The yielding behavior of aqueous solutions of Carbopol and triethanolamine and its prediction considering the fractal nature of the formed aggregates

Abstract

Materials with viscoplastic characteristics have been widely studied due to their applicability in various industries, but also because they are common in nature. The flow curve of viscoplastic fluids is generally well-captured by the Herschel-Bulkley (HB) model, which can account for yield stress and has a power-law behavior after flow occurs. Carbopol solutions are the most common kind of fluids used in experimental studies involving viscoplastic behavior. Carbopol solutions generally need a neutralizing agent, which acts as a pH regulator and prevents the formation of fungus. However, this agent can also affect the rheological properties of the original solution. In this work, yield stress measurements from different techniques (flow curve, oscillatory, and creep tests) were conducted for a combination of Carbopol and triethanolamine (neutralizing agent) concentrations of aqueous solutions. In addition, pH measurements for all samples were performed. For the analyzed cases, it was found that triethanolamine concentrations must be higher than 500 ppm to avoid the formation of fungi but below 700 ppm to obtain a homogeneous solution. The yield stress was shown to increase with the increment in the concentration of both components. In a more fundamental analysis, we employed the Suspension of Fractal Aggregates (SoFA) model, conceived to represent waxy crude oils, to evaluate the system considered and found an accurate agreement with respect to the data. This result shows that there can be similarities between the dynamics of both aggregate structures, to be verified in future studies.