Carbomer Dispersions: A New Calibration Method for Quantifying Shear-Thinning and Shear-Thickening Effects

This article introduces a new method to quantify non-Newtonian behavior of polymer dispersions, while, at the same time, taking into consideration the instrumental accuracy for measuring rheological properties of such dispersions. As a case study, rheological properties of carbomer dispersions have been investigated as a function of carbomer concentration. Carbomer, 2-propenoic acid homo-polymer, is classified as a synthetic polymer and used as an emulsion stabilizer as well as an aqueous thickening agent. The apparent viscosity, eta, was measured as a function of shear rate for different carbomer contents. The calibration method introduces a dimensionless viscosity change, Theta((gamma) over dot), and a dimensionless change in shear rate, Phi. A straight-line relationship was used as a model to describe how Theta((gamma) over dot) changes as a function of Phi. The model, based on the proposed calibration method, managed to quantitatively and qualitatively describe the shear-thinning behavior of carbomer dispersions. Carbomer dispersions have vertical bar Theta((gamma) over dot)vertical bar values less than one for diluted concentrations (less than 0.45 wt% carbomer). Above this threshold, carbomer dispersions exhibited a non-Newtonian behavior manifested by vertical bar Theta((gamma) over dot)vertical bar values greater than one.