Thermal conduction in graphite flake-epoxy composites using infrared microscopy

Thermally conductive polymer composites, in particular those composed of polymers and carbon-based nanomaterials, are promising for thermal management in electronic devices because they offer high thermal conductivity at low filler loading. The effective thermal properties of these composites exhibit high variability that depend on the topological arrangements and morphological characteristics of the filler particles. In order to tailor the thermal conduction within these composites for use as an efficient heat dissipation material, careful control of the microstructural arrangement of the filler material is required. In this work, we use infrared (IR) microscopy to characterize thermal transport through epoxy composites containing sub-millimeter sized graphitic flakes as filler particles. Graphite flake-epoxy composites of two volume fractions (3%, 25%) are prepared and characterized using an infrared microscope with a temperature resolution of 0.1 K that images the temperature distribution at the top surface of the composite subject to a temperature gradient. The effective thermal conductivity of the composite with a 25% filler fraction was found to be 2.9 W/m-K, a factor of 16 higher than the neat epoxy. With the micron-scale resolution of the IR microscope, the steady-state particle-scale temperature fields within the composite are directly observed and highlight the non-uniform heat transfer pathways. This local temperature analysis reveals the impact of important microstructural features such as clustering of filler particles. Ultimately, this approach could be used to investigate percolation and anisotropic heat conduction in composites with shear aligned particles.