生物谷：我們知道,，鳥類的骨骼和樹木的樹干結構都經(jīng)過了長期的自然進化,，才達到強度和密度的完美平衡,。但是在最新一期Nature Materials上,，美國Sandia國家實驗室,、新墨西哥大學（UNM）和華盛頓天主教大學與普林斯頓大學的科學家們發(fā)表文章,，聲稱按人為控制的模式自組裝的納米材料能夠超過大自然的杰作,。
在更加多孔的同時，又不會過于降低強度,。
進行該項研究的是美國Sandia國家實驗室,、新墨西哥大學、凱斯西儲大學以及普林斯頓大學的科學家,。項目負責人 Jeffrey Brinker表示,，：“微電子學和膜技術領域往往需要既多孔又堅固的材料，通過自組裝我們能夠在比自然界中更精細的尺度構建硅土材料,。在非常小的尺度改變材料的結構和機械性能,，才有可能制作出微電子學和膜技術所需要的高硬度、多孔的材料,。而新的研究成果使這一切成為可能,。”
所謂自組裝，一般是指原子,、分子或納米材料通過非共價鍵作用,，在襯底上自發(fā)地排列成一維、二維甚至三維的穩(wěn)定有序的空間結構,。研究人員通過核磁共振,、拉曼分光研究發(fā)現(xiàn),，人工方法使硅薄膜結構更加多孔的同時也會使孔壁厚度變得更薄（不到2納米）,，重新排列后的硅結構也會變得更加緊密和堅固,。
此前有研究證實，自然界最優(yōu)化的骨骼的強度會按照密度平方的比例發(fā)生變化,，而最新的研究表明,，自組裝納米材料孔性的增加對勁度模量（stiffness modulus）的影響更小。尤其當納米材料的孔是立方體結構時,，勁度模量會隨著自身密度的平方根變化,。
Brinker表示，“我們的研究證實,，納米材料孔的結構和大小都會對它的勁度模量產(chǎn)生影響,。其中，立方體結構比六邊形結構堅固,，而六邊形結構又比圓柱狀結構堅固,。對同一種結構而言，孔性增加會導致勁度模量減小,，但是減小程度要優(yōu)于自然進化材料,。”
這項研究表明模仿骨頭氣泡結構的硅土材料納米結構在氣泡體積增加時可能會帶來更佳的性能。這將導致許多應用,，比如膜柵欄,、分子識別傳感器、低介電常數(shù)絕緣體等下一代微電子設備需要的技術,。
原文鏈接：http://www.physorg.com/news103297694.html
原始出處:
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: [email protected]
