A systematic study of the stabilization in water of gold nanoparticles by poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymers

Poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO)(x)-(PPO)(y)-(PEO)(x) triblock copolymers have been efficiently used for the stabilization of gold nanoparticles (AuNps) in NaCl aqueous solutions. The effects of concentration and structure of the block copolymer (i.e., PEO block length, PPO block length, and overall length of the polymer) have been systematically investigated, using well-defined AuNps (diameter similar to 12 nm) synthesized through a standard citrate reduction procedure. Aggregation and precipitation processes were assessed separately using empirical parameters calculated from optical absorbance spectra. Increasing the concentration, PEO and PPO block lengths, or the overall length of the polymer enhanced the nanoparticles colloidal stability. Among all these parameters, the paramount one appeared to be the length of the PPO block. Different aggregation states were observed and characterized by the displacement of the plasmon resonance band. A correlation between the displacement of this band and precipitation of the nanoparticles was established.