Influence of Poly(sodium 4-styrenesulfonate) on the Optical Response of Reduced Graphene Oxide Thin Films

Graphene-based nanocomposites stabilized with polymers are emerging as promising materials for optoelectronic applications due to their tunable optical and structural properties. In this study, we investigate and compare the optical behavior of graphene oxide (GO), thermally reduced graphene oxide (RGO), and RGO films functionalized with poly(sodium 4-styrenesulfonate) (PSS). Thin films were deposited by dip-coating aqueous dispersions onto SiO₂/Si substrates and characterized using Variable Angle Spectroscopic Ellipsometry (VASE) in the 0.38–4.1 eV photon energy range. The dielectric response of GO and RGO films was modeled using three Lorentz oscillators, reflecting transitions associated with oxygenated functional groups and partial restoration of sp² hybridization. Conversely, the optical properties of PSS-RGO films are described by a single Lorentz oscillator at approximately 2.8 eV and a pole, indicating the formation of new electronic states likely arising from the improved ordering of sp² carbon domains during reduction in the presence of the polymer. Scanning Electron Microscopy (SEM) analysis reveals that PSS enhances the homogeneity and compactness of the films, preventing aggregation and promoting uniform coverage. These findings highlight the critical role of PSS as a functional matrix capable of modulating both the morphology and optical response of RGO, particularly in the extended near- and mid-infrared spectral range.