The Role of the Surface Roughness and Filler Size on Performance of Graphene-Based Thermal Interface Materials
In the first part of this thesis, I present the results of my investigation of thermal characteristics of the silicone-oil based thermal interface materials (TIMs) with randomly oriented graphene and few-layer graphene fillers. The graphene TIMs were applied between surfaces with different degrees of roughness. It was found that the thermal contact resistance depends on the graphene loading, ξ, non-monotonically, achieving its minimum at the loading fraction of ξ~ 15 wt.%. Decreasing the surface roughness by ~1 μm results in approximately the factor of ×2 decrease in the thermal contact resistance for this graphene loading. The obtained dependences of the thermal conductivity, thermal contact resistance, and the total thermal resistance of the thermal interface material layer on the loading fraction and roughness can be utilized for optimization of graphene TIMs for specific materials and roughness of the connecting surfaces. In the second part of the thesis, I evaluate the performance of graphene TIMs with different filler sizes. It was established that with increase in the size of the fillers, the thermal conductivity of silicone-oil based TIMs increases. The experimentally obtained values of the thermal conductivity were fitted with the theoretical model. It was also found that the thermal contact resistance (TCR) of the TIMs decreases with increasing filler size. The obtained results are important for development of non-cured TIMs for applications in thermal management of high-power density electronics.