One-step synthesis of poly(ethylene oxide)/gold nanocomposite hydrogels and suspensions using gamma-irradiation

Poly(ethylene oxide) (PEO)/gold nanocomposite hydrogels and suspensions were synthesized by gamma-irradiation of PEO and Au3+ aqueous solutions to a dose of 50 kGy under inert atmosphere and without addition of 2-propanol, depending on the initial concentration of Au3+ and pH of solutions. The pH of the initial solutions had the major influence on the formation of PEO/Au nanocomposite hydrogels vs. suspensions. The pH and Au3+ initial concentration determined the AuNPs size and suspension stability, as determined by UV-Vis spectroscopy. The neutral pH favored the formation of stable suspensions with the smallest gold nanoparticles (AuNPs), whereas unstable suspensions and bigger nanoparticles (NPs) were obtained at acidic pH and by increasing Au3+ initial concentration. On irradiation at alkaline conditions PEO/AuNPs hydrogels were produced in one-pot synthesis method - by simultaneous crosslinking of PEO chains and reduction/synthesis of Au nanoparticles. Scanning electron microscopy of nanocomposite gels revealed the gold nanoparticles embedded in PEO matrix with homogenous distribution. The thermal and viscoelastic properties of PEO/AuNPs gels depended on the initial Au3+ concentration, that is on amount of AuNPs synthesized inside gels. Lower particle content resulted in gels with generally higher melting and crystallization temperatures as well as higher storage moduli, yield points and flow points than pure PEO gel. The optimal amount were up to 1 wt% Au for obtaining stronger gels, whereas higher amount of NPs, because of NPs agglomeration, lead to deterioration of gel properties and significant weakening of gel.