Predicting the effect of additives on wormlike micelle and liquid crystal formation and rheology with phase inversion...

Surfactant-based viscoelastic fluids are used in consumer products such as body wash, cosmetics, and in hydraulic fracturing fluids to suspend proppant, among others. The solubilization of oil within these fluids changes the curvature of the surfactant and their nanostructure and rheological properties. The curvature-based hydrophilic-lipophilic-difference + net-average-curvature (HLD-NAC) framework may be able to quantify curvature changes and predict the formulation conditions required to obtain viscoelasticity.

Phase inversion experiments were conducted for combinations of commercial-grade C₈, C₁₀ and C₁₂ tetrapropylene glycol ether sulfate (extended) surfactant and sodium dihexyl sulfosuccinate with oil to obtain the HLD-NAC parameters. Wormlike micelles (WLMs) and liquid crystals (LCs) were then formulated and characterized. The transition from spherical micelles to WLMs/LCs at different oil contents was identified and compared with phase transitions predicted via the HLD-NAC model.

The spherical micelle to branched WLM/LC transition in surfactant + oil systems coincided with the water-continuous (Type I) to bicontinuous (Type III) microemulsion phase transition predicted with the HLD-NAC model. Using this finding, the transition of commercial-grade sodium laureth sulfate (SLES) micelles to viscoelastic LCs containing various oils was predicted using the HLD-NAC. The HLD-NAC also predicted the presence of a secondary peak in viscosity obtained in "salt curves" experiments associated with branched WLMs and LCs.