Small-angle neutron scattering (SANS) and transmission electron microscopy (TEM) were used to investigate the structure of pyrogenic silica in epoxy-based sub-microcomposites. Pyrogenic silica exhibits a fractal-like structure that can be characterized accurately by SANS. Two series of networks were synthesized. In the first series the specific surface area of pyrogenic silica varied from 50 to 300 m(2)/g. In the second series, the silica surface was modified in order to be able to react covalently with the precursors of the epoxy network. (c) 2006 Elsevier Ltd. All rights reserved.