Optical properties of sub-surface silver nanoparticulate films on 8 MeV electron beam irradiated polymer blends

Results of the investigations carried out on the optical properties of silver nanoparticulate films deposited on the electron beam irradiated blends of polystyrene (PS) and poly(4-vinylpyridine) (P4VP) are reported. Sub-surface silver particulate films are deposited at a constant deposition rate of 0.4 nm/s on irradiated blends held at 455 K in a vacuum of 8 × 10⁻⁶ torr. The optical absorption studies indicate that the morphology of the nanoparticulate films can be tuned by electron beam irradiation of polymer blends. The change observed due to irradiation is attributed to the formation of free radicals, thereby altering the polymer–metal interaction. A shift in the plasmon resonance peak towards longer wavelengths is observed for 50 nm thick silver particulate films deposited on softened 8 MeV electron irradiated P4VP as compared to unirradiated P4VP. The shift is more in the case of P4VP than for PS, possibly due to the combined effect of free radicals produced by irradiation and the lone pair of electrons present in P4VP in enhancing the metal–polymer interaction. The saturation of free radicals takes place in P4VP at doses higher than 25 kGy. Further, the results also indicate that the free radical creation due to irradiation is more in PS than in P4VP, as the saturation takes place at lower doses in a PS/P4VP blend as compared to P4VP and in a blend with higher PS content. X-ray diffraction studies on silver films deposited on unirradiated and irradiated, softened polystyrene substrates do not show any significant change due to irradiation.