Modeling Micellar Growth and Branching in Mixtures of Zwitterionic with Ionic Surfactants

Abstract

Zwitterionic surfactants are widely applied as dragreducing or thickening agents because their aggregation patterns may drastically change in response to variations of the system composition or external stimuli, which provides controllable viscoelasticity. For predicting aggregation behavior of surfactant mixtures, classical molecular thermodynamic models have been widely used. Particularly, the results of modeling have been reported for zwitterionic/ionic surfactant mixtures. However, for solutions containing a zwitterionic surfactant, no molecular thermodynamic model has been proposed for a micellar branch. In this work we extend the classical molecular thermodynamic aggregation model to describe aggregation in the aqueous mixtures that contain a zwitterionic and an ionic surfactant. We derive analytical expressions (1) for the contribution of dipoles to the electrostatic term of the standard free energy of aggregation into micellar branches and (2) for the dipolar contribution to the persistence length of wormlike micelles. The dependence of micellar branching on the surfactant concentration is taken into account by including the population of micellar branches in the material balance equations. This model is applied to predict aggregation equilibrium in aqueous salt solutions of betaine (oleoylamidopropyl-N,N-dimethylbetaine) mixed with sodium dodecyl sulfate (SDS) and the longer tail sodium n-alkyl sulfates. We discuss the predicted properties of the aggregates and micellar networks and compare our predictions with available experimental data.

Prediction of Viscosity of the Oil–Surfactant–Brine Microemulsion Phase Using Molecular Dynamics Simulations

“…SDS molecules form small and spherical micelles at low concentrations, but as the concentration increases, the micelles grow and become elongated or rod-like and ultimately become entangled. This entanglement increases the viscosity of the microemulsion phase by hindering the movement of micelles. , The micelles become more compact and tightly packed for the concentration of SDS from 0.18 to 0.24 mol L –1 . This change in micelle structure, from a more dispersed state to a more compact state, influences the microemulsion’s flow behavior. , This phenomenon reduces the available space for the movement of micelles and leads to a decrease in the phase viscosity.…”

Influence of Surfactant Structure on Polydisperse Formulations of Alkyl Ether Sulfates and Alkyl Amidopropyl Betaines

“…Work by Victorov et al highlighted the role of curvature transformation in mixtures of alkyl sulfates and oleoylamidopropyl-N,N-dimethylbetaine, mixtures that produce similarly tunable wormlike micellar solutions. 38 They presented modeling that extended existing thermodynamic frameworks to consider (typically ignored) micellar branching and dipolar contributions to wormlike chain persistence. In the present work, this theory helps to contextualize the thermodynamic limitation as to why smaller-tailed alkyl ether sulfates pair with betaines to produce higher curvature systems that cannot extend to form worms.…”

“…Here, we propose that the inclusion of the linker has a minimal contribution the scission energy of SC 10 ES, and the energetic threshold required for a transition to a rod-like architecture. Work by Victorov et al highlighted the role of curvature transformation in mixtures of alkyl sulfates and oleoylamidopropyl- N , N -dimethylbetaine, mixtures that produce similarly tunable wormlike micellar solutions . They presented modeling that extended existing thermodynamic frameworks to consider (typically ignored) micellar branching and dipolar contributions to wormlike chain persistence.…”

Unusual Increasing Viscoelasticity of Wormlike Micelles Composed of Imidazolium Gemini Surfactants with Temperature

“…Wormlike micelles are long, cylindrical aggregates of surfactants, which have aroused great interest among scientists over the past 20 years due to their widespread use in industry and daily life. − These wormlike micelles usually entangle each other to form a transient network that imparts viscoelasticity to the solution. , The physical interactions among the wormlike micelles constantly break and reform, changing with the temperature and solution composition. − The change of the viscoelasticity of wormlike micelles with temperature has many advantages, such as the ease of temperature control and adjustment without the need for additives and easy preparation according to the change of the solubility of the surfactant at different temperatures or different interfacial activities. Normally, with increasing temperature, the mean micellar length of wormlike micelles exponentially decreases .…”