Melt viscosity behavior of C60 containing star polystyrene composites

Abstract

The melt viscosity behavior of three-arm and six-arm star polystyrene (SPS)/C₆₀ composites was studied. It was found that the changing trend in the melt viscosity of SPS/C₆₀ composites depended on the molecular weight of the arm chain (M_a) of SPS and the content of C₆₀. When the M_a of SPS was smaller than the critical molecular weight for the entanglement (M_c) of polystyrene (PS), the complex viscosity obtained at 0.05 rad s⁻¹ (η^*_0.05) of SPS/C₆₀ composites with a low content of C₆₀ was lower than that of pure SPS. When the M_a was larger than the M_c of PS, however, the η^*_0.05 of the SPS/C₆₀ composites was higher than that of pure SPS. These results were contrary to the previous work on the melt viscosity behavior of linear PS (LPS)/C₆₀ composites (A. Tuteja et al., Macromolecules, 2007, 40, 9427–9434), where the η* at low shear frequencies of LPS/C₆₀ composites was higher than that of pure LPS when the molecular weight (M_w) of LPS was smaller than the M_c of PS, and the η* at low shear frequencies of LPS/C₆₀ was lower than that of pure LPS when the M_w of LPS was larger than the M_c of PS. The possible mechanism behind the melt viscosity behavior of SPS/C₆₀ composites was discussed. It was expected that the topological structure of SPS induced a more heterogeneous dispersion of C₆₀ in the SPS matrix than the dispersion state of C₆₀ in the LPS matrix. When the molecular weight of SPS was different, the contact states between SPS and C₆₀ might also be different, which would make C₆₀ act as a lubricator or barrier, leading to the reduction or increase of the melt viscosity of SPS/C₆₀, respectively.