Goethite thin-films were prepared by drop-casting 40 μL of a goethite suspension (1.68 g L -1 ) onto microscope glass slides, as detailed in previous work. This drop-casting method results in thin and evenly-distributed goethite films (Figure Detailed peak assignments are shown in Table . The evolution of IR bands indicates more PS was retained at the goethite than at the diamond surface upon adsorption and desorption (Figures and). Differences in the extent of retention result from the variety of ionic, polar and non-polar groups of PS and from the chemistry of the surfaces. For instance, carboxylate groups (1593 cm -1 ) predominate at the early stage of PS adsorption on goethite (Figure , top panel) due to preferential interaction of this anionic group with the positively charged surface of goethite (pHzpc = 8.2). Conversely, methyl ester (1747 cm -1 ) and amide (1655 cm -1 ) groups seem to initiate adsorption of PS at the diamond surface (Figure , bottom panel). Furthermore, in-situ ATR-FTIR spectroscopic results (Figure ) reveal the presence of two distinct surface complexes, namely, a solvent-separated ion pair (SIP, ≡FeO(H) + ⸱⸱⸱(OH2)⸱⸱⸱(O=C)-PS) through the carbonyl of methyl ester (ν(C=O)e at 1749 cm - 1 ) and amide (νs(C=O)a at 1651 cm -1 ) groups, and a contact ion pair (CIP, ≡FeO(H) + ⸱⸱⸱ -O(O=C)-PS) through the carboxylate group (νas(C=O)c at 1592 cm -1 ). Both complexes are classified as outer-sphere complexes (SIP = water-bridge H-bonds and CIP = electrostatic interactions). Insitu time-resolved spectra also show that CIP complexes are slowly desorbed (less reversible)