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Abstract: We report the formation of stable nanoparticle-polymer clusters obtained byelectrostatic complexation. The nanoparticles placed under scrutiny arenanoceria CeO2 coated by short polyacrylic acid moieties, whereas thepolymers are cationic-neutral block copolymers. The cluster formation wasmonitored using different formulation pathways, including direct mixing,dialysis, dilution and quenching. In the first process, the hybrids wereobtained by mixing stock solutions of polymers and nanoparticles. Dialysis anddilution were based on controlled desalting kinetics according to methodsdeveloped in molecular biology. The fourth process consisted in a rapiddilution of the salted dispersions and as such it was regarded as a quench ofthe cluster kinetics. We have found that one key parameter that controls thekinetics of formation of electrostatic clusters is the rate dIS-dt at which thesalt is removed from the solution, where IS denotes the ionic strength. Withdecreasing IS, the electrostatically screened polymers and nanoparticles systemundergo an abrupt transition between an unassociated and a clustered state. Bytuning the desalting kinetics, the size of the clusters was varied from 100 nmto over 1 micrometer. At low ionic strength, the clusters were found to bekinetically frozen. It is proposed that the onset of aggregation is driven bythe desorption-adsorption transition of the polymers onto the surfaces of theparticles.

Autor: J. Fresnais, C. Lavelle, J.-F. Berret


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