Effect of filler structure on the dielectric and thermal properties of SiO2/PTFE composites

The effects of fillers’ structure on microstructure, dielectric and thermal properties of the SiO2/PTFE composite were investigated. The composites were prepared by a calendering and hot-pressing process, and their dielectric, thermal properties of composites with various SiO2 fillers were studied. The morphologic analysis shows that open pores on the particles’ surface improve the interfacial adhesion between silica and PTFE without any chemical coupling agent. With the increase of the silica fillers content, the dielectric constants and dielectric losses of the composites increase gradually, while the thermal expansion coefficients decrease. The air phase in the porous fillers leads to low dielectric constants of the composites effectively. Bruggeman’s equation analysis indicates that solid-air interfaces influence the dielectric properties of the composites via the interfacial polarization. The difference between CTE testing results and theoretic prediction reveals that the microstructures, such as interfacial adhesion and particle size distribution, play the key roles in the thermal properties. It is suggested that the combination design of the microstructure and the component is a multi-scale strategy to tailor the properties of composites optionally for developing functional composites.