Specific viscosity of Newtonian aqueous solutions containing an anionic surfactant and an alkaline pyrophosphate

Abstract

AbstractThe effects that both temperature and solute concentrations exert on specific viscosity are studied in this paper. The products used were sodium or triethanolammonium dodecylsulfates or dodecylbenzenesulfonates, as surfactants, and tetrasodium or tetrapotassium pyrophosphates, as electrolytes. All are of technical quality. As temperature decreases, within the temperature range studied, a phase separation or an appearance of non‐Newtonian behavior is noted in many solutions. The solutions studied fit, within the accuracy range for experimental measurements, an empirical equation that agrees with what is called the activated diffusive relaxation model. For this model, the relative viscosity is a linear superposition of stresses coming from hydrodynamic interactions and from activation energy due to structural relaxation of the uniform distribution of micelles in the quiescent micellar solution. Solutions containing a dodecylsulfate show very slight hydrodynamic effects. Their activation energy, which is independent of temperature, becomes greater by increasing the concentrations of surfactant and pyrophosphate. The specific viscosities of these solutions also increase by replacing the triethanolammonium counter‐ion with sodium. Solutions containing sodium dodecylbenzenesulfonate show considerable hydrodynamic effects, which increase with the addition of tetrasodium pyrophosphate. The activation energy is independent of temperature. Solutions containing triethanolammonium dodecylbenzenesulfonate show decreasing activation energy values when temperature is increased. Consequently, a maximum for specific viscosity appears at a certain temperature. This maximum diminishes progressively with the addition of pyrophosphate, while the corresponding temperature becomes higher. From the investigation carried out, the necessity for further basic studies remains clear. Research should be done on concentrated aqueous solutions containing surfactants and electrolytes, taking into consideration the variations that their dynamic viscosities present along with composition and temperature. All of this, naturally, must be carried out before developmental research on manufacturing, commercialization and usage of such solutions proceeds.