Relationship between rheological and electrical percolation in a polymer nanocomposite with semiconductor inclusions

Microstructure, electrical conductivity, and rheological properties of nanocomposites based on isotactic polypropylene (iPP) containing semiconductor nanoparticles of TiO2 were studied. Compatibilized and uncompatibilized nanocomposites containing a wide range of TiO2 concentrations (up to 15 vol%) were prepared by melt compounding in a twin-screw extruder via a masterbatch method. An anhydride-modified PP (AMPP) was used as the compatibilizer. Atomic force microscopy (AFM), scanning electron microscopy (SEM), and image analysis techniques were utilized to study the morphology evolution in the samples. Analyzing the results of direct current (DC) electrical conductivity measurements showed a lower percolation threshold for the uncompatibilized samples, compared to the compatibilized ones. In order to estimate the percolation threshold, linear and nonlinear melt-state viscoelastic properties of the samples were studied. Liquid-solid transition and nonterminal behavior of the uncompatibilized samples were observed at relatively lower range of TiO2 loading, compared to the compatibilized samples. It was an indication of lower rheological percolation threshold in the uncompatibilized nanocomposites which was in agreement with the electrical percolation threshold. Scaling analysis of strain sweep tests above the percolation thresholds of the nanocomposites resulted in a lower fractal dimension for the uncompatibilized samples.