Synthesis, characterization and properties of polystyrene/NiO nanocomposites

In this study, polystyrene (PSt)/NiO nanocomposites (NCs) were prepared in three stages. First, NiO₂ was prepared by the reaction of Ni(NO₃)₂⋅6H₂O with sodium hypochlorite in the present of CTAB in alkaline solution, and then its oxidation by ethanol, obtained NiO nanoparticles (NPs). Second, the surface of NiO NPs was modified in order to obtain better dispersity and proper compatibility in organic media by oleic acid. Surface modification of NiO NPs was confirmed through lipophilic degree (LD). The results revealed that LD increased with the rising amount of modifier up to 5 wt%. Optimum modification was obtained at 65 °C and 4 h for reaction time. Third, the modified NiO NPs were dispersed in styrene monomer, and PSt/NiO NCs were synthesized via miniemulsion polymerization. The NiO NPs, its modified NPs and PSt/NiO NCs were characterized by XRD, FT-IR, FE-SEM, EDX, XPS and VSM. The average crystallite sizes of NiO were calculated to be 14 nm from XRD patterns. The results of EDX analysis and FT-IR spectra showed that chains of oleic acid have been successfully grafted on surface of NiO NPs. The morphological observation revealed that NiO NPs were embedded homogeneously in the inner part of polystyrene. Thermal stability of PSt/NiO NCs was studied using techniques of TGA and DSC. Compared to polystyrene, PSt/NiO NCs prepared by this method increased the glass transition temperature to 29 °C and increased the thermal degradation temperature that to 45 °C. The VSM results showed that the NiO NPs and PSt/NiO NCs have super paramagnetic properties.