Effect of Bimodal Molecular Weight Distribution on the Polymer Brush

A numerical self-consistent-field model is used to calculate the equilibrium properties of an end-grafted polymer “brush” with a bimodal molecular weight distribution immersed in a good solvent. We find that the longer chains stretch significantly more than the shorter chains in the region near the interface, irrespective of the molecular weight difference or composition. As a result, vertical segregation between the segments of the shorter and longer chains occurs. In systems where the difference in molecular weight between the two chains is small, the longer chain ends are localized at the brush edge. Segment density profiles of two symmetrical brushes compressed together show that stratification persists under compression. The effect of finite molecular weight on the bimodal brush structure is similar to that in monodisperse systems. However, there is also an unpredicted, strong dependency of various aspects of chain configuration on the molecular weight ratio and composition of the bimodal brush.