Rheology of poly(acrylic acid): a model study

In this study, we examine the rheological characteristics of poly(acrylic acid) (PAA) polymers in aqueous solutions at 20 °C using various techniques. We also develop a model to simulate the rheological behavior of the polymer solutions, because, in some applications, the polymer is required to be dispersed within a short period of time, during which high-shear mixing is commonly used to achieve the necessary level of homogeneity. The model, which involves consideration of reptation, relaxation of the chains by slippage or loop relaxation, and normal Rouse dynamics, is appropriately adapted to reflect the structural changes of the polymer molecules and then used to identify possible relationships between molecular structure and viscoplastic behavior. The simple theory for flexible polymers is modified to include the possibility of complex formation by association between neighboring polymer molecules. We conclude that, although the model is sensitive to the average molar mass of the polymer, additional and more extensive high-shear-rate data are required to explore fully the validity of the Rouse description. However, the scaling of the viscosity by the addition of an increased friction factor provides a reasonable description of the short-range motions observed.