Counterion Binding in Adsorbed Surfactant Films Studied by Surface Tensiometry and Total Reflection XAFS Spectroscopy

Abstract

Headgroup–counterion interaction was investigated in terms of counterion hydration for the adsorbed films of dodecyltrimethylammonium salts with various counterions such as DTACl, DTABr, DTABF4, and DTA2SO4. Our experimental data supported that the interaction between TA heads and divalent SO4 ions was controlled by the balance between Coulomb force and steric hydration effect. In contrast, that between TA heads and monovalent ones (Cl–, Br – and BF4–) was well explained by the capability of headgroup-counterion contact pair formation accompanied by partial dehydration.