Charge Reversal of Sulfate Latex Particles by Adsorbed Linear Poly(ethylene imine) Probed by Multiparticle Colloidal Probe Technique

Interactions between negatively charged latex particles in the presence of cationic linear poly(ethylene imine) (LPEI) were studied with atomic force microscopy (AFM) and electrophoresis. Forces were measured directly with the recently developed multiparticle colloidal probe technique, which permits colloidal particles to attach to the cantilever in aqueous dispersions in situ and ensures a large surface area during experiment. It was observed that the forces vary from repulsive to attractive and back to repulsive with increasing polymer dose. The repulsive forces are due to overlap of the diffuse layers around charged surfaces. The attractive forces are independent of the ionic strength and the molecular mass of the polymer and can be rationalized in terms of classical van der Waals interactions. Additional electrostatic attractive forces due to patch-charge heterogeneities observed in other particle–polyelectrolyte systems are absent here. Their absence indicates that the adsorbed layer of LPEI has a high lateral homogeneity

Repulsion exerted on a spherical particle by a polymer brush

The steric repulsion exerted on spherical particles by a semidilute polymer brush is evaluated using numerical self-consistent field theory (SCFT) in cylindrical coordinates. This accurate treatment provides the opportunity to test the conventional analytical approach, where the strong-stretching theory (SST) of Milner, Witten, and Cates for uniform compression can be adapted to particles of any shape using the Derjaguin approximation. While the Derjaguin approximation works well, at least, for the interaction energy, the SST proves to be seriously inaccurate for realistic grafting densities. Nevertheless, an efficient and accurate treatment for arbitrarily shaped particles remains possible if the uniform compression in the Derjaguin approximation is supplied by SCFT.close464