A micromechanical study on the existence of the interphase layer in particle-reinforced nanocomposites

Abstract

In this paper, the effective elastic properties of nanoparticles reinforced nanocomposites including effects of an interphase layer around the nanoparticles are determined using analytical micromechanical approach. The present micromechanical model is based on the Green’s function and the interface operator. By using the interface operator, the interphase layer and the nanoparticle are combined as a single spherical inclusion and then the effective properties of the composite are calculated by using the Green’s function. To assess the presented method, epoxy-silica nanocomposites are thoroughly studied in this paper. Since there is no direct method to determine physical and mechanical properties of the interphase layer, we have presented a method to determine these properties, namely volume fraction and elastic modulus of the interphase layer, for epoxy-silica nanocomposites by correlating the experimental data for effective elastic properties of the epoxy-silica nanocomposites and those obtained by the presented model. Applying the presented method to various experimental data available in the literature, epoxy-silica nanocomposites are characterized into nanocomposites with, and without an interphase layer. The presence or absence of the interphase layer is concluded by the value of its volume fraction determined by the present method. It is observed that nanocomposites with surface-modified silica nanoparticles yield perfect bonding with the matrix and do not form an interphase layer. On the other hand, nanocomposites with raw silica nanoparticles (without surface modification) yield an interphase layer between the nanoparticles and the matrix which is softer than the matrix.