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 (Ma) of SPS and the content of C60. When the Ma of SPS was smaller than the critical molecular weight for the entanglement (Mc) 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 Ma was larger than the Mc 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 (Mw) of LPS was smaller than the Mc of PS, and the η* at low shear frequencies of LPS/C60 was lower than that of pure LPS when the Mw of LPS was larger than the Mc 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.