Evidence of the interphase in epoxy nanocomposites

The improvement of electrical properties by adding nanoscale fillers to polymeric insulating materials is attributed to an interfacial area, the interphase, which is formed between the filler particles and the polymer matrix. Despite there are several models describing the interphase, a direct evidence for its existence in epoxy nanocomposites has not been provided so far. It is the aim of the present study to make the interphase visible. For this purpose nanoscale silica particles themselves and the same type of silica particles embedded in an epoxy nanocomposite were investigated by Atomic Force Microscopy (AFM) and Electric Force Microscopy (EFM). In the EFM images the filler particles appear larger when they are embedded in the composite material than they do when they are not embedded. This difference in size is attributed to the interphase surrounding the filler particles. By comparing the size of the filler particles themselves and the filler particles embedded in the composite material the thickness of the interphase is estimated. From the investigations it turns out that an interphase may be formed around filler particles in epoxy nanocomposites, and that AFM and EFM measurements are an appropriate method to make the interphase visible.