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

The influence of the formulation process/pathway on the generation of electrostatic 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 latter depends on the mixing pathway and was investigated in a previous publication by tuning the mixing order and/or speed (Qi, L.; Fresnais, J.; Berret, J.-F.; Castaing, J.-C.; Grillo, I.; Chapel, J.-P. J. Phys. Chem. C 2010, 114 (30), 12870-12877). The former depends on the initial concentration of the individual stock solutions and the strength of the interaction and is investigated here on a system composed of anionic cerium oxide functional nanoparticles (CeO2-PAA) and cationic charged-neutral diblock copolymers (PTEA11K-b-PAM30K) or homopolyelectrolytes (PDADMAC100K). The electrostatic interaction was screened off completely by adding a large amount of salts. Desalting kinetics was then controlled by slowly decreasing the ionic strength from Ib?0.5 M, the minimum ionic strength to totally prevent the complexation of the two components, to lower values where the electrostatically screened system undergoes an (abrupt) transition between an unassociated and a clustered state. Neutron scattering
data evidenced differences in the nanostructure of complexes formed by either dilution or simple mixing. Furthermore, adsorption optical reflectometry experiments showed the impact of these different formulation processes on the wettability and antifouling properties of treated silica and polystyrene model surfaces. Better controlled mixing processes were put forward at the end to improve the productivity and reproducibility of the complexes generation. In particular, a microfluidic chip coupled with dynamic light scattering was used
to better control the hydrodynamics of the complexation process.