Counterion structure and dynamics in polyelectrolyte solutions

Investigations of the counterion distribution and correlations to polyelectrolytes have seen increased activity to understand intrinsically stiff and flexible polyelectrolytes in good solvents as functions of ionic strength, charge valence, and concentration. In particular, anomalous (resonant) small-angle X-ray scattering and small-angle neutron scattering have provided new insights on counterion association/condensation. An area of expected growth is counterion dynamics studied via techniques such as electron paramagnetic resonance and neutron-spin echo spectroscopy where the counterion can be labeled along with pulsed-field gradient nuclear magnetic resonance, which can examine a wide range of time and length scales. Along with these experimental studies, theory and simulations provide important predictions and insight.