Rheology of Aqueous Solutions Containing SLES, CAPB, and Microemulsion: Influence of Cosurfactant and Salt

Abstract

Aqueous solutions containing sodium lauryl ether sulphate (SLES) and cocamidopropyl Betaine (CAPB) with a constant total surfactant concentration (10 wt%) but different volume mixing ratios were prepared. A remarkable increase in the solutions' viscosity at a volume mixing ratio of 34 v/v% SLES to 66 v/v% CAPB was observed. By increasing the volume ratio of SLES (r-value) in the binary mixture, the viscosity of 10 wt% SLES, which is close to that of water, increases to a maximum, but then drops down drastically at high r values (>45 v/v%). The maximum viscosity (V max ) is 2.8 Pas, whereas the minimum is 2 mPas. The rheological behavior at V max has the remarkable feature of a simple Maxwell fluid over a large frequency range with one relaxation time. By adding a microemulsion (Plantasil Micro), the value of V max decreases extremely, whereas adding cosurfactants like isodecyltrietheleneoxide (IT 3 ) or salts, like calcium chloride, leads to a pronounced increase in the value of V max . At 0.76 wt% CaCl 2 , V max is 140 Pas and 150 Pas in the presence of 1 wt% IT 3 . By increasing the SLES volume mixing ratio in the solution the maximum viscosity is shifted to higher CaCl 2 amounts. The increasing viscosity can be explained by a transformation of the micelle shape from spherical to rod-like. Whereas adding cosurfactants or salts leads to an increased entanglement between the rod-like micelles. Consequently, higher microemulsion amounts can be added before reaching the minimum viscosity.

In Situ Nanostructural Analysis of Concentrated Wormlike Micellar Fluids Comprising Sodium Laureth Sulfate and Cocamidopropyl Betaine Using Small-Angle Neutron Scattering

“…Previous scattering studies of SLES/CAPB systems indicate persistence lengths of 600 Å, for dilute (0.2 wt %) WLMs in 3–5 wt % electrolyte and with relatively large uncertainties in modeled contour lengths (±900 – 10,000 Å) . Rheological studies identified a sharp peak in the zero-shear viscosity for 10 wt % SLES/CAPB with a mass ratio of 34:66 without the electrolyte, indicative of a wormlike transition . The addition of electrolyte promotes the formation of WLMs at lower surfactant concentrations, and above a critical electrolyte concentration, semidilute solutions form a branched network that exhibits a significantly reduced viscosity .…”

“…Rheological studies identified a sharp peak in the zero-shear viscosity for 10 wt % SLES/CAPB with a mass ratio of 34:66 without the electrolyte, indicative of a wormlike transition . The addition of electrolyte promotes the formation of WLMs at lower surfactant concentrations, and above a critical electrolyte concentration, semidilute solutions form a branched network that exhibits a significantly reduced viscosity . Above the dilute surfactant regime, the low- q scattering gradient flattens with increasing surfactant concentration due to the additional inter-worm volume exclusion …”

The Relationship between Wormlike Micelle Scission Free Energy and Micellar Composition: The Case of Sodium Lauryl Ether Sulfate and Cocamidopropyl Betaine

“…WLM form at lower salt concentrations. 50 To ensure the validity of our CAPB model, a simulated salt curve for SLES 1 EO:CAPB at 11wt%, ratio 9.85 to 1.15 wt%, was generated, as in the work of Tang et al 34 All simulations for the salt curve were performed in NVT ensemble using DL MESO mesoscale simulation package 51 and all the systems were simulated in a cubic box with volume of 64 × 10 3 DPD unit length. Slater-type charge smearing was applied to the systems, as in previous works.…”

Impact of polyelectrolyte‐surfactant interactions on the rheology and wet lubrication performance of conditioning shampoo

“…Although the SLES–CapB surfactant system is extensively used for its rheological properties, there are not a lot of studies that characterize its rheology and microstructure [18–21]. Mitrinova et al .…”