Alexis Liam, Lee Jaejun, Alvarez Gustavo A, Awale Samer, Jesus Diana Santiago-de, Lizcano Maricela, Tian Zhiting
Cornell University Sibley School of Mechanical and Aerospace Engineering, Cornell University, Ithaca New York 14853, United States.
Cornell University Department of Materials Science and Engineering, Cornell University, Ithaca New York 14853, United States.
ACS Appl Mater Interfaces. 2024 Jun 5;16(22):29042-29048. doi: 10.1021/acsami.4c03818. Epub 2024 May 22.
High-temperature polymers are attractive for applications in extreme temperatures, where they maintain their mechanical flexibility and electrical insulating properties. However, their heat dissipation capability is limited due to their intrinsically low thermal conductivities. Hexagonal boron nitride (hBN) is a chemically inert, thermally stable, and electrically insulative compound with a high thermal conductivity, making it an ideal candidate as a filler within a high-temperature polymer matrix to increase the thermal conductivity. This study evaluates the effect of filler size and dispersion on thermal conductivity by producing homogeneous composite samples using a combination of solvent mixing and resonant acoustic mixing (RAM). We carefully characterized our samples, including the spread of the size distribution, and observed that the smaller sized hBN centered around 5 μm was able to integrate more seamlessly into the polytetrafluoroethylene (PTFE) matrix with particle size in the 15 μm range and hence outperformed 30 μm, in contrast to the conventional wisdom, which asserts that larger fillers universally perform better than smaller ones. Our thermal conductivity of hBN/PTFE composites at 30 wt % is 2× higher than the literature values. Notably, we reached the record-high value of 3.5 W/m K at 40 wt % with an onset of percolation at 20 wt %, attributed to optimized hBN dispersion that facilitates the formation of thermal percolation. Our findings provide general guidelines to enhance the thermal conductivity of polymer composites for thermal management, ranging from power transmission to microelectronics cooling.
高温聚合物在极端温度应用中具有吸引力，因为它们能保持机械柔韧性和电绝缘性能。然而，由于其固有的低导热率，它们的散热能力有限。六方氮化硼（hBN）是一种化学惰性、热稳定且电绝缘的化合物，具有高导热率，这使其成为高温聚合物基体中用于提高导热率的理想填料候选物。本研究通过结合溶剂混合和谐振声学混合（RAM）制备均匀的复合样品，评估填料尺寸和分散对导热率的影响。我们仔细表征了我们的样品，包括尺寸分布的范围，并观察到以5μm为中心的较小尺寸hBN能够更无缝地融入粒径在15μm范围内的聚四氟乙烯（PTFE）基体中，因此其性能优于30μm的hBN，这与传统观点相反，传统观点认为较大的填料普遍比较小的填料性能更好。我们制备的30 wt%的hBN/PTFE复合材料的导热率比文献值高2倍。值得注意的是，我们在40 wt%时达到了3.5 W/m K的创纪录高值，在20 wt%时开始出现渗流，这归因于优化的hBN分散，有利于形成热渗流。我们的研究结果为提高用于热管理的聚合物复合材料的导热率提供了一般指导方针，涵盖从电力传输到微电子冷却等领域。
