Structural characteristics of Ag nanoparticles synthesized in situ within pnipaam hydrogel by γ-irradiation

In this work, silver nanoparticles (AgNPs) are synthesized within thermo responsive poly(N-isopropylacrylamide) (PNiPAAm) hydrogels of different concentrations, by γ-irradiation. The UV-Vis plasmon absorption characterization of AgNPs and its modeling using Mie theory showed that their diameters are less than 20 nm. The X-ray diffraction (XRD) data are consistent with the face centered cubic (FCC) crystal structure of bulk metallic Ag. The negative lattice strain (lattice contraction) was observed for the samples where the AgNPs are incorporated in the xerogel solid matrix of highest polymer concentration (15 wt.% PNiPAAm). The lattice parameter values are found to be higher than the bulk lattice parameter of Ag for larger nanoparticles formed in 5 wt.% PNiPAAm, whereas the crystallites were under tensile stress. On the other hand, for smaller nanoparticles formed in 15 wt.% PNiPAAm, crystallites were under compression stress (negative stress) whereby the lattice is contracted.