Ultralow Percolation Threshold in Aerogel and Cryogel Templated Composites

We demonstrate a novel concept for preparing percolating composites with ultralow filler content by utilizing nanofiller-loaded aerogel and cryogels as a conductive template. This concept is investigated for several porous systems, including resorcinol-formaldehyde (RF), silica, and polyacrylamide (PAM) gels, and both graphene and carbon nanotubes are utilized as nanofiller. In each case, a stable, aqueous nanofiller dispersion is mixed with a sol-gel precursor and polymerized to form a hydrogel, which can then be converted to an aerogel by critical point drying or cryogel by freeze-drying. Epoxy resin is infused into the pores of the gels by capillary action without disrupting the monolithic structure. We show that conductive graphene/epoxy composites are formed with a very low graphene loading; a percolation threshold as low as 0.012 vol % is obtained for graphene-RF cryogel/epoxy composite. This is the lowest reported threshold of any graphene-based nanocomposites. Similar values are achieved in other aerogel and nanofiller systems, which demonstrates the versatility of this method.