Structure of mixed brushes made of arm-grafted polymer stars and linear chains

The structure of a mixed brush made of arm-grafted polymer stars and grafted linear chains is investigated using the Scheutjens–Fleer self-consistent field method. It is shown that the mixing of stars and chains is thermodynamically favorable with respect to their lateral segregation in the brush. On the other hand, a segregation of linear and starlike macromolecules in the direction perpendicular to the grafting surface is observed. Conformations of stars and linear chains in the brush are determined by the overall molecular weight and the longest path length of linear and starlike macromolecules. Short linear chains occupy the space adjacent to the grafting surface and push the stars toward the brush periphery. In the case of long chains the interior of the brush is filled by the stars while the chains pass through the layer of the stars and expose their ends at the brush periphery. The most interesting is the intermediate situation where the linear chains have larger longest path but lower molecular weight than the stars. In this case, conformations of stars and linear chains depend essentially on the brush composition. When the amount of linear chains is small, they behave as effectively long, but larger fractions behave as short ones. The transition between two regimes is characterized by a bimodal distribution of linear chains and large fluctuation in the position of their free ends