Modulation of Interfacial Thermal Transport between Fumed Silica Nanoparticles by Surface Chemical Functionalization for Advanced Thermal Insulation
Modulation of Interfacial Thermal Transport between Fumed Silica Nanoparticles by Surface Chemical Functionalization for Advanced Thermal Insulation
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DOI：
10.1021/acsami.0c11066
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发表时间：
2021-04-12
影响因子：
9.5
通讯作者：
Shiomi, Junichiro
中科院分区：
文献类型：
--
作者：
Kodama, Takashi;Shinohara, Nobuhiro;Shiomi, Junichiro
由于高多孔纳米复合材料中的固态热传递强烈依赖于组成纳米材料之间的热边界导率（TBC），因此进一步抑制TBC对于提高隔热材料的性能非常重要。本文以冲压成型的气相二氧化硅纳米颗粒为目标，通过硅烷偶联方法对气相二氧化硅纳米颗粒进行了多种表面功能化，并研究了其对导热系数（K-m）的影响。在大气和真空条件下，材料密度为0.2 g/cm(3)，无表面功能化时，二氧化硅纳米复合材料的K-m分别约为20和9 mW/m/K，实验结果表明，K-m可以根据分子的化学结构进行调节。采用最佳长度的线性烷基链进行表面改性可显著抑制K-m约30%，红外不透明剂可进一步将抑制率提高至约50%。抑制的大小被发现敏感地依赖于末端链的长度。其大小还与化学结构中反应性硅烷醇基团的数量有关，其中氟碳表面改性的抑制作用最大。通过显著抑制TBC，表面疏水作用有利于隔热，这可能是通过减少水分子来实现的，否则水分子将在界面处充当热传导通道。另一方面，当链长较长时，通过随链长增长的硅烷偶联分子增强声子传输会抵消这种抑制。分析模型和目前的模拟结果支持了这一点，从而预测了最佳的化学结构，以获得更好的隔热效果。
Since solid-state heat transport in a highly porous nanocomposite strongly depends on the thermal boundary conductance (TBC) between constituent nanomaterials, further suppression of the TBC is important for improving performance of thermal insulators. Here, targeting a nanocomposite fabricated by stamping fumed silica nanoparticles, we perform a wide variety of surface functionalizations on fumed silica nanoparticles by a silane coupling method and investigate the impact on the thermal conductivity (K-m). The K-m of the silica nanocomposite is approximately 20 and 9 mW/m/K under atmospheric and vacuum conditions at the material density of 0.2 g/cm(3) without surface functionalization, respectively, and the experimental results indicate that the K-m can be modulated depending on the chemical structure of molecules. The surface modification with a linear alkyl chain of optimal length significantly suppresses K-m by approximately 30%, and the suppression can be further enhanced to approximately 50% with an infrared opacifier. The magnitude of suppression was found to sensitively depend on the length of the terminal chain. The magnitude is also related to the number of reactive silanol groups in the chemical structure, where the surface modification with fluorocarbon gives the largest suppression. The surface hydrophobization merits thermal insulation through significant suppression of the TBC, presumably by reducing the water molecules that otherwise would serve as heat conduction channels at the interface. On the other hand, when the chain length is long, the suppression is counteracted by the enhanced phonon transmission through the silane coupling molecules that grow with the chain length. This is supported by the analytical model and present simulation results, leading to prediction of the optimal chemical structure for better thermal insulation.