Synergistic Influence of pH and Temperature on Rheological Behavior of Adhesive Emulsions Stabilized with Micelle Dispersion of an Anionic Surfactant

Abstract

The influence of emulsion pH and temperature on the rheological behavior of adhesive oil-in-water (o/w) emulsions stabilized with an anionic surfactant (sodium dodecyl benzene sulfonate, SDBS) was studied. The flow properties of emulsions as a complex fluid were investigated using steady and dynamic rheometry for characterization of non-Newtonian behavior. Emulsion pH was varied from 2 to 12 and temperature was varied from 20 to 50 °C, respectively. The influences of the above-mentioned variables on the rheology of o/w emulsion were studied using steady-shear and dynamic oscillatory experiments. Various viscosity models (2, 3, and 4 parameter rheological model) were used to predict the rheological parameters. An increase in the pH of the emulsion led to an increase in the emulsion stability, viscosity, and viscoelastic properties (G′, G″, η*, and tan δ), and a decrease in the mean droplet size of the emulsion. A decrease in the temperature yields higher values of steady-shear viscosity and viscoelastic properties upon a decrease in droplet size. Emulsions were characterized as flocculated structured liquid exhibiting a characteristic crossover frequency (ω*) within the range of angular frequency studied in oscillatory measurements. Overall, emulsions exhibited non-Newtonian shear-thinning behavior and the synergy of pH and temperature significantly influences the emulsion rheology.