Synthesis and association of Ag(0) nanoparticles in aqueous Pluronic F127 triblock copolymer solutions

Triblock copolymers poly(ethylene oxide) (PEO)–poly(propylene oxide) (PPO)–poly(ethylene oxide) (PEO) Pluronic F127 was employed as capping agent for the Ag(0) metallic nanoparticles synthesized by the chemical reduction of silver nitrate, AgNO3, with excess of sodium borohydride, NaBH4. The morphology and the kinetics of Ag(0) nanoparticles were studied by transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic light scattering (DLS), UV–vis absorption and fluorescence probe technique. Spherical polydisperse particles of 12 ± 4 nm mean diameter at varying the Pluronic concentration in the range of 0.13–13 wt.% were reported. Apart from the stabilizing role, the triblock copolymer promoted the agglomeration of individual Ag(0) nanoparticles in small assemblies whose plasmon band features differed from those of the individual nanoparticles. The formation of Ag(0) nanoparticles–F127 complex took place after full reduction of the Ag+ ions and it was controlled by the F127 concentration. The nanoparticle morphology and the fluorescence probe technique suggested that the excess Pluronic drove indirectly the Ag(0) nanoparticles association. Free F127 polymeric micelles encountered above critical micellar concentration (cmc) promoted the partial desorption of the adsorbed triblock copolymer and subsequently weakened the stability of the individual nanoparticles.