The effect of crystalline defects and geometry factors of multi-walled carbon nanotubes on electrical conductivity of silver-nitrile butadiene rubber composites

It is important to construct effective electrical network to achieve high electrical conductivity of soft polymer matrix composites. We previously employed one-dimensional multi-walled carbon nanotubes (MWNTs) decorated with silver nanoparticles (nAg-MWNTs) and micron-sized silver flakes in a nitrile butadiene rubber matrix to develop highly conductive flexible adhesive (CFA) films. However, the effect of intrinsic physical properties of MWNTs on the conductivity of CFA was not explored in detail. Here we investigated the influence of crystalline defects and geometry factors of MWNTs on the electrical conductivity of CFA films. The nAg-MWNTs were synthesized using five different MWNTs. The electrical conductivity of the CFA films decreased significantly with an increase in Raman D- to G-mode ratio demonstrating the crystallinity effect. There was the tube diameter dependence. The conductivity increased as the diameter of MWNTs decreased. The dispersion was also a determining factor. The strongly entangled structure of MWNTs originated from the initial synthesis process caused aggregation of tubes in the polymer matrix resulting in a low conductivity of CFA film. However, the tube length dependence was not obvious in the investigated range (5-20 μm). It was possible that all the tubes were long enough not to differentiate the length effect on percolation. These findings may provide a guideline for selection of MWNTs to achieve high conductivity of flexible composites.