Effects of grafting geometry and solvent quality on the structure of bimodal polymer brushes

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Abstract
We carry out extensive off-lattice computer simulations of bimodal polymer brushes and discuss the effects of different grafting geometry and solvent quality on the structure of such mixed polymer brushes. For a flat grafting surface and good solvents, the short and long chains segregate vertically and the long chains stretch more in the coexisting region. The situation is different for polymers grafted onto a flat surface and in contact with poor solvents where vertical segregation between the long and the short chains is found to be much weaker. Also, as the function of short chains increases in the layer, both the short and the long chains stretch less. This is different from the good solvent case where the stretching of the short chains increases as the short chain fraction increases. For a spherical grafting surface and in good solvents, the stretching of the two type of chains is similar in the inner layer. In a poor solvent, the situation is similar to a flat grafting surface with poor solvents and both types of chains are equally stretched over the entire region of the layer.