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Understanding Thermal Insulation in Porous, Particulate Materials

机译：了解多孔颗粒材料中的隔热

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摘要

Silica hollow nanosphere colloidal crystals feature a uniquely well-defined structure across multiple length scales. This contribution elucidates the intricate interplay between structure and atmosphere on the effective thermal diffusivity as well as the effective thermal conductivity. Using silica hollow sphere assemblies, one can independently alter the particle geometry, the density, the packing symmetry, and the interparticle bonding strength to fabricate materials with an ultralow thermal conductivity. Whereas the thermal diffusivity decreases with increasing shell thickness, the thermal conductivity behaves inversely. However, the geometry of the colloidal particles is not the only decisive parameter for thermal insulation. By a combination of reduced packing symmetry and interparticle bonding strength, the thermal conductivity is lowered by additionally 70% down to only 8 mW m(-1) K-1 in vacuum. The contribution of gaseous transport, even in these tiny pores (<200 nm), leads to minimum thermal conductivities of approximate to 35 and approximate to 45 mW m(-1) K-1 for air and helium atmosphere, respectively. The influence of the individual contributions of the solid and (open- and closed-pore) gaseous conductions is further clarified by using finite element modeling. Consequently, these particulate materials can be considered as a non-flammable and dispersion-processable alternative to commercial polymer foams.
机译：二氧化硅空心纳米球胶体晶体在多个长度尺度上具有独特定义明确的结构。这一贡献阐明了结构与大气之间在有效热扩散率以及有效热导率上的复杂相互作用。使用二氧化硅空心球组件，可以独立地更改粒子的几何形状，密度，堆积对称性和粒子间的结合强度，以制造具有超低导热率的材料。尽管热扩散率随壳体厚度的增加而减小，但热导率却相反。然而，胶体颗粒的几何形状不是绝热的唯一决定性参数。通过减少堆积对称性和颗粒间结合强度的组合，真空中的导热系数又降低了70％，仅为8 mW m（-1）K-1。即使在这些微小的孔（<200 nm）中，气体的输送也会导致空气和氦气的最小热导率分别约为35和45 mW m（-1）K-1。固体和（开孔和闭孔）气体传导的各个贡献的影响通过使用有限元建模进一步阐明。因此，这些颗粒材料可被视为商业聚合物泡沫的不可燃和可分散加工的替代物。

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