Nanoindentation on hybrid organic/inorganic silica aerogels

The hybrid organic/inorganic silica aerogels experiment a drastic mechanical change into rubber behaviour in relation with the pure inorganic silica aerogel as a brittle material. Aerogels were prepared by sol-gel process and drying by venting off the supercritical ethanol, no degradation of the organic polymer was detected. TEOS (tetraethoxysiloxane) and PDMS (polydimethylsiloxane) were used as inorganic and organic precursors, respectively. Depth sensing nanoindentator was used to study the mechanical properties, which is extremely sensitive to small loads (1 mN) and penetration depths (10nm). The TEOS inorganic clusters and the polymer crosslinking degree influence the microstructure of the hybrid aerogels. Surface indentations maps reveal the different heterogeneities such as the tough silica matrix, the softness of the elastic polymer chains and the plastic microcracks in pores. The values obtained are compatible with the macroscopic ones resulting from uniaxial compression. Creep tests confirm that the compliance parameter increases with the polymer content and results can be theoretically modeled by the Burger model. (c) 2007 Elsevier Ltd. All rights reserved.