Adsorption mechanism of a weak polyelectrolyte, PAH, onto carboxylate PS particles

The different adsorption behavior of a weak polyelectrolyte, poly(allyamine hydrochloride) (PAH), onto weakly charged particles, carboxylate polystyrene (PS) latex, was investigated using static and dynamic light scattering (SLS and DLS) in solutions with different pH. Carboxylated PS particles existed in severe flocculation at pH 3, while particles are retained in a relatively stable dispersion state at pH 10 due to the variation of surface charge density. Aggregated particles fully disappeared as the concentration of PAH increased at pH 3, but weakly flocculated particles were still retained at pH 10. The scattering intensity increased at pH 3 while that at pH 10 decreased near the coil overlap concentration (0.5 g/l PAH concentration). The ζ-potentials of the samples at different pH conditions showed unusual shifts. These different dispersion/flocculation phenomena were explained in terms of the balance of electrostatic and van der Waals interactions between the weakly charged particles and the polyelectrolyte.