Mechanical properties of monolithic silica aerogels made from polyethoxydisiloxanes

We report the preparation and characterization of a broad range of hydrophobic monolithic silica aerogels and xerogels made from polyethoxydisiloxane (PEDS-P-750E20) precursors. Transparent silica aerogels with densities spanning approximate to 0.05 to >0.32 g/cm(3) were synthesized and the effects of density on the mechanical, microstructural, and thermal properties were studied. In the samples investigated, the elastic modulus E was found to vary from 40 kPa to 70 MPa, compressive strength sigma(C) from 500 kPa to 4.2 MPa, fracture strain epsilon(F) from 9% to >80%, tensile strength sigma(T) from 11 kPa to 315 kPa, and thermal conductivity lambda from 13.5 mW/m K to 24.5 mW/m K. The failure mode of the aerogels was observed to be density dependent and transition with increasing density from ductile compaction to elastic deformation to brittle fracture. Within the density range where elastic behavior was observed, the compressive strength of the silica aerogels was measured to be roughly one order of magnitude higher than would be expected from brittle materials due to the materials ability to absorb energy; these aerogels recovered elastically after being subjected to compressive strains as high as 40%. BET analysis using nitrogen adsorption revealed specific surface areas of approximate to 740-780 m(2)/g and average pore sizes in the range of 26-72 nm. (C) 2013 Elsevier Inc. All rights reserved.