INFLUENCE OF POLYELECTROLYTES ON THE SURFACE ELECTROSTATISTICS OF CHARGED COLLOIDS AS DETERMINED USING H-2 NMR

The effects of the anionic polyelectrolyte poly(sodium styrenesulfonat e) (PSSS) on the surface electrostatic charge of polystyrene particles bearing a preformed monolayer of surfactants have been investigated u sing deuterium (H-2) nuclear magnetic resonance (NMR) spectroscopy. Th e initial particle surface charge density was manipulated by mixing th e zwitterionic surfactant hexadecylphosphocholine (HDPC) with a cation ic surfactant, cetyltrimethylammonium bromide (CTAB). The H-2 NMR spec trum from deutron labels attached to the phosphocholine group of HDPC (HDPC-gamma-d6) showed the presence of ''bound'' HDPC-gamma-d6 in the form of a broad, axially symmetric Pake pattern characterized by a uni que quadrupole splitting. The size of the quadrupole splitting increas ed with increasing amounts of CTAB and decreased with increasing amoun ts of PSSS. Conversion of the quadrupole splittings to surface charge densities showed that flocculation of the latex by PSSS occurred much prior to neutralization of the initial surface charge due to CTAB. The level of PSSS binding increased in proportion to the level of CTAB. H igh PSSS binding was accompanied by indications in the H-2 NMR spectra of hindered molecular dynamics at the particle surface.