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Isocyanate Cross-Linked Silica: Structurally Strong AerogelsMolecular-level synergism between the silica nanoparticles of pre-formed monoliths and molecular cross-linkers inverts the relative host-guest roles in glass-polymer composites, leading to new strong low-density materials. Attempts to load gels with variable amounts of polyurethane precursors such as di-ISO and diol end-capped polybutylene adipate followed by heat treatment, washing, and supercritical drying led to opaque materials, somewhat stronger than silica but still quite brittle and much inferior to the materials described above. Direct mixing of a diisocyanate and an alcohol-free sol has been attempted recently by Yim et al. Reportedly, that procedure leads to week-long gelation times and requires an at least equally long aging period. In our attempt to add various amounts of di-ISO in a base-catalyzed sol in PC, we also noticed a week-long gelation time. The resulting aerogels were translucent but no less brittle than native silica. According to more recent studies, if propylene carbonate is replaced with acetone, it leads not only to shorter processing times, but also to much stronger gels that can tolerate loads in excess of 40 kg in the arrangement presented. We attribute that behavior to the lower viscosity of acetone, that allows faster diffusion of the di-ISO solution within the pores before di-ISO has time to react with the surface of silica. Further studies are underway to vary the chemical identity of the diisocyanate, as well as the composition and density of silica.
Document ID
20030022658
Acquisition Source
Glenn Research Center
Document Type
Preprint (Draft being sent to journal)
Authors
Leventis, Nicholas (Missouri Univ. Rolla, MO, United States)
Sotiriou-Leventis, Chariklia (Missouri Univ. Rolla, MO, United States)
Zhang, Guo-Hui (Missouri Univ. Rolla, MO, United States)
Rawashdeh, Abdel-Monem M. (Missouri Univ. Rolla, MO, United States)
Date Acquired
August 21, 2013
Publication Date
January 1, 2002
Subject Category
Composite Materials
Meeting Information
Meeting: 225th National American Chemical Society Meeting
Location: New Orleans, LA
Country: United States
Start Date: March 23, 2003
End Date: March 27, 2003
Sponsors: American Chemical Society
Funding Number(s)
PROJECT: RTOP 708-93-06
WBS: WBS 22-708-92-05
CONTRACT_GRANT: ACS-35154-AC5
Distribution Limits
Public
Copyright
Public Use Permitted.

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