The analysis of the fluorescent response from the dansyl moiety as a function of temperature has been used to estimate the thermal transitions in silica particle/epoxy-based composite materials. Silica particles were surface-coated with 3-aminopropyltriethoxysilane (APTES) and 3-aminopropylmethyldiethoxysilane (APDES). 5-Dimethylamino-1-naphtalenesulfonyl chloride (DNS) and 5-dimethylaminonaphthalene-1-(2-aminoehyl)) sulfonamide (DNS-EDA) were selectively attached to the silanized silica particles and to the epoxy matrix respectively. The fluorescence results, interpreted in terms of the model of interpenetrating polymer networks, suggest that (i) independent of the silane coating, the interfacial region is slightly more rigid and heterogeneous than the epoxy bulk and (ii) the interface generated with APTES seems to be more flexible than that obtained with APDES. (C) 2004 Elsevier Inc. All rights reserved.