Polyelectrolyte complexation in brushes

Anionic polystyrene sulfonate (PSS) chains were grafted from mica surfaces to create dense brushes for use in surface force (SFA) measurements. These surfaces were mounted in the SFA embedded in an aqueous solution environment of low ionic strength into which the cationic homopolymer, poly[(vinylbenzyl) trimethylammoniumnitrate] (PVBTMAN), is introduced. Before the introduction there are long range repulsive forces between the PSS brushes as we have frequently documented before. Interestingly, the introduction of PVBTMAN initially produces an increase in the range of the purely repulsive forces. However, with addition of a further amount of PVBTAN and/or additional waiting time under compression, the range of the forces shrinks and attractive forces appear on separation. These different stages appear to arise from different stages of penetration of the cationic homopolymer into the anionic brush.