Letter abstract
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
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