The morphology of silica particles generated in situ in PDMS networks in the presence of two types of catalysts is evaluated by using different techniques including solid-state Si-29 MAS NMR, near-infrared spectroscopies and small-angle X-ray scattering. The interactions with the poly(dimethylsiloxane) chains are examined through the swelling properties and thermal characteristics (in particular crystallization process) of the composites. In addition, H-1 NMR is used to investigate the adsorption layer of reduced mobility on the particle surface. © 2005 Elsevier Ltd. All rights reserved.