between the surface tension versus concentration curves of these surfactants in the presence and absence of 2 % zinc powder. The highest adsorbed amounts were found to increase with the SDBS content. Furthermore, scanning electron microscope (SEM) images of zinc sheets in solutions containing single or mixed CAPB/SDBS surfactants were taken in the presence and absence of 0.05 M HCl. The micrographs indicated that the CAPB-SDBS surfactant layers formed by precipitation can protect zinc metal from acid corrosion.