Hydroxide and hydronium ion adsorption — A survey

The propensity of hydroxide and hydronium ions to accumulate at interfaces is the subject of ongoing scientific debate. Electrokinetic and surface force measurements suggest elevated interfacial concentrations of hydroxide ions across a wide range of pHs. Contrary to this, however, surface-sensitive spectroscopic techniques and molecular dynamic (MD) simulations indicate that hydronium ions have strong surface affinity under similar conditions. Here we review results obtained for gas/water, oil/water and solid/water interfaces. Emphasis is placed on ion adsorption phenomena occurring on polymer films of different hydrophobicity and structure. The results clearly show that asymmetric water ion adsorption is independent of the hydrophobicity of the solid surface. Recently obtained data reveal significant effects of the hydroxide and hydronium ions even on the charging of hydrophobic polymers in the presence of multivalent electrolytes and on the charging of zwitterionic lipid membranes.