Both of these surfactants have several polar groups capable of interacting with the oxygen or iron atoms in the surface. They are also large, flexible molecules that can adopt many different possible conformations at the solid-liquid interface. Consequently, two distinct inner-sphere adsorption modes are present for GMS and GMO, as can be seen from the corresponding PMFs. The different situations and adsorption modes depicted in Fig. and 4c are associated to changes in the derivative of the PMF, i.e. changes in the mean force experienced by the colvar at that distance. The barriers between 0.6 nm and the bulk are once again due to the interaction between the tail and the solvent molecules.