Silica sol as a nanoglue: Flexible synthesis of composite aerogels

Low-density nanoscale mesoporous composites may be readily synthesized by a dding a colloidal or dispersed solid to an about-to-gel silica set. The sil ica sol can "glue" a range of chemically and physically diverse particles i nto the three-dimensional silica network formed upon gelation. If the compo site gel is supercritically dried so as to maintain the high porosity of th e wet gel,:a composite aerogel is formed In which the nanoscopic surface an d bulk properties of each component are retained in the solid composite. Th e,volume fraction of the second solid can be varied above or below a percol ation threshold to tune the transport properties of the composite aerogel a nd thereby design nanoscale materials for chemical, electronic, and optical applications.