Nanocarbon based polymer composites (PNCs) are attractive structural materials with superior multifunctionalty arising from the remarkable properties of the nanocarbons themselves and scaling effects. However, the measured properties of the PNCs fall short of their predicted values, owing to poorly understood structure-interphase-property relationships. In this presentation, a powerful method combining electron tomography and stochastic simulations is demonstrated as being effective in defining nanocomposite structure-property relations, identifying it as a key step towards understanding and tailoring the next-generation of advanced composites. Firstly, we describe an electron tomography technique for the nanoscale characterization of high volume fraction aligned carbon nanotube composites. The information rich, 3D data is quantified using image analysis to obtained morphological metrics such as volume fraction, tortuosity, alignment quality, junction density, etc.  A framework to convert the measured 3D tortuosity to waviness is developed and used to define a novel form of waviness that incorporates the stochastic nature of CNT growth. The importance of modeling CNTs as randomly wavy objects is validated by the now remarkable agreement between simulated and previously-measured PNC elastic moduli. The statistical view of aligned-CNT structures developed here is also substantiated by agreements between simulated and experimentally measured secondary morphological descriptors such as CNT-CNT junction density and inter-junction distances. The scaling of the junction density with CNT volume fraction is observed for the first time to be non-linear and consistent with the scaling predictions for diffusion-limited networks of semi-dilute elongated macromolecules. This supports the treatment of nanotubes as rigid-rod polymers. This non-linearity explains the non-linear scaling of aligned-CNT PNC longitudinal thermal conductivity. In contrast, the measured electrical conductivity scales linearly with volume fraction and is relatively insensitive to junction density beyond percolation. This result confirms the hypotheses that the conduction in such fully percolated and continuous CNT composites is dominated by the bulk resistivity of the components.<br/>

Structure property relationships in high volume fraction carbon nanotube composites

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.