Influence of molar mass and temperature on the dynamics of network formation in polycarbonate/carbon nanotubes composites in oscillatory shear flows

The influence of molar mass and temperature on the formation of networks of multiwalled carbon nanotubes (MWCNT) in oscillatory shear flows was investigated. Combined rheological and electrical investigations were performed using composites with 0.5-5.0 wt% MWCNT in a low- and a high-viscosity polycarbonate (PC) at 190 °C and 250 °C. The objective of this work was to study the dynamics of the simultaneous formation of electrical and rheological networks by taking into account the superposition of (i) network breakup by the applied shear field and (ii) the diffusion-controlled clustering of carbon nanotubes. The formation (i.e. the buildup) of electrical and rheological networks proceeds more rapidly for a lower-viscosity matrix and at higher temperatures, whereas breakup of the electrical network is more pronounced at lower temperatures because of a larger stress-transfer between polymer matrix and MWCNT network. Sinusoidal shear deformation results in an oscillatory electrical conductivity with decreasing average value at large shear amplitudes, indicating that the electrical nanotubes network consists of weakly bonded carbon nanotube clusters which can be easily released and reformed. These data also show that MWCNT-MWCNT bonds can be reversibly deformed up to a maximum deformation. The latter experimental result precises the current understanding of electrical carbon nanotubes networks.