Interactions between planar stiff polyelectrolyte brushes

Molecular-dynamics simulations were performed for two opposing flat surfaces sparsely grafted with rigid polyelectrolyte chains whose lengths are smaller than their persistence lengths. The resulting force-distance dependence was analyzed theoretically in terms of two separate physical mechanisms: the pressure arising from osmotically active counterions trapped within the brush and the work required to bend the brush chains under confinement, which can be accurately characterized by a ground-state theory of rigid polymer buckling. These contributions are of the same magnitude and should be distinguishable in experiments of double-stranded DNA brushes.