Rheology of polymeric suspensions: Polymer nanocomposites and waterborne coatings

The complexity inherited in the polymeric suspensions makes prediction and control of their rheological properties difficult. Much effort has been devoted to characterize these properties and considerable improvements have been made. However, much more work is desired in order to develop new products and understand the underlying knowledge about the flow behavior of the suspensions. In this work, the rheology of two types of polymeric suspensions, namely waterborne coatings and polymer/nanoclay and polymer carbon nanofibers has been studied.;As the waterborne coatings are non-Newtonian, the viscosity depends on the shear rate and the strain history, which makes the flow in circular pipes complicated. The rheology of a type of metallic automotive basecoat is measured using a highly accurate rheometer and the data is fitted to several constitutive models. The pressure drop of the paint flow in a straight circular pipe has been measured in a pilot plant, and the steady state laminar flow pressure drop over the pipe length has been calculated using numerical methods. Sisko model and Carreau model has been found to be able to predict the pressure drop accurately using the material parameters obtained from rheological measurements. The power law model is applicable for flows where the Reynolds number is less than 100. The effects of thixotropy can be neglected during normal continuous operation. The relatively higher initial pressure drop caused by the thixotropy of the paint occurs during start up is found to be 1.25 times the pressure drop at steady state. The paint studied shows abnormal temperature effects on the rheology. Steady shear viscosity decreases from 10 to 35 °C, and then increases at higher temperatures up to 45 °C.;In the study of the rheology of carbon nanofiber (CNF) suspensions in Newtonian fluids, it is found that the dispersion of the nanofibers determines the suspension rheology. The suspensions contain up to 5wt% CNFs. Steady shear viscosities of untreated sonicated suspensions are higher than that of better dispersed treated sonicated suspensions, due to the existence of large clumps and strong inter-particle interactions that block the flow. The measurements of small amplitude oscillatory shear and yield stress reveal that the both untreated sonicated and treated sonicated suspensions exhibit solid-like behavior when the nanofiber concentration is higher than 2wt%. Morphology investigations show that the acid treatment of the treated nanofibers disintegrates the agglomerates exists in the as-received CNFs and therefore improves dispersion, it also weaken them, as the subsequent sonication break most of the treated CNFs. (Abstract shortened by UMI.)...