(365a) Direct Measurement of Forces between Poly(sodium-4-styrene sulfonate) Brushes on Mica Immersed in Aqueous Solutions of Poly(vinyl benzyl trimethylammonium nitrate)

When polyelectrolyte solutions of opposite charge are mixed, they form polyelectrolyte complexes resulting in phase separation of the bulk solution into a polymer-rich phase and a polymer-dilute phase. Similar complexation occurs between polyelectrolyte brushes in the presence of oppositely charged polyelectrolyte species in solution. In this work, we use the surface forces apparatus (SFA) to probe how the force profile of two apposing, polyanionic brushes evolve as polycations are introduced into the aqueous phase separating the two brushes. The polyanion and polycation of interest are poly(sodium-4-styrene sulfonate) (PSSNa) and poly(vinylbenzyl trimethylammonium nitrate) (PVBTMAN), respectively. We compare force profiles of PSSNa brushes in pure water with those of PSSNa brushes in aqueous solutions of PVBTMAN at different molar ratios to observe a reduction in height of the resulting PSSNa-PVBTMAN complex as molar ratio increases. Additionally, we compare atomic force microscopy (AFM) height traces of PSSNa brushes with those of PSSNa-PVBTMAN complexes. We also report SFA and AFM measurements in aqueous solutions containing potassium bromide, a salt that destabilizes PSSNa-PVBTMAN complexes in the bulk phase, to study its effect on the force profiles and morphology of polyelectrolyte brush complexes.