The effect of polymer molecular weights on the electrical, rheological, and vapor sensing behavior of polycarbonate/multi-walled carbon nanotube nanocomposites

Conductive polymer composites (CPCs) based on polycarbonate/multi-walled carbon nanotubes (PC/MWCNT) were fabricated by melt mixing. By selecting the PCs with different molecular weights, three kinds of PC/MWCNT composites were obtained. The CPCs containing low viscous PC (lPC) had the lowest percolation threshold (0.06 vol%) as compared to those of medium viscous PC (mPC) (0.07 vol%) and high viscous PC (hPC) (0.13 vol%), which was attributed to the best MWCNT dispersion in matrix. Light microscopy images also demonstrated that lPC/MWCNT composite had the smallest undispersed filler agglomerates than the other two corresponding PC/MWCNT composites with the same filler loading (0.25 wt%). In terms of rheological measurements, rheological percolation occurred at a lower filler content for lPC/MWCNT than mPC/MWCNT and hPC/MWCNT composites. The chemo-resistive properties of composites towards organic vapors were investigated by measuring relative resistance change of CPCs upon vapor immersion-drying cycles. CPCs exhibited different sensing tendencies towards different organic vapors. lPC based CPCs exhibit higher relative resistance change as compared to mPC and hPC based CPCs because of their loosely overlapped conductive network, which are easily changed under polymer swelling. Besides, sample thickness is another factor that determined the vapor sensing performance of CPCs. Furthermore, relative resistance change of composites is found to be closely related with vapor concentration. This work presents a new thought in understanding filler dispersion in PC with different molecular weights, which has implication of turning conductive network structure and sensing performance of composites.

Automated summary

Conductive polymer composites based on polycarbonate/multi-walled carbon nanotubes were fabricated by melt mixing with different molecular weight polycarbonates. The composites with low viscous polycarbonate showed the lowest percolation threshold and best filler dispersion in the matrix, leading to better sensing performance towards organic vapors. This study provides insight into how filler dispersion in polycarbonates with different molecular weights affects the conductive network structure and sensing properties of the composites.