Untightening constrained segments of charged polymers at interfaces

The effect of dipole-dipole interaction between the ion-pairs within a highly charged polyelectrolyte brush has been investigated. The introduction of external salt is discovered to break up dipole-dipole multiplets and make the previously constrained segments released. This is demonstrated by the measurements by neutron reflectivity with a model system (sodium polystyrene sulfonate), showing that its segmental density profile is further expanded into the aqueous media when the salt concentration in increased to a moderate value. Meanwhile, dielectric spectroscopy demonstrate increase of segmental relaxation frequency. All of these results clearly demonstrated an obvious effect created by dipole-dipole interaction, besides the dominating role of electrostatic interaction.