Influence of Charge Sequence on the Adsorption of Polydispersed and Monodispersed Polyelectrolytes onto Monodispersed Polyelectrolyte Brush

We use coarse-grained molecular dynamics to elucidate the role of charge sequence on the adsorption efficacy of oppositely charged free monodispersed and polydispersed polyelectrolytes on to a polyelectrolyte brush. We consider four different model systems wherein the free and the brush polyelectrolytes can have either brush or alternating charge sequence. Our model treats the polyelectrolytes in a bath of implicit solvent, excess salt and explicit counterions. For monodisperse systems, the adsorption efficiency is highest when both the free and the brush polyelectrolytes possess a block charge sequence, and it is lowest when both the free and the brush polyelectrolytes possess an alternating charge sequence. By computing the free energy, internal energy and entropy of adsorption using umbrella sampling methods, we find that the origin of the differences in adsorption efficiency for different charge sequences in monodispersed systems is enthalpic. Additionally, equilibrium conformations for different charge sequences reinforce the results obtained from energetic calculations. We also show the changes in adsorption efficacy as a result of polydispersity in the free polyelectrolytes.