Monte Carlo simulation for the adsorption of diblock copolymers. I. In nonselective solvent

Extensive Monte Carlo simulations have been performed to study the adsorpti on of diblock copolymers from a nonselective solvent on an impenetrable sur face. The efforts were concentrated on depicting the microstructure of adso rption layers. In simulations, diblock copolymer molecules are modeled as s elf-avoiding linear chains composed of r(A) segments of A and r(B) segments of B, where the former is attractive to the surface while the latter is no nattractive. The adsorption information including segment density profiles, adsorption amount and isotherms, adsorption layer thickness, bound fractio n and surface coverage were obtained by detailed analyses on comprehensive simulation data under various conditions. The microstructure of adsorption layers, primarily the profiles of the adsorbed segments corresponding to ta ils, loops, and trains, and the size distributions of these adsorption conf igurations are presented. As a whole, the adsorption layer thickness is mai nly determined by the length of the nonattractive block. The effect of the adsorption energy and the chain composition f, the latter is the proportion of attractive segments A in a diblock copolymer chain, on various adsorpti on properties has been inspected. Comparisons between results of this work and those of previous simulations as well as corresponding experiments were made and many useful conclusions have been drawn. It is shown that the ads orption amount increases monotonically with the increase of f when the adso rption energy is relatively small. However, if the adsorption energy has a larger value, the adsorption amount exhibits a maximum at certain value of f dependent on the length of the block A and the magnitude of the adsorptio n energy. This trend coincides well with the experimental results of Tiberg [Langmuir 10, 2294 (1994)] and Evers 's SCF calculations [J. Chem. Soc., F araday Trans. 86, 1333 (1990)]. Why some previous work failed to simulate t his phenomenon is also explained. (C) 2001 American Institute of Physics.