| Abstract
| - We describe a new mechanically strong lightweight porous composite material obtained by encapsulatingthe skeletal framework of amine-modified silica aerogels with polyurea. The conformal polymer coatingpreserves the mesoporous structure of the underlying silica framework and the thermal conductivity remainslow at 0.041 ± 0.001 W m-1 K-1. The potential of the new cross-linked silica aerogels for load-carryingapplications was determined through characterization of their mechanical behavior under compression,three-point bending, and dynamic mechanical analysis (DMA). A primary glass transition temperatureof 130 °C was identified through DMA. At room temperature, results indicate a hyperfoam behaviorwhere in compression cross-linked aerogels are linearly elastic under small strains (<4%) and then exhibityield behavior (until 40% strain), followed by densification and inelastic hardening. At room temperaturethe compressive Young's modulus and the Poisson's ratio were determined to be 129 ± 8 MPa and 0.18,respectively, while the strain at ultimate failure is 77% and the average specific compressive stress atultimate failure is 3.89 × 105 N m kg-1. The specific flexural strength is 2.16 × 104 N m kg-1. Effectson the compressive behavior of strain rate and low temperature were also evaluated.
- Amine-modified silica aerogels are cross-linked with interparticle tethers of polyurea. The composite retains the mesoporosity of the native aerogel but it is a very strong material. Its thermal conductivity is 41 mW/mK (≈glass wool), its elastic modulus 129 ± 8 Mpa, and its ultimate specific compressive strength 3.89 × 105 Nm/kg, which is greater than that of Kevlar-49/Epoxy composite.
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