(Seq. 6) Similar to the equilibrium stage of adsorption, the relative contribution of carboxylate groups to the spectra is proportionally higher at low PS concentrations even after surface rehydration. This suggests that electrostatic interactions between carboxylate and surface hydroxyl groups remain intact. Some solvent-separated ion pairs (SIP complexes) may form due to partial rehydration, though not fully (Figure ). As discussed previously, methyl ester and amide residues contribute to PS self-association via H-bonding. We suggest methyl esters on PS chains do not directly interact with the goethite surface since the surface would prefer to interact with polar or charged groups, pushing hydrophobic components away from the surface. This potentially leads to desorption of hydrophobic PS fragments. We posit lower relative PS desorption from the goethite surface (compared to the diamond surface) results from a less fluid organo-mineral interface inherent to the stronger (electrostatic) interaction between the carboxylate groups of PS and the hydroxylated surface.