Bimodal polymer brush tethered to a solid/liquid interface

The structure of a dense polymer brush with bimodal molecular weight distribution in good solvent is described. The bimodal brush can be divided into two layers. The layer that is adjacent to the surface contains segments from both constituent chains. The second layer contains only the 'dangling' ends of the higher molecular weight chains. The free energy of the brush is calculated using a Flory type approach. We find that at equilibrium the higher molecular weight chains are stretched in the layer near the surface compared to the shorter chains. This stretching decreases the concentration, thereby reducing segment-segment interaction energy, at the cost of a stretching penalty for the higher molecular weight chains. The degree of stretching is a function of the ratio of surface densities only.