Based on our previous work on single surfactants, we study mixed adsorption of nonionic surfactants consisting of an amphiphilic block-copolymer chain of Lennard-Jones solvophobic and solvophilic interaction centers, designated as H4Tm in a monotonic LJ solvent. Single-surfactant adsorption follows the Langmuir isotherm. Larger tail lengths lead to larger maximum coverages because the surfactant penetrates further into the vapor allowing closer packing. Increasingly attractive tail-tail interactions produce the same effect, again because the surfactant penetrates further into the vapor. Even small attractive tail interactions lead to drastically lower critical aggregation concentrations.

Binary mixtures of H4Tm surfactants display adsorption and tension isotherms intermediate between those of the two single surfactants. Langmuir-based mixture theories do not obey thermodynamic consistency for unequal size species. We successfully apply ideal adsorbed solution theory for all mixtures studied with and without lateral tail interaction. LJ surfactants prove very useful for understanding real surfactant behavior without excessive computation time.