Rheological percolation in polystyrene composites filled with polyaniline-coated multiwall carbon nanotubes

• Multiwall carbon nanotube/polyaniline core/shell nanofibers were synthesized.
• PANi-coated MWCNTs dispersed better in polystyrene than bare MWCNTs.
• PANi-coated MWCNTs has lower electrical percolation than bare MWCNTs.
• Rheological percolation occurs at higher loadings than electrical percolation.
• Gel network for solution-mixed sample is stiffer than melt-mixed.

Polyaniline (PANi)-coated multiwall carbon nanotubes (MWCNTs) and uncoated MWCNTs were added to a polystyrene (PS) matrix using solution and melt mixing. Electrical and rheological measurements were carried out on polymer composites to study the mechanism of conductive network formation. This work reveals the effect of nanofiller's coating on network formation using both rheological and electrical techniques. PANi-coated MWCNTs exhibit a much lower electrical percolation threshold (0.4 wt%) than uncoated MWCNTs (0.7 wt%), due to better dispersion of PANi-coated MWCNTs in a PS matrix. Dispersion of nanofillers in a polymer matrix was studied using optical microscopy and differential scanning calorimetry (DSC). Rheological characterizations of composite samples revealed a percolation behavior at higher concentration than that found electrical percolation. The inverse of damping factor (G′/G″) was the best parameter to elucidate the percolation threshold in a polymeric composite (i.e. PANi-coated MWCNT in PS had electrical percolation of 0.40 wt% and rheological percolation 0.52 wt%). A better affinity of PANi with PS led to better dispersion of nanofillers and lower rheological percolation for PS/MWCNT-PANi composites than those seen for PS/MWCNT composites.