Revisiting the structural and functional properties of polystyrene–silica nanocomposites: optical bandgap modulation and photoluminescence properties
摘要
In this study the structural, optical, and dielectric properties of polystyrene (PS) and silica (SiO2)-based nanocomposites were investigated. PS/SiO2 nanocomposites were synthesized via combination solution blending and hot pressing method. X-ray diffraction (XRD) analysis confirms the amorphous nature of both the polymer and filler. No significant crystallization was observed upon silica incorporation into the polymer matrix. Morphological analysis realized via scanning electron microscopy (SEM) and atomic force microscopy (AFM), which reveals that silica nanoparticles up to 5 wt% are well-dispersed. However, higher concentrations of silica result in agglomeration, leading to structural heterogeneity. Optical absorption measurements in ultraviolet–visible region demonstrate that increasing SiO2 content reduces the direct bandgap from 4.39 eV (pure PS) to 4.25 eV (PS/5% SiO2) and the indirect bandgap from 3.75 to 3.69 eV. This result indicating the formation of localized electronic states at the polymer–nanoparticle interface. The Urbach energy increases from 0.18 eV (pure PS) to 0.22 eV (PS/10% SiO2), signifying higher disorder at elevated filler loadings. Photoluminescence (PL) analysis reveals additional emission peaks at 405 nm, 433 nm, and 465 nm, associated with oxygen-deficient centers on the silica surface and suggest their role in modifying the electronic transitions of the composite. Dielectric spectroscopy reveals that the relative permittivity increases from 2.6 (pure PS) to 4.1 (PS /10% SiO2) at 1 kHz, attributed to enhanced interfacial polarization and the intrinsic polarizability of silica nanoparticles. The dielectric loss tangent exhibits minimal variation with increasing filler content. This fact indicates that the composites maintain their insulating properties across a broad frequency range.