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.

In this dissertation, the methods for preparation and experimental testing of polymer-based composites with fillers comprised of quasi-one-dimensional charge-density-wave (CDW) material – Niobium Trisulfide (NbS3) are presented. Owing to the crystal growth conditions, the NbS3 crystals appear as a mixture of various polymorphs. Among these polymorphs, only the NbS3-II polymorph reveals the charge density wave (CDW) characteristics. Prior to composite preparation, the synthesized crystals were characterized with the metrology techniques of transmission electron microscopy (TEM) to determine their crystal structure and studied with Raman spectroscopy as a function of temperature to observe the CDW property. The use of CDW van der Waals materials, as fillers, is expected to provide novel functionalities to the composites if one develops preparation techniques that preserve the intrinsic properties of the fillers. This task is challenging because composite preparation involves mechanical mixing, centrifugation, and other processing steps that typically result in damage and high concentrations of defects and impurities. The process of the composite preparation starts with liquid phase exfoliation to acquire fillers. The tested polymer materials included epoxy resin, UV-cured epoxy resin, and Polyvinylidene fluoride (PVDF). The composites have been characterized using differential scanning calorimetry, Raman spectroscopy, ellipsometry, optical microscopy, and parallel-plate capacitance measurements. The electrical capacitance measurements of PVDF thin films with NbS3 fillers demonstrated a significant change in the dielectric constant at the temperature near the CDW transition. The results of this dissertation research prove that temperature-dependent Raman spectroscopy can be used as an efficient characterization technique to distinguish NbS3-II polymorph with CDW properties from other NbS3 phases and add to the development of methods for the preparation of composites with the quasi-1D van der Waals materials.