EFFECT OF THE PH ON STRUCTURE OF ASSOCIATION BETWEEN NANOPARTICLES AND POLYELTROLITY

Cerium oxide nanoparticles or nanoceria self-assembled through the layer-by-layer (LbL) technique have been investigated as sensors.1 For nanoceria stabilized with a weak polyelectrolyte is expected that the pH influences both, the characteristics of species in solution and the structure of the formed film.2 Then, the goal of this study is to establish a correlation between the parameter pH of the solution and the characteristics of the charged species in the solution that interact to form aggregates or coacervates on the solution. For that, solutions of poly(diallyl dimethylammonium chloride), PDADMAC, and CeO2 nanoparticle, NP-CeO2, coated by polyacrylic acid were prepared at pH 4, 7, and 9 at concentrations of 10 and 1mM, respectively. Hydrodynamic diameter (DH, nm) and zeta potential (ZP, mV) measurements were performed in Litesizer equipment (model 500, Anton-Paar) for nanoparticle solutions coated or not. Also, aliquots of PDADMAC solution were added stepwise to nanoparticle solutions followed by DH and ZP measurements. The bare nanoparticles used in this study are stabled just in acid conditions of pH lower than 2, showing ZP and DH of +27,6 mV and 12,1 nm, respectively. After the stabilization with polyacrylic acid, the nanoparticles become negatively charged and then can be used in a wide pH range. However, it is observed that ZP and hydrodynamic diameter vary according to the solution’s pH. Decreases in pH solution increase the particle sizes and decrease the ZP values. For nanoparticle interactions with PDADMAC, it was observed that the pH influences the stoichiometry of the complexation.