STRUCTURE OF GRAFTED POLYMERIC BRUSHES IN SOLVENTS OF VARYING QUALITY - A MOLECULAR-DYNAMICS STUDY

A molecular dynamics simulation of polymeric brushes in solvents of varying quality is presented. The resulting equilibrium structures are compared with those predicted by self-consistent field (SCF) analysis. The scaling of the brush height is found to agree with the SCF predictions at temperatures T > T(theta), where T0 is the theta temperature of the solvent. The agreement at T < T(theta) is poor, probably resulting from the separation of the brush into monomer-rich and monomer-poor phases. This phase separation disappears with increasing grafting density and chain length. Good agreement is found with the SCF predictions for the density profile of the monomers and of the free ends of the chains and for the structure factor under good solvent conditions. The agreement of these properties with the SCF predictions at and below To is not as good. Even the scaling behavior of the profiles with respect to the chain length and the grafting density is found to be inconsistent with the SCF analysis. The effect of a small attractive surface interaction on the structure of the brush is also studied.