Enhancing Polymer Composite Thermal Conductivity by Liquid Metal and Carbon Fiber Dual Fillers

Polymers, including poly(vinylidene fluoride) (PVDF), have been widely used in daily life and industries, such as in membrane filtration, food packing and heat exchanging. However, pristine polymers suffer from inherently low thermal conductivity. Herein, thermally conductive poly(vinylidene fluoride) (PVDF) composites were prepared by incorporating eutectic gallium–indium (EGaIn) liquid metals (LMs) and carbon fibers (CFs) as dual fillers. The effects of the LMs and the CFs on the thermal and mechanical properties of the PVDF composites were characterized via thermal conductivity, morphology, crystallinity, and mechanical testing. The CFs improved the dispersion of the LM droplets within the PVDF matrix, forming continuous thermally conductive pathways, thereby enhancing the composite thermal conductivity. A maximum thermal conductivity of 0.40 W/(m·K), an increase of 154% over the pure PVDF, was achieved when 1 wt% CF was added to the PVDF composites containing 5 wt% LMs. Mechanical testing showed that the CFs compensated for the slight reduction in tensile strength due to the LM addition, yielding a tensile strength of 30 ± 3 MPa, slightly higher than that of the pure PVDF. Characterization analyses confirmed that the crystalline and chemical structure of the PVDF matrix were preserved after the filler addition, indicating minimal alteration of the PVDF matrix. These results suggest that the PVDF/LM/CF composites exhibit a balanced enhancement of the thermal conductivity and mechanical strength, making them potential candidates for thermal management applications. This study provides insights into designing high-performance polymer composites with dual functionality for advanced engineering applications.