Influence of the filler content on the free nanohole volume in epoxy-based composites

A study on free nanohole volumes in particulate epoxy matrix composites as a function of the aluminum particles content is presented. Specifically, the influence of the filler content in the epoxy matrix on the nanohole volume is analyzed in terms of the mechanical and morphological properties of the composites fabricated. Nanoholes data were measured using positron annihilation lifetime spectroscopy recently published by the authors. Applying the Park-Earmme micromechanical model, these data are interpreted in terms of the thermal stresses generated during the curing process applied during fabrication. Some input parameters of the model were experimentally obtained. In order to obtain a satisfactory description of the evolution of the free nanohole volume in the whole range of filler contents, a contribution due to the matrix-particle interphases is taken into account in the micromechanical model. To this aim, specific information on the interphases was obtained using atomic force microscopy (AFM), scanning electron microscopy (SEM), differencital scanning calorimetry (DSC) and a free-constraint analysis of the positron lifetime data.