Flexible RF und carbon aerogels

Abstract

Organic resorcinol - formaldehyde (RF) aerogels dried under ambient conditions with a large resorcinol (R) to catalyst (C) ratio are usually hard and brittle with strength about 100 kPa and Young’s-moduli in the range of 1-2 MPa and densities in the range of 0.2 to 0.4 g/cm3. We observe that special conditions of aerogel preparation yield surprisingly flexible aerogels. They can be bent easily, similar to the well-known flexible silica aerogels. They have a low density about 0.06 g/cm3, a very low elastic modulus of around 70 kPa and are elastically deformable by more than 40% in an almost reversible manner. The thermal conductivity of these aerogels is around 0.046 W/(mK). The flexible RF-aerogel shows a continuous network of particles with sizes of around 1 µm and pores of about 10 µm. Carbonization of the flexible RF aerogels leads to flexible carbon aerogel pieces. This paper discusses the effect of resorcinol-water (R/W) molar ratio on the mechanical properties, pore structure and bulk density of flexible RF aerogels.