Institute for Building Materials (IfB), Wood Materials Science, ETH Zürich , Stefano-Franscini-Platz 3, 8093 Zürich, Switzerland.
ACS Appl Mater Interfaces. 2014 Jun 25;6(12):9760-7. doi: 10.1021/am5021793. Epub 2014 Jun 12.
Anisotropic and hierarchical structures are bound in nature and highly desired in engineered materials, due to their outstanding functions and performance. Mimicking such natural features with synthetic materials and methods has been a highly active area of research in the last decades. Unlike these methods, we use the native biomaterial wood, with its intrinsic anisotropy and hierarchy as a directional scaffold for the incorporation of magnetic nanoparticles inside the wood material. Nanocrystalline iron oxide particles were synthesized in situ via coprecipitation of ferric and ferrous ions within the interconnected pore network of bulk wood. Imaging with low-vacuum and cryogenic electron microscopy as well as spectral Raman mapping revealed layered nanosize particles firmly attached to the inner surface of the wood cell walls. The mineralogy of iron oxide was identified by XRD powder diffraction and Raman spectroscopy as a mixture of the spinel phases magnetite and maghemite. The intrinsic structural architecture of native wood entails a three-dimensional assembly of the colloidal iron oxide which results in direction-dependent magnetic features of the wood-mineral hybrid material. This superinduced magnetic anisotropy, as quantified by direction-dependent magnetic hysteresis loops and low-field susceptibility tensors, allows for directional lift, drag, alignment, (re)orientation, and actuation, and opens up novel applications of the natural resource wood.
各向异性和分层结构在自然界中是固有的，在工程材料中也备受青睐，因为它们具有出色的功能和性能。在过去几十年中，用合成材料和方法模拟这些自然特征一直是一个非常活跃的研究领域。与这些方法不同，我们使用天然生物材料木材，其各向异性和分层结构作为内在的定向支架，将磁性纳米粒子纳入木材材料中。通过在块状木材的互连孔网络中内共沉淀铁离子和亚铁离子，原位合成了纳米晶氧化铁颗粒。利用低真空和低温电子显微镜成像以及光谱拉曼映射，发现纳米级颗粒牢固地附着在细胞壁的内表面上。通过 X 射线粉末衍射和拉曼光谱鉴定氧化铁的矿物学为尖晶石相磁铁矿和磁赤铁矿的混合物。天然木材的固有结构架构需要胶体氧化铁的三维组装，这导致木材-矿物复合材料具有各向异性的磁特性。这种超感应磁各向异性，如各向异性磁滞回线和低场磁化率张量所定量的，可以实现定向提升、拖拽、对齐、（重新）定向和驱动，为自然资源木材开辟了新的应用。
