Association of polymers and nanoparticles in the production of multilayer films

Layer-by-layer (LbL) is a thin film deposition technique that can be applied to incorporate nanoparticles and obtain functional materials, such as those used in developing sensors. This study utilized the LbL technique to fabricate structured films from cerium oxide nanoparticles (CeO₂) coated with poly(acrylic acid) (PAA_2k), termed NP-CeO₂-PAA_2k, and the cationic polyelectrolyte poly(diallyldimethylammonium chloride) (PDADMAC). Prior to the LbL process, the aqueous dispersion of the PAA2k-coated nanoparticles was characterized to determine the hydrodynamic diameter (D_H) and the zeta potential (ζ). The results indicated that both D_H and ζ varied with pH. Specifically, D_H values were 72 nm, 21 nm, and 17 nm, while ζ values were -26 mV, -49 mV, and -55 mV for pH of 4, 7, and 9, respectively. The interaction between NP-CeO₂-PAA_2k and PDADMAC in aqueous solution was analyzed based on the charge ratio Z_+/- for values ranging from 0 to 1.8 and pH values of 4, 7, and 9. The critical ratio indicating the onset of precipitation of the studied species was determined. The LbL assembly was performed on commercial glass surfaces pre-treated with strong aqueous base solutions (potassium hydroxide, KOH) or modified with 3-aminopropyltrimethoxysilane (APTES). Surface analysis of these glasses involved measuring ζ through electrokinetic measurements. The optimal substrate for LbL film growth was the glass treated with KOH, which had a ζ value of -76 mV. The growth of the (PDADMAC/NP-CeO₂-PAA_2k)n film, with n up to 5 bilayers, was monitored using ultraviolet-visible (UV/Visible) spectroscopy. An increase in absorbance with the number of bilayers indicated the successful incorporation of NP-CeO₂-PAA_2k into the films.