Probe diffusion from dilute to concentrated in polyelectrolyte solution: salt effect

The adsorption behaviors between a positively charged poly(allyamine) hydrochloride (PAH) matrix and negatively charged sulfate polystyrene (PS) particle probe were investigated using dynamic light scattering (DLS) and fluorescence photobleaching recovery (FPR) with reference to the matrix and salt concentration. The system experienced a steep decrease of diffusion (flocculation) under dilute conditions and a gradual decrease above semidilute concentrations. The fluorescence photobleaching recovery and viscometry experiments revealed that the probe behaviors in the polyelectrolyte solution were strongly affected by the coil overlap concentration (0.5 g/L poly(allyamine) hydrochloride). Near the coil overlap concentration, the hydrodynamic radius representing the entanglement dimension of the matrix was approximately 30 nm; however, at higher concentrations the radius gradually decreased, suggesting a transition toward a network structure. In this system, the salt performed two roles: (1) reinforcing the electrostatic interaction, and (2) preventing electrostatic interaction between the probe and the matrix.