The rheological behavior of graphite oxide/cationic polyacrylamide suspensions
Cationic polyacrylamide (CPAM) is added into graphite oxide (GO) suspensions to purify the GO. A proper understanding of the best addition amount of CPAM and the rheological properties of GO/CPAM is important for filtration and the design of pumping systems for transportation. Both experimental and theoretical analyses are carried out with analysis of the high shear viscosity, shear thinning behavior and temperature dependence of GO/CPAM suspensions containing 1–40 wt% CPAM. With increase of the CPAM concentration, GO particles and the CPAM aggregate together to form floccules. The filtration and purification efficiency are improved when the GO/CPAM suspension contains 20 wt% CPAM and this is beneficial for pipeline transportation. The addition of CPAM can improve the thermal stability of GO to a certain extent, because the comparatively strong interface interactions block the decomposition of GO. The GO/CPAM suspension exhibits non-Newtonian characteristics. The Herschel–Bulkley model represents the GO/CPAM flow behavior accurately and the non-Newtonian flow characteristics of GO/CPAM are strengthened with a higher CPAM content. Correlations between the CPAM content, temperature, and viscosity are expressed using an exponential equation and a modified Arrhenius type equation, respectively. The activation energy for the flow process increases with the CPAM concentration. Furthermore, the dynamic tests indicate that the viscoelasticity of GO/CPAM decreases remarkably with decrease of the CPAM concentration. Under shearing, the GO/CPAM suspension exhibits thixotropic properties, while the network structure of GO/CPAM breaks down gradually. Then the viscosity decreases with time, causing flow acceleration due to an avalanche effect.