Dispersion state of carbon black in polystyrene produced with different dispersion media and its effects on composite rheological properties

The dispersion state and aggregate structure of carbon black in polystyrene composites prepared by solvent casting suspensions in different dispersion media, i.e., chloroform, tetrahydrofuran, and toluene, with different particle contents and their effects on the bulk rheological properties of the composites were investigated by transmission electron microscopy, ultrasmall-angle and small-angle X-ray scattering, and dynamic viscoelasticity measurements. The macroscopic dispersion state of carbon black in the solvent-cast films was largely affected by the dispersion medium, reflecting the stability of the suspension in the polystyrene solution. The mass fractal dimension of carbon black in the polymeric matrix, which was evaluated by X-ray scattering techniques with a resolution of nanometers, tended to exhibit a higher value for the dispersion media with less carbon black dispersibility. The surface fractal dimension of carbon black in the polymer was independent of the dispersion medium and exhibited a lower value than carbon black powder due to physical adsorption of the polymer on the particle surface. The viscoelastic moduli for the melt polymer composites below and above the percolation limit varied according to the dispersion media, reflecting the difference in the macroscopic dispersion state and aggregate structure of carbon black in polystyrene.