On the matrix-particle interphase in epoxy-based composites

A study on the interphase morphology in epoxy-based composites is presented. Composite samples containing a volume fraction of aluminum particles (typical sizes of 100 μm ca.) between 0% and 30% were prepared. As main experimental technique, differential scanning calorimetry (DSC) was used. Specifically, from the thermograms obtained for each composite, the differences between the heat flow at temperatures above and below the glass transition temperature were determined. From these data, for each composite, and following ideas suggested in the literature, the different thicknesses and volumetric fractions of interphase were estimated. The results obtained show that both morphological parameters strongly increase for a filler volume fraction above 15%. On the other hand, using positron annihilation lifetime spectroscopy technique, additional evidence allowed us to confirm the presence of an interphase region in the composites and estimate the associated free volume which was smaller than that corresponding to the epoxy matrix.