The mole fractions of TX100 (Xs1) and C16PC (Xs2) at the interface vs. the total surfactant concentrations in the pre-micellar region, C12, at various bulk mole fractions (y1): (●) 0.1093, (□) 0.1995, (▲) 0.2901, (+) 0.3777 (*) 0.5001 and (○) 0.5972.