Evolution of agglomerate structure of carbon nanotubes in multi-walled carbon nanotubes/polymer composite melt: A rheo-electrical study

Agglomerate structure of nano-fillers in polymer composite definitely plays a key role in the functionalization of nanocomposite. As nano-fillers are prone to agglomerating, the agglomerate structure is unstable and will experience a remarkable evolution in the melt state of the composite. In this work, the influence of melt annealing on the microstructure of multi-walled carbon nanotubes/poly(vinylidene fluoride) composites has been investigated by a combination of rheological behavior and electrical properties. The simultaneous measurement, which is combined with investigations of rheological behavior and resistance, reveals that the evolution of microstructures during melt annealing shows a significant effect on both the viscoelasticity and electrical conductivity of composites. Besides, a watershed behavior is found for the evolution of microstructure in samples with the content of MWCNTs higher and lower than the electrical percolation threshold (φC) during annealing. Particularly, samples with the content of MWCNTs above φC exhibit a noteworthy increment in storage modulus and a dramatic decrease in resistance, while those with the content of MWCNTs below φC display a quick decrease in electrical conductivity and only a slight increment in storage modulus.