Electrostatic Interactions and Stability of Poly-l-lysine Covered Polystyrene Latex Particles Investigated by Dynamic Light Scattering

Adsorption isotherms of the pH dependent positively charged polyelectrolyte poly-l-lysine (PLL) on negatively and positively charged polystyrene latices are determined. With photon correlation spectrometry (PCS) the influence of the fluctuating PLL domaines in solution on the diffusion coefficient is observed at low salt concentrationsc_NaBr< 10⁻³M with λ =c_PE/c_NaBr< 0.1 (c_PE= concentration of the polyelectrolyte units). Screening of the charged layer by increasing electrolyte concentration results in large adsorbed amounts and layer thicknesses. At low molar mass of PLL the suspensions become unstable and the state and kinetic of flocculation is followed by the decreasing diffusion coefficient. PLL of higher molar mass (M_w≥ 100 000) stabilizes the particles sterically and the adsorbed layer thicknesses can be determined. The conclusions drawn from PCS features are confirmed directly by raster electron micrographs of the filtered particles.