金属纳米线气凝胶中的热扩散率

中文摘要 AI 辅助

金属纳米线气凝胶兼具金属的功能特性与气凝胶的高孔隙率。本文通过冷冻铸造法合成了密度为20-500 mg cm-3的银（Ag）和铜（Cu）纳米线气凝胶，并在顺序机械压实过程中使用锁相热成像技术对其进行了研究。热传输强烈依赖于纳米线直径：30 nm银纳米线的热扩散率显著低于60 nm纳米线，这可能是由于当线径接近银中电子平均自由程时，表面散射增强所致。令人惊讶的是，通过机械压实提高气凝胶密度使计算得到的热扩散率降低了近300倍，这与密度更大的材料更高效传导热量的传统预期相反。进一步分析表明，这种降低主要由热扩散率公式中的厚度项主导，而拟合的传输系数变化相对较小。特征热扩散时间尺度在压实过程中仅适度减小，表明致密化主要压缩孔隙体积，而并未从根本上重构导电纳米线网络。这种行为类似于保持拓扑的致密化，其中大的几何压缩产生相对较小的有效渗流传输路径变化。这些结果表明，纳米线气凝胶不能总是被视为均匀的块体材料，因为其宏观几何形状和导电网络在压实过程中以不同方式演化。

英文摘要

Metallic nanowire aerogels combine the functional properties of metals with the high porosity of aerogels. Here, Ag and Cu nanowire aerogels with densities of 20-500 mg cm-3 were synthesized by freeze casting and investigated using lock-in thermography during sequential mechanical compaction. Thermal transport depended strongly on nanowire diameter, with 30 nm Ag nanowires exhibiting substantially lower thermal diffusivity than 60 nm wires, likely due to enhanced surface scattering as the wire diameter approaches the electron mean free path in Ag. Surprisingly, increasing the aerogel density through mechanical compaction reduced the calculated thermal diffusivity by nearly 300x, opposite the conventional expectation that denser materials transport heat more efficiently. Further analysis showed that this decrease is dominated by the thickness term in the thermal diffusivity formalism, while the fitted transport coefficient changes comparatively little. The characteristic thermal diffusion timescale decreased only modestly during compaction, indicating that densification primarily collapses pore volume without fundamentally restructuring the conductive nanowire network. This behavior resembles topology-preserving densification, where large geometric compression produces comparatively small changes in the effective percolative transport pathway. These results show that nanowire aerogels cannot always be treated as homogeneous bulk media, because their macroscopic geometry and conductive network evolve differently during compaction.

发表机构

• University of Tennessee（田纳西大学）
• Georgetown University（乔治城大学）

机构由 AI 辅助整理，请以论文原文为准。