“…For instance, an increase in the sulfopropyl content tends to increase γ int e , while it lowers γ e . It was shown for low-molecular-weight surfactants that at high surface coverage, the surface excess was lower at the oil-water interface than at the air-water interface [61]. The authors explained this result by the fact that at the oil-water interface, surfactant molecules are in the vicinity of oil molecules and have to share the interface, while at the air-water interface, surfactant molecules are free to assemble.…”