Dependency of Particle Sizes and Colloidal Stability of Polyelectrolyte Complex Dispersions on Polyanion Structure and Preparation Mode Investigated by Dynamic Light Scattering and Atomic Force Microscopy^†

Polyelectrolyte complex (PEC) dispersions were prepared by controlled mixing of three random copolymers of sodium 2-acrylamido-2-methylpropanesulfonate (AMPS) with either t-butyl acrylamide (TBA) [P(AMPS₅₄-co-TBA₄₆) and P(AMPS₃₇-co-TBA₆₃)] or methyl methacrylate (MM) [P(AMPS₅₂-co-MM₄₈)] with an ionene-type polycation, containing 95 mol % N,N-dimethyl-2-hydroxypropyleneammonium chloride repeat units (PCA₅), with their structural characteristics being deeply investigated by dynamic light scattering (DLS) and atomic force microscopy (AFM). Shape, size, and polydispersity of the PEC dispersions were directly observed by AFM as a function of polyanion structure, the ratio between charges, n^-/n⁺, and the titrant addition rate (TAR). The particle sizes increased and the colloidal stability decreased with the increase of the nonionic comonomer content and with the decrease of TAR. It was demonstrated that the medium particle sizes of the complex nanoparticles adsorbed on silicon wafers measured by AFM, in the dry state, were close but always lower than those measured by DLS, both before and after the complex stoichiometry.