Adsorption of perfluorocarboxylic acids at the silica surface†
Abstract
Water molecules may force the hydrophobic perfluoroalkyl chain of perfluorocarboxylic acids (PFCAs) to aggregate at hydrophobic siloxane patches (Si–O–Si) of the silica surface despite electrostatic repulsion between surface silanol (SiO−) and the carboxylate (–COO−) headgroup of PFCA. Acidic pH and background cations promote the adsorption further by reducing the anion–anion Coulomb repulsion.