SAXS investigations on organic aerogels

Structural properties of organic aerogels were studied by ultra-small-angle X-ray scattering (USAXS) at the Synchrotron Radiation Laboratory HASYLAB at DESY, Hamburg, Germany. The organic aerogels were synthesized from the base-catalyzed sol-gel polymerization of resorcinol with formaldehyde (RF) followed by a supercritical drying process. RF aerogels are low-density materials with a solid matrix composed of interconnected colloidal-like particles. Scattering experiments were carried out using a crystal camera optimized for ultra-small-angle X-ray scattering with synchrotron radiation. The measured SAXS profiles revealed a scattering power depending upon synthetic conditions of the gels. RF aerogels were found to be homogeneous at length scales greater than 20 nm. From Guinier plots, radii of gyration R_g of 3-20 nm were computed. R_g appears to be a measure of the pore (cell) size. Although fractal silica aerogels show similar characteristics, fractal behavior of the organic aerogels is uncertain. These materials are best described as random aggregates of smooth colloidal like particles with open-cell porosity.