Adsorption of PS on the diamond crystal (i.e., the hydrophobic surface) was used to form the PShydrophobic surface. Due to the lower surface area of the diamond crystal, a greater concentration of PS was needed to acquire high quality IR spectra ([PS] = 14.1 -196.9 μM). PS adsorption was followed by a desorption experiment where a solution with the same background electrolyte (no PS) was introduced until equilibrium. Experiments were replicated 3-4 times on freshly prepared goethite films or clean diamond crystal surfaces under identical conditions. All in-situ experiments were conducted under ambient atmosphere and using a close flow-through system at a rate of 0.85 mL min -1 (flow velocity = 4.5 × 10 -3 m s -1 ) using a peristaltic pump (Cole-Parmer, IL). All spectra were collected by subtracting the spectrum of the background electrolyte from the spectrum of each sample. Interfacial IR spectra were collected every 2 min (200 scan time) with a spectral resolution of 4 cm -1 from 4500 to 850 cm -1 . After collection, spectra received an atmospheric compensation, a nine-point Savitsky-Golay smoothing and baseline correction to remove instrumental drift. All post-hoc manipulations were performed using OPUS v.7.2 software (Bruker Corp., Billerica, MA).