Viscoelastic Behavior of Alkyl Ether Sulfate Systems Containing Sodium Carbonate

Abstract

AbstractRelaxation behaviors in systems containing sodium alkyl ether sulfate and sodium carbonate were studied. The anionic surfactants were commercial grade systems with average chain lengths of twelve carbons and either one, two, or three ethoxy (EO) groups. It was found that viscosity maxima in the three systems were achieved at particular salt levels that increased with an increase in the number of EO groups. Relaxation of the optimized systems was studied by measuring the complex, storage and loss moduli as a function of frequency. Temperature was varied between 5 and 45 °C. While characterization of relaxation in terms of the Maxwell model adequately described data below the threshold of ωτ < 1, the model failed to adequately describe behavior at higher frequencies. A modified expression with an additional Rouse relaxation mode adequately described relaxation throughout the frequency range studied. Temperature dependencies provided estimates of activation energies which were consistent with literature values for reptation modes of relaxation. No temperature dependencies were seen for the second relaxation mode of the model. Studies of ultrasonic attenuation in the surfactant system determined that attenuation increased in systems with higher EO content. Relaxation times were additionally found to decrease with increased EO content. This implied that diffusion in the compressive relaxation modes was more dependent on the sizes of the micellar structures as opposed to the sizes of the individual surfactant molecules.