Smart dispersion: Validation of OCT and impedance spectroscopy as solutions for in-situ dispersion analysis of CNP/EP-composites

In this study, we demonstrate the applicability of three-roll milling (TRM) process for carbon nanotube-epoxy dispersion in industrial scale and two methods to characterize the dispersion quality based on optical coherence tomography (OCT) and impedance spectroscopy were utilized. These methods are easily applicable for industrial continuous TRM dispersion process monitoring. Modeling impedance spectra with equivalent circuit enhances the possibility to quantify the grade of dispersion. We monitored the dispersion development over a complete seven step three-roll mill process for several batches. The gained results are in good accordance to the particle size measurements by grindometry. Results show, on the one hand, that the real part of impedance undergoes a minimum during processing. The most homogeneous dispersion state is not the favorable for gaining electrical conductive materials. On the other hand, imaginary part of impedance undergoes a maximum. High reactance correlates with small particle sizes as well as homogeneous distribution. A developed model from impedance spectra leads to an improved understanding of network formation. OCT results allow a qualitative analysis of the dispersion and detection of in-homogeneous agglomerate sizes.