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Strain-dependent Optical and Thermal Properties of CNT films


Passive surface thermal regulation is an area of critical interest, with many potential applications ranging from the design of energy efficient building coatings to applications such as thermo camouflage. The thermoregulation of a surface requires the dynamic modulation of emissivity and reflectivity of the material; these changes are achieved via the manipulation of the surface morphology of the material. The work presented in this thesis used a strain driven CNT film to achieve the said morphology changes. In the experimental characterization of CNT films, a 0.047 increase in the average solar reflectivity was observed when strain up to 80%. When exposed to direct sunlight, this change in reflectivity was manifested as a temperature change of 2.8℃. Following the experimental work, a 3D model was developed to represent the CNT film. The developed model was simulated using raytracing under varying levels of strain, these results were used to develop a hypothesis. The developed hypothesis viewed the surface of the CNT films to be composed of many pit-like structures; the shallowing of the pit depth when strained was determined to be the driving mechanism of increased reflectivity. Later based on the developed hypothesis a simpler periodic model was created to provide an enhanced strain-dependent reflectivity increase of 0.145 in the solar region. This model was further improved by adding a silver backed layer to provide an increased averaged solar reflectivity of 0.6826 resulting in a surface temperature change of nearly 61℃.

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