Evaluation of interfaces of filled polymeric insulating materials with the Dielectric Spectroscopy

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In high voltage technology, insulation systems are increasingly made of synthetic materials, usually polymers filled with particles of microscopic size. Thereby, the inner interfaces influence the properties of the insulating material significantly. New developments indicate that polymers filled with particles of nanometric size have improved resistance to treeing, to high-voltage arcing as well as to tracking and erosion. It is assumed that these improvements are due to the special properties of the interphase, i.e. the area around the interface between particles and the polymer. So far, such interphase could only be demonstrated indirectly by the different properties of polymeric insulating materials with nanometric fillers compared to the unfilled material. Quite recently the existence of an interphase could be directly verified for the first time by measurements with the Atomic Force Microscopy. But, so far it is not certain, what are the properties of the interphase, what structure the interphase has and what is the role of free charge carriers, if any.The development of interphases depends on the filler, the matrix materials, and in particular the surface treatment of the filler particles. Interphases can be identified and characterized by their dielectric properties, i.e. the permittivity and the dielectric loss factor determined by the dielectric spectroscopy. In a dielectric spectroscopy the temperature of the material and the frequency of the applied field are varied over a wide range. Thus, the different polarization mechanisms can be distinguished from each other, revealing the structure of the investigated insulating material. The aim of the project is to use the dielectric spectroscopy to characterize polymeric insulating materials with micro- and nanosized fillers to enhance the understanding of the interaction between the particles and the polymer and to develop a model, which can then be used to explain the dielectric properties of polymeric insulating materials as well as their behavior under electrical stress. So, it would be possible to influence systematically the properties of filled insulating materials.