Nanoscale Research Letters
PEDRO JOSE RIVERO; JAVIER GOICOECHEA; AITOR URRUTIA; IGNACIO RAÚL MATIAS; FRANCISCO JAVIER ARREGUI
In the present study, we show that silver nanoparticles (AgNPs) with different shape, aggregation state and color (violet, green, orange) have been successfully incorporated into polyelectrolyte multilayer thin films using the layerby-layer (LbL) assembly. In order to obtain colored thin films based on AgNPs is necessary to maintain the aggregation state of the nanoparticles, a non-trivial aspect in which this work is focused on. The use of Poly(acrylic acid, sodium salt) (PAA) as a protective agent of the AgNPs is the key element to preserve the aggregation state and makes possible the presence of similar aggregates (shape and size) within the LbLcolored films. This approach based on electrostatic interactions of the polymeric chains and the immobilization of AgNPs with different shape and size into the thin films opens up a new interesting perspective to fabricate multicolornanocomposites based on AgNPs.
Fabrication of the multilayer film
Aqueous solutions of PAH and PAA with a concentration of 25 mM with respect to the repetitive unit were prepared using ultrapure deionized water (18.2 MΩ · cm). The pH was adjusted to 7.5 by the addition of a few drops of NaOH or HCl. The LbL assembly was performed by sequentially exposing the glass slide (substrate) to cationic polyelectrolyte poly(allylamine hydrochloride) (PAH) and anionic polyelectrolyte PAA loaded with the silver nanoparticles previously synthesized (PAA-Ag NPs) with an immersion time of 5 minutes. A rinsing step of 1 minute in deionized water was performed between the two polyelectrolytes baths and a drying step of 30 seconds was performed after each rinsing step. The combination of a cationic monolayer with an anionic monolayer is called bilayer. The LbL process was carried out using a 3-axis cartesian robot from Nadetech Innovations.