Influence of the Formulation Process in Electrostatic Assembly of Nanoparticles and Macromolecules in Aqueous Solution: The Mixing Pathway

The influence of formulation process/pathway on the generation of electrostatically coassembled complexes made from polyelectrolyte-neutral copolymers and oppositely charged nanocolloids is investigated in this work. Under strong driving forces like electrostatic interaction and/or hydrogen bonding, the key factor controlling the polydispersity and the final size of the complexes is the competition between the reaction time of the components and the homogenization time of the mixed solution. The former depends on the initial concentration of the individual stock solutions and the nature of the interaction and will be investigated in a forthcoming publication; the latter depends on the mixing pathway and is put under scrutiny here on a system composed of cerium oxide nanoparticles and charged-neutral diblock copolymers (CeO2/PSS7K-b-PAM(30K)) by tuning the mixing order and/or speed. The resulting structures generated from various formulation processes were characterized by light and neutron scattering techniques. The complexes final morphologies (size, shape, polydispersity) were found to depend strongly on the formulation process, while keeping at a smaller scale (clusters) the same nanostructure. Finally, the impact of those different structures on some bulk (rheology) and surface (wetting/antifouling) properties was evaluated. These results highlighted that a process-dependent formulation seen a priori as a drawback can be turned into an advantage: different properties can be developed from different morphologies while keeping the chemistry constant.