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UBC Theses and Dissertations

Computationally efficient modeling and analysis of conductivity and sensitivity of CNT/polymer composites Rahman, Rubaiya


In this PhD thesis, an efficient model of conductivity for carbon nanotube (CNT)/polymer composites is developed, considering the effect of intertube tunneling through polymers, and the eletromechanical properties of the composites are estimated. The statistical nature of intertube distance is first investigated through numerical analysis for both two dimensional and three dimensional networks of CNTs. Considering the intertube distance as the key parameter of tunneling effect, analytical models are developed for tunneling conductivity at the CNT junctions and the overall conductivity of the composites. The model of composite conductivity provides significantly lower computational cost as compared to the numerical resistive network models, with reasonable accuracy. By incorporation of electron tunneling effects, this model also provides closer approximation to experimental results in comparison to the models based on percolation theory, which are highly relevant for filler/polymer composite applications designed around the percolation threshold. Using the conductivity model, the sensitivity of the composite films is estimated in presence of an organic gas. The change in the film resistance due to gas absorption is investigated for different CNT and gas concentrations. From the phase of reflected radio frequency (RF) signal, the wireless gas sensitivity is estimated for a lossless transmission system terminated with a composite film as the load. Films with lower filler concentration is found to have higher gas sensitivity and higher wireless sensitivity within a low range of gas pressure. This work is useful for design and development of biohazard gas sensors for real-time remote monitoring. Furthermore, the sensitivity of the composite films is estimated under the application of tensile strain. The influence of varying film thickness on the intertube distance in composite films is analyzed numerically. Then our analytical model is employed to estimate the composite conductivity and film sensitivity under mechanical strain. The partial alignment of CNTs introduced by the film thickness less than the CNT length is observed to have significant influence on the composite conductivity and strain sensitivity specially at low CNT concentration. The numerical results are compared with literature reports and experimental results. This work is helpful for strain sensing and stretchable switching applications.

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