Characterizing the interphase dielectric constant of polymer composite materials: Effect of chemical coupling agents

Recent research into the dielectric characteristics of polymer-ceramic composites has shown that the interphase region of the composite can have a dielectric constant significantly different from that of the polymer phase due to covalent bonding of the polymer molecules to the surface of the filler particles. Chemical coupling agents and surfactants such as functional silanes, organotitanates, organometallic chelating agents, phosphate esters, and various ionic and nonionic organic esters are commonly employed to enhance the compatibility between the polymer phase and dispersed filler phase of composite systems. Using experimental data and molecular dipole polarization calculations, we determine the effect of such coupling agents on the interphase dielectric constant. Our results show that the addition of functional silane coupling agents or nonionic surfactants at concentrations of 0.5 wt % or less of the total organics of a polymer-ceramic composite system has significant effects on the dielectric constant of the interphase region, yet has little or no effect on the dielectric constant values of the polymer phase. Furthermore, the chemical bonding of the coupling agents to the ceramic filler particles determine the dielectric constant of the interphase region as predicted by chemical polarization calculations. These results are fully consistent with experimental evidence and further validate the use of molecular polarization calculations of composite interphase regions to determine and predict the overall effective dielectric properties of packaging materials for a wide range of electrical, electronic, and rf applications. (C) 2003 American Institute of Physics.