A Study on Thermal Conductivity Enhancement in Composites Utilizing Excluded Volume Effects.

Loading highly thermally conductive fillers, such as graphene nanoplatelets, into low-conductivity matrices (e.g., polymers) allows significant thermal conductivity improvements required in various thermal management applications. At high loadings, percolation enhances this effect due to the formation of conductive pathways. In the excluded volume approach, one adds high-volume fillers to increase the effective concentration of the thermally conductive fillers, potentially lowering their percolation threshold and facilitating filler interactions at lower loadings. The present study aims to investigate this notion and examine conditions at which this phenomenon occurs. A two-dimensional numerical analysis is devised, focusing initially on a thermally inert high-volume filler, which allows isolating its effects on compacting the highly conductive fillers. The analysis reveals that relatively high loadings of the highly conductive filler, namely over 20% in volume, are required to achieve significant enhancements. Comparing the modeling with experimental results indicates a good correlation, predicting enhancements of up to 20% due to the addition of the high-volume filler. These findings highlight the potential for optimizing composite conductivity through controlled filler addition by utilizing the excluded volume effect.