Structural Characteristics and Bonding Environment of Ag Nanoparticles Synthesized by Gamma Irradiation Within Thermo-Responsive Poly(N-isopropylacrylamide) Hydrogel

Abstract

To produce well-defined metal clusters stabilized in protective matrix, poly(N-isopropylacrylamide) (PNi-PAAm) hydrogel with different initial concentration of polymer was used as nanoreactor. The in situ synthesis of well dispersed silver nanoparticles (AgNPs) was performed by gamma irradiation. The obtained AgNPs are spherical in shape with the diameter less than 20 nm. Crystalline properties of nanoparticles such as size, texture coefficient, strain, stress, lattice parameter, d-spacing, and dislocation density have been calculated using XRD data. Results confirm that the changes of lattice parameter of crystalline AgNPs sensitively reflect their state of strain and stress depending on the formation conditions (i.e., on the concentration of PNiPAAm) and on the diameter of AgNPs. The negative lattice strain and compression stress were observed for the smaller AgNPs (lattice contraction), while for the larger AgNPs are positively strained and under tensile stress (lattice expansion). XPS spectra revealed the donor-acceptor type of interaction between carbonyl oxygen from PNiPAAm and AgNPs (positive shift of high BE component of O 1s and negative shift of Ag 3d BE). The greater dislocation density of smaller AgNPs incorporated in more concentrated PNiPAAm, resulted in more binding sites and stronger interaction with polymer.