Thermal Percolation in Well-Defined Nanocomposite Thin Films
Thermal Percolation in Well-Defined Nanocomposite Thin Films
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DOI：
10.1021/acsami.2c00296
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发表时间：
2022-03-30
影响因子：
9.5
通讯作者：
Xu, Ting
中科院分区：
文献类型：
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作者：
Chang, Boyce S.;Li, Chen;Xu, Ting
聚合物纳米复合材料中的热渗流-由于填料之间形成网络而导致的热传输的快速增加-是热管理领域的热门话题，从多功能纳米复合材料的一般用途到高导电性应用，如热界面材料。然而，它仍然是一个具有挑战性的课题，包括实验和建模障碍。热渗透的成功报道仅在高纵横比的导电填料如石墨烯中发现，尽管填料负载量显著高于电渗透阈值。该异常归因于与类似于10（12）-10（16）的电导率相比，类似于10（4）的较低填料-基质热导率对比率k（f）/km。在随机分散的复合材料中，低对比度的影响进一步加剧的不确定性，在形态的分散网络和存在的其他相，如断开的聚集体和胶体分散体。因此，网络的一般属性是复杂的，因为它们缺乏定义的结构。相比之下，具有可控纳米填料放置的原型系统能够阐明结构-性质关系，例如填料尺寸、负载和组装。使用自组装的纳米复合材料与控制的1，2，3维纳米粒子（NP）的安排，我们证明，尽管使用球形，非导电填料（k（f）/k（m）类似于60）在低体积分数（9体积%），可以实现热渗流。我们观察到的体积分数，界面热阻，和填料的导热系数的导热系数的影响离开有效介质近似。最值得注意的是，对比度在高于k（f）/k（m）的热渗透中起次要作用，类似于60-半导体纳米颗粒/聚合物比率的常见范围。我们的研究结果带来了新的观点和见解，在纳米复合材料中，在对比度，界面热导率和填料尺寸的限制。
Thermal percolation in polymer nanocomposites-the rapid increase in thermal transport due to the formation of networks among fillers-is the subject of great interest in thermal management ranging from general utility in multifunctional nanocomposites to high-conductivity applications such as thermal interface materials. However, It remains a challenging subject encompassing both experimental and modeling hurdles. Successful reports of thermal percolation are exclusively found in high-aspect-ratio, conductive fillers such as graphene, albeit at filler loadings significantly higher than the electrical percolation threshold. This anomaly was attributed to the lower filler-matrix thermal conductivity contrast ratio k(f)/km similar to 10(4) compared to electrical conductivity similar to 10(12)-10(16). In a randomly dispersed composite, the _ effect of a low contrast ratio is further accentuated by uncertainties in the morphology of the percolating network and presence of other phases such as disconnected aggregates and colloidal dispersions. Thus, the general properties of percolating networks are convoluted as they lack a defined structure. In contrast, a prototypical system with controllable nanofiller placement enables the elucidation of structure-property relations such as filler size, loading, and assembly. Using self-assembled nanocomposites with a controlled 1,2,3-dimension nanoparticle (NP) arrangement, we demonstrate that thermal percolation can be achieved in spite of using spherical, nonconductive fillers (k(f)/k(m) similar to 60) at a low volume fraction (9 vol %). We observe that the effects of volume fraction, interfacial thermal resistance, and filler conductivity on thermal conductivity depart from effective medium approximations. Most notably, contrast ratio plays a minor role in thermal percolation above k(f) /k(m) similar to 60-a common range for semiconducting nanoparticles/polymer ratios. Our findings bring new perspectives and insights to thermal percolation in nanocomposites, where the limits in contrast ratio, interfacial thermal conductance, and filler size are established.