Detection of charges at the interphase of polymeric nanocomposites

The use of nanoscale filler in polymeric insulating materials can lead to a modification of macroscopic material properties which is attributed to the properties of the interphase between the nanoscale filler particles and the surrounding polymer. In the present study, the interphase of two kinds of nanoscale silica particles embedded in silicone rubber was investigated with Electrostatic Force Microscopy (EFM). The phase signal measured above the particle and the adjacent polymer show a parabolic dependence on the tip voltage and a characteristic shift between each other. By numerical simulation with a 3D model it could be shown that the presence of a charge at the particle would result in such a parabolic dependence on the tip voltage, and that the vertical and horizontal shift depend on the charge magnitude. From electrostatic considerations it is known that charges could be present subject to a number of unknown parameters like contact potential differences, capacitive coupling and other measurement parameters. By eliminating the unknown parameters in the relevant formulae it could be shown that charges are present at particles, thus giving evidence that an electric double layer around the particles in polymeric nanocomposites exist.