The Interaction between Copper and Sodium Dodecyl Sulphate Solutions in the Presence of Air

Abstract

The interaction of oxide-covered copper powder with solutions of sodium dodecyl sulphate has been studied as a function of pH. In acid solutions copper ions dissolve from the oxide layer, the pH rises, and dodecyl sulphate is precipitated, probably as the basic cupric salt. If the final pH is greater than about 4, adsorption of dodecyl sulphate also occurs. There is a range of pH (6-8.5 under the conditions used) where precipitation is negligible or does not occur, but where adsorption is strong. Above this range, adsorption becomes weaker, and at high pH there is little or no reaction. The pH limits for these phenomena will vary with the dodecyl sulphate concentrations and with other conditions. The results are analysed in terms of the interfacial and solution equilibria in the system.