Mechanical and acoustical properties as a function of PEG concentration in macroporous silica gels

The pore size of macroporous silica aerogel can be controlled by varying the concentration of water-soluble organic polymers in the sol. These gels demonstrate a wide array of mechanical and acoustical properties in proportion to the organic polymer concentration in the sol. Presented in this paper are the resulting mechanical dependencies upon the concentration of high molecular weight polyethylene glycol (PEG) in the initial sol. Physical properties studied include density, surface area, pore structure, acoustic velocity, and mechanical strength. Most of these properties exhibited a large change when a small concentration of PEG was added to the initial sol, correlating with a strengthening of the solid matrix. Still higher concentrations of PEG progressively weakened the solid matrix. Through examination of the gels containing PEG, experiments have shown an inverse relation of acoustic velocity to PEG concentration while density remains relatively constant.