Viscosity as a Measure of Dispersion State of Carbon Nano Fibers in Epoxy Matrix

To maximize the effect of addition of carbon nano fibers (CNFs) into the polymer, well dispersion of CNFs during the fabrication process is inevitable. Various techniques like ultra-sonication, calendaring and high pressure homogenizing can be used to overcome the challenge of dispersion. Despite the ease of applying ultra-sonication, it causes shortening the length of CNF which leads to decrease in the aspect ratio of particles and thus reduction in the enhancement of properties. Ability to determine the suitable sonication conditions is the key to fabricate a nanocomposite with welldispersed CNFs. In this research, the viscosity of polymer solution (epoxy and CNF) is a parameter which is used to determine the suitable sonication duration. Change of viscosity within the sonication time at other constant sonication conditions (output power, cycle, probe size, etc.) is used to indicate when almost well dispersion of nanoparticles is achieved (optimum sonication time). In this article, the effect of addition of various CNF contents namely, 0.15, 0.25 and 0.4 wt.% on the viscosity of epoxy is studied. The results indicate that by introducing more filler, the increase in the viscosity can be seen and the suitable sonication time increases. In addition, scanning electron microscopy of the fracture surface of nanocomposites is applied to investigate the dispersion state of CNFs in the matrix. Furthermore, epoxy filled with 0.25 and 0.4 wt.% has been prepared in different sonication times to evaluate the effect of sonication time on the mechanical properties of nanocomposites. The results of tensile experiments show that the maximum tensile strength and viscosity can be achieved in the optimum sonication time. Therefore, the present method can be used to determine the optimum sonication time and hence increase the mechanical properties of reinforced polymers with nano fillers.