Polymer composites with a large nanofiller content: a case study involving epoxy

A situation involving a polymer nanocomposite containing a large amount of inorganic filler was studied. An epoxy nanocomposite with a content of 20% wt of nanosilica was used. Emphasis was put on imaging at the nanoscale and some dielectric responses were measured using dielectric spectroscopy. Using Transmission Electron Microscopy (TEM) in a High-Angle Annular Dark Field (HAADF) scanning mode, an area of less than 4 nm around an isolated particle was imaged and found to have a very low atomic number. With Atomic Force Microscopy (AFM) in peak-force mode agglomerates were clearly imaged. With respect to the dielectric response, no interfacial relaxation peak was observed. In presence of some agglomeration, the real part of the permittivity was found to be decreased by the addition of the nanofiller. Higher-field measurements unravelled nonlinear variations of the conduction versus an applied field. It was shown that the use of a large filler concentration resulted in greater interphase overlapping between the nanoparticles.