生物谷：我们知道，鸟类的骨骼和树木的树干结构都经过了长期的自然进化，才达到强度和密度的完美平衡。但是在最新一期Nature Materials上，美国Sandia国家实验室、新墨西哥大学（UNM）和华盛顿天主教大学与普林斯顿大学的科学家们发表文章，声称按人为控制的模式自组装的纳米材料能够超过大自然的杰作。
在更加多孔的同时，又不会过于降低强度。
进行该项研究的是美国Sandia国家实验室、新墨西哥大学、凯斯西储大学以及普林斯顿大学的科学家。项目负责人 Jeffrey Brinker表示，：“微电子学和膜技术领域往往需要既多孔又坚固的材料，通过自组装我们能够在比自然界中更精细的尺度构建硅土材料。在非常小的尺度改变材料的结构和机械性能，才有可能制作出微电子学和膜技术所需要的高硬度、多孔的材料。而新的研究成果使这一切成为可能。”
所谓自组装，一般是指原子、分子或纳米材料通过非共价键作用，在衬底上自发地排列成一维、二维甚至三维的稳定有序的空间结构。研究人员通过核磁共振、拉曼分光研究发现，人工方法使硅薄膜结构更加多孔的同时也会使孔壁厚度变得更薄（不到2纳米），重新排列后的硅结构也会变得更加紧密和坚固。
此前有研究证实，自然界最优化的骨骼的强度会按照密度平方的比例发生变化，而最新的研究表明，自组装纳米材料孔性的增加对劲度模量（stiffness modulus）的影响更小。尤其当纳米材料的孔是立方体结构时，劲度模量会随着自身密度的平方根变化。
Brinker表示，“我们的研究证实，纳米材料孔的结构和大小都会对它的劲度模量产生影响。其中，立方体结构比六边形结构坚固，而六边形结构又比圆柱状结构坚固。对同一种结构而言，孔性增加会导致劲度模量减小，但是减小程度要优于自然进化材料。”
这项研究表明模仿骨头气泡结构的硅土材料纳米结构在气泡体积增加时可能会带来更佳的性能。这将导致许多应用，比如膜栅栏、分子识别传感器、低介电常数绝缘体等下一代微电子设备需要的技术。
原文链接：http://www.physorg.com/news103297694.html
原始出处:
Nature Materials 6, 418 - 423 (2007)
Published online: 21 May 2007 | doi:10.1038/nmat1913
Subject Categories: Nanoscale materials | Porous materials
Modulus–density scaling behaviour and framework architecture of nanoporous self-assembled silicas
Hongyou Fan1,2, Christopher Hartshorn2, Thomas Buchheit1, David Tallant1, Roger Assink1, Regina Simpson1, Dave J. Kissel2, Daniel J. Lacks3, Salvatore Torquato4 & C. Jeffrey Brinker1,2
Natural porous materials such as bone, wood and pith evolved to maximize modulus for a given density1. For these three-dimensional cellular solids, modulus scales quadratically with relative density2, 3. But can nanostructuring improve on Nature's designs? Here, we report modulus–density scaling relationships for cubic (C), hexagonal (H) and worm-like disordered (D) nanoporous silicas prepared by surfactant-directed self-assembly. Over the relative density range, 0.5 to 0.65, Young's modulus scales as (density)n where n(C)<n(H)<n(D)<2, indicating that nanostructured porous silicas exhibit a structure-specific hierarchy of modulus values D<H<C. Scaling exponents less than 2 emphasize that the moduli are less sensitive to porosity than those of natural cellular solids, which possess extremal moduli based on linear elasticity theory4. Using molecular modelling and Raman and NMR spectroscopy, we show that uniform nanoscale confinement causes the silica framework of self-assembled silica to contain a higher portion of small, stiff rings than found in other forms of amorphous silica. The nanostructure-specific hierarchy and systematic increase in framework modulus we observe, when decreasing the silica framework thickness below 2 nm, provides a new ability to maximize mechanical properties at a given density needed for nanoporous materials integration5.
Sandia National Laboratories, Advanced Materials Laboratory, 1001 University Blvd SE, Albuquerque, New Mexico 87106, USA
The University of New Mexico/NSF Center for Micro-Engineered Materials and Department of Chemical and Nuclear Engineering, Albuquerque, New Mexico 87131, USA
Case Western Reserve University, Department of Chemical Engineering, Cleveland, Ohio 44106, USA
Princeton University, Department of Chemistry and Princeton Institute for the Science and Technology of Materials, Princeton, New Jersey 08544, USA
Correspondence to: C. Jeffrey Brinker1,2 e-mail: cjbrink@sandia.gov
