Monte Carlo simulation of the adsorption from a nonselective solvent of symmetric triblock copolymers with sticky end blocks

Abstract

The adsorption of symmetric triblock copolymers from a nonselective solvent on an impenetrable surface has been studied by a lattice Monte Carlo simulation method. The triblock copolymers are ANABNBANA with NA=10, 5⩽NB⩽40, and surface interaction parameters −1.5⩽ε⩽−0.5, where A is the adsorbing block and B is the nonadsorbing block. The concentration, expressed as the volume fraction, is varied over the range 0.012⩽c⩽0.143. This report describes the adsorption isotherms and the kinetics of the adsorption in the simulations. At short times, the adsorption is diffusion controlled. Good approximations to the Langmuir adsorption isotherm are observed for the equilibrium adsorbed amount, Γ and surface coverage of the adsorbing block, θA. The results are compared with recent simulations for diblock copolymers. The adsorbed amount is less for the diblock than for the triblock copolymers at low concentration. The surface coverage by the adsorbing block is the same for both cases at weak surface adsorption. The surface density profiles are also obtained and compared. The adsorbed number of chains per unit area (σ) and surface coverage for triblock copolymers under weak adsorption conditions are found, respectively, to scale according to the relationship σ, θA∼1/β2, where β=(NB/NA)3/5, which implies the importance of the nonadsorbing block size for the adsorption features of triblock copolymers. These results confirm the experimental observation reported recently by Dorgan et al. [Macromolecules 26, 5321 (1993)].