Centre for Natural Material Innovation, Dept. of Architecture, University of Cambridge, Cambridge, CB2 1PX, UK.
Institute of Wood Technology and Renewable Materials, Department of Material Sciences and Process Engineering, University of Natural Resources and Life Sciences Vienna, Konrad-Lorenz-Strasse 24, 3430, Tulln an der Donau, Austria.
Sci Rep. 2019 Nov 13;9(1):16667. doi: 10.1038/s41598-019-53079-4.
Scanning thermal microscopy is a powerful tool for investigating biological materials and structures like bamboo and its cell walls. Alongside nanoscale topographical information, the technique reveals local variations in thermal conductivity of this elegant natural material. We observe that at the tissue scale, fibre cells in the scattered vascular tissue would offer preferential pathways for heat transport due to their higher conductivities in both anatomical directions, in comparison to parenchymatic cells in ground tissue. In addition, the transverse orientation offers more resistance to heat flow. Furthermore, we observe each fibre cell to compose of up to ten layers, with alternating thick and thin lamellae in the secondary wall. Notably, we find the thin lamellae to have relatively lower conductivity than the thick lamellae in the fibre direction. This is due to the distinct orientation of cellulose microfibrils within the cell wall layers, and that cellulose microfibrils are highly anisotropic and have higher conductivity along their lengths. Microfibrils in the thick lamellae are oriented almost parallel to the fibre cell axis, while microfibrils in the thin lamellae are oriented almost perpendicular to the cell axis. Bamboo grasses have evolved to rapidly deposit this combination of thick and thin layers, like a polymer composite laminate or cross-laminated timber, for combination of axial and transverse stiffness and strength. However, this architecture is found to have interesting implications on thermal transport in bamboo, which is relevant for the application of engineered bamboo in buildings. We further conclude that scanning thermal microscopy may be a useful technique in plant science research, including for phenotyping studies.
扫描热显微镜是一种强大的工具，可用于研究生物材料和结构，如竹子及其细胞壁。除了纳米级形貌信息外，该技术还揭示了这种优雅天然材料热导率的局部变化。我们观察到，在组织尺度上，分散的维管束组织中的纤维细胞由于其在解剖方向上的较高导热率，将为热传输提供优先途径，而与基质组织中的薄壁细胞相比。此外，横向方向对热流的阻力更大。此外，我们观察到每个纤维细胞由多达十个层组成，在次生壁中的厚和薄的片层交替排列。值得注意的是，我们发现薄的片层在纤维方向上的导热率比厚的片层相对较低。这是由于细胞壁层中纤维素微纤维的独特取向，以及纤维素微纤维在其长度上具有高度各向异性和较高的导电性。厚片层中的微纤维几乎与纤维细胞轴平行取向，而薄片层中的微纤维几乎与细胞轴垂直取向。竹子已经进化到能够快速沉积这种厚层和薄层的组合，就像聚合物复合材料层压板或交错层压木材一样，以实现轴向和横向的刚度和强度的结合。然而，这种结构在竹子的热传输中具有有趣的意义，这与工程竹在建筑中的应用有关。我们进一步得出结论，扫描热显微镜可能是植物科学研究中的一种有用技术，包括表型研究。
