Once the adsorption PMF and the area per molecule were determined, the MTT model for surfactant adsorption developed by Nikas et al. was used to construct adsorption isotherms for the OFMs on hematite from PAO4. The model starts with a surface equation of state based on the following assumptions: (1) single monolayer adsorption, (2) the surfactants in the monolayer are modelled as hard-disks of radius r with short-ranged attractive interactions, (3) exclusively non-ionic surfactants are considered, and (4) the headgroups are located on the Gibbs dividing surface (minimum of the PMF) while the tailgroups are pointing towards the liquid phase. From this equation of state, the surface chemical potential,