On the effective thermal conductivity of carbon nanotube reinforced polymer composites

The focus of the present thesis is to develop a fundamental understanding of the heat conduction process in carbon nanotube reinforced polymer composites and to elucidate the contribution of the various factors which affect it at the nanometer level. To this end, a theoretical model has been developed for predicting the effective longitudinal thermal conductivity of an aligned multi-walled nanotube/polymer composite. This model is based on an effective medium theory that has been developed for predicting the thermal conductivity of short fiber composites. To incorporate the multi-walled nanotube structure into this theory, a continuum model of the nanotube geometry is developed by considering its structure and the mechanism of heat conduction through it. Results show that the effective conductivity will be much lower than expected due to the fact that the outer nanotube layer carries the bulk of the heat flowing through the nanotube while the contribution of the inner layers to heat flow is negligible. Also, the effective conductivity has been found to be particularly sensitive to the multi-walled nanotube diameter. In addition, it has been found that the high interfacial resistance between the nanotube and polymer matrix is not the principal factor which affects the flow of heat in carbon nanotube composites. Theoretical predictions are found to be very close to published experimental results.