Carbon black is widely used as a filler in order to modify the mechanical or the electrical properties of polymers. Such composites display significant non-linear effects. Moreover, examination of the large number of papers devoted to the physical properties of carbon black filled polymers indicates that each composite, even composites apparently consisting of similar matrixes and similar carbon blacks, may behave differently when prepared by different mixing methods. The present work aims to show that these particular behaviors can be related to the fact that carbon blacks used for composites arc mass fractals of low dimensionality (D_f <2) that arc able to interpenetrate each other to an extent that depends on the filler-matrix surface interaction and on the volume fraction of filler. Small-angle X-ray scattering (SAXS) is a convenient method for studying disordered systems at length scales ranging between a few tenths and a few hundred nm. SAXS is therefore particularly advantageous for exploring the morphology of carbon black aggregates and their degree of interpenetration when dispersed in a matrix. Furthermore, the use of an area detector yields two-dimensional images and hence information about anisotropy of the arrangement of scatterers. It is shown that this arrangement profoundly influences the physical properties of the composites. Analysis of SAXS curves obtained for a rubber grade carbon black (N330) and for composites prepared by dispersing it into polyethylene or EPR will be presented. As an example, the temperature and frequency dependence of the electrical conductivity will be discussed and compared to theoretical models. Finally, the mutual consistency of the electrical and mechanical behavior, theoretical models and information deduced from the scattering curves will be shown.
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