Rodlike Behavior of Polyelectrolyte Brushes

Spherical charged brushes are studied in the form of block copolymer micelles. These copolymers are diblocks made of one deuterated, highly charged block and of one protonated, hydrophobic block. Neutron scattering with contrast matching enables us to probe selectively the structure of the arms of the charged corona of the micelles. A near-perfect rodlike behavior (scattered intensity $\sim q^{-1\mathrm{}}$) of the arms is observed at all salt concentrations above an onset in wave vector $q_0$, which increases with salt concentration above a threshold. Results are strikingly different from what is observed for linear polyelectrolytes, since charged brushes appear very weakly sensitive to the addition of salt.