Strongly charged polyelectrolyte brushes: A molecular dynamics study

We use molecular dynamics simulations to study polyelectrolytes end-grafted to a surface. Our model includes counterions explicitly and treats the ful l long-range Coulomb interaction. Strongly charged polyelectrolytes with no added salt are investigated, where the counterions are localized inside th e brush and electroneutrality is satisfied locally. At this stage, we do no t rule out that finite system size influences the prefactors of our scaling results. Irrespective of this question we find that the brushes are collap sed with a thickness linearly proportional to the chain length and the graf ting density. The counterion distribution is strongly inhomogeneous, and co unterion condensation can be observed although the Bjerrum length is smalle r than the average bond length. The osmotic counterion pressure is much lar ger than the ideal gas value. Counterion diffusion is anisotropic and is en hanced at higher grafting densities. We compare our results to experiments and to scaling predictions.