V. Flores Luque

Rheological behaviour of aqueous systems containing polyoxyethylene fatty alcohols with different HLB

ABSTRACT In this paper the influence of several factors on the rheological behaviour of aqueous systems containing 0.25 and 0.50 mol(L of a polyoxyethylene fatty alcohol has been analysed. Such factors are: temperature, pH, kind of alkali used to increase the pH and HLB of the surfactant. The influence on the rheological parameters when samples are introduced into the sensor systems either as liquids or as liquid crystals has also been studied. The experimental results have shown that the studied systems present Newtonian, pseudoplastic or plastic-pseudoplastic rheological behaviour at steady state shear. A photomicrographic study for systems having a plastic-pseudoplastic behaviour was carried out in order to find out if lyotropic mesophases were present. The results are discussed in relation to the effects that the above mentioned factors exert on the shape and size of the aggregates

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

The 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.