MECHANISM OF SULFONATE ADSORPTION AT THE SILVER IODIDE-SOLUTION INTERFACE.

In the reported investigation, the effect of n-alkyl sulfonates on the electrophoretic and wetting behavior of silver iodide has been studied. The results show that in the region of negative charge, all the surfactants cease to be surface active at the same pAg, in the neighborhood of pAg 7. This fact has been used to postulate a chemical contribution of the polar head to the total specific free energy of adsorption. It is demonstrated by means of the Stern-Grahame theory of specific adsorption at the double layer that the sulfonates adsorb at lower coverages with their chains horizontally oriented to the Ag1 surface. The free energy change associated with this specific chain-solid interaction is found to be 0. 5 RT per mole of CH//2 group. At higher adsorption densities, and especially for longer chain lengths, association contributes to the adsorption process.