title: Modulus-density scaling behaviour and framework architecture of nanoporous self-assembled silicas.
abstract: Natural porous materials such as bone, wood and pith evolved to maximize modulus for a given density. For these three-dimensional cellular solids, modulus scales quadratically with relative density. 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 theory. 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 integration.
authors.affiliation: Sandia National Laboratories, Advanced Materials Laboratory, 1001 University Blvd SE, Albuquerque, NM 87106, USA.
authors.forename: Hongyou
authors.initials: H
authors.lastname: Fan
authors.forename: Christopher
authors.initials: C
authors.lastname: Hartshorn
authors.forename: Thomas
authors.initials: T
authors.lastname: Buchheit
authors.forename: David
authors.initials: D
authors.lastname: Tallant
authors.forename: Roger
authors.initials: R
authors.lastname: Assink
authors.forename: Regina
authors.initials: R
authors.lastname: Simpson
authors.forename: Dave J
authors.initials: DJ
authors.lastname: Kissel
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Lacks
authors.forename: Salvatore
authors.initials: S
authors.lastname: Torquato
authors.forename: C Jeffrey
authors.initials: CJ
authors.lastname: Brinker
mesh_terms: D000327:Adsorption; D004548:Elasticity; D009682:Magnetic Resonance Spectroscopy; D008422:Materials Testing; D046529:Microscopy, Electron, Transmission; D053758:Nanoparticles; D049329:Nanostructures / Q000737:chemistry*; D036103:Nanotechnology / Q000379:methods*; D016062:Porosity; D012822:Silicon Dioxide / Q000737:chemistry*; D013059:Spectrum Analysis, Raman / Q000379:methods; D013501:Surface-Active Agents / Q000737:chemistry
chemical_list: D013501:Surface-Active Agents; D012822:Silicon Dioxide