## 1 Introduction
It could thus be realized that techniques for the real-time characterization and study of the dispersion state and the quality of the CNT network during processing are essential for optimizing the dispersion process, as well as for the process of quality monitoring control. Since the nano- and micro-particle dispersion strongly affect the electrical properties of the composite, the results of electrical measurements can be directly connected with dispersion quality. Among numerous DC and AC electrical techniques, Impedance Spectroscopy (IS) utilizes an alternate excitation voltage over a wide range of frequencies, either by frequency sweep or Fast Fourier Transform (FFT). As a response of the material under test to the external field, a current is received to the IS analyzer. The resulting current is compared to the excitation voltage in terms of amplitude and phase delay, offering a complete view of the electrical properties as a function of the frequency of the medium. IS is characterized as a non-destructive technique, and is widely used for curing monitoring of thermosetting epoxy resins, damage analysis and Structural Health Monitoring (SHM) in composite materials [8; 32; 33; 34]. Another significant application of IS is the conductive nanoparticle dispersion monitoring in the polymeric resin matrix [14; 35]. [PERSON] et al. studied the effects of dispersion duration and filler type on the final electrical and mechanical properties of epoxy-based composites. The authors in this study used a two-part epoxy resin system, namely the LY5052 resin and the Aradur 5052 hardener, with Multi Walled Carbon Nano Tubes (MWCNTs) and milled CB. This composite system exhibited improved electrical and mechanical properties due to the exploitation of the synergistic effects of the different scale fillers in comparison to the composites reinforced by a single filler [14]. Furthermore, according to some studies, the enhanced properties of the nanocomposites with the same loading of nano- and micro-materials differs if the host type of the matrix is dissimilar [36; 37]. Considering these studies, an alteration of the matrix type may affect the properties of the final composites. This manuscript is focused on the development of a parametric study of polymeric nanocomposites and hybrid nanocomposites, containing MWCNTs and CB in Diglycidyl Ether of bisphenol-A (DGEBA) epoxy resin, to investigate the effects of the carbon particle dispersion in epoxy resin on the electrical and the mechanical properties. Dispersions were performed using a high-speed shear mixer. IS was utilized to monitor the final dielectric properties of composites produced under various dispersion protocols. These protocols were selected for a comprehensive study of the effects of the filler content and type, including the emergence of possible synergistic effects due to the combination of MWCNTs and CB, as well as the duration of the dispersion process to the final electrical and mechanical properties of the composites. Hence, fracture toughness of the composites was assessed through three-point bending on single edge notched beam specimens (SENB). Finally, Scanning Electron Microscopy (SEM) was utilized to study the failure mechanisms on the fracture surfaces of the SENB specimens regarding the influence of the reinforcement.