Temporally persistent networks of long-lived mixed wormlike micelles of zwitterionic and anionic surfactants

Rheometry, small-angle neutron scattering, and cryo-transmission electron microscopy were combined to investigate the structure and properties of mixed wormlike micelles (WLMs) of zwitterionic (oleylamidopropyl dimethyl betaine) and anionic (sodium dodecylsulfate) surfactants. This system demonstrates the formation of giant linear long-lived WLMs, which even at extremely low surfactant concentration reach a sufficient length to entangle with each other and form a three-dimensional temporally persistent network. Stability of these micelles can be due to electrostatic attraction between the headgroups of the anionic and zwitterionic surfactants and favorable volume/length hydrophobic ratio in the surfactant mixture. Heating of these systems leads to the transition of temporally persistent network with predominantly elastic properties into transient network exhibiting viscoelasticity, which is due to the shortening of long-lived WLMs. At increasing surfactant concentration, the long-lived linear micelles transform into fast-breaking branched micelles, which is due to the screening of electrostatic interactions by salt released from the dissociated surfactant molecules. The transition results in the drop of viscosity and approaches the system to the behavior of Maxwell fluid with a single relaxation time. The observed structural transitions strongly affecting the rheological properties can be exploited in various applications of zwitterionic surfactants. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

Rheometry, small-angle neutron scattering, and cryo-transmission electron microscopy were used to investigate the structure and properties of mixed wormlike micelles (WLMs) of zwitterionic and anionic surfactants. The study found that the transition of linear micelles into branched micelles at increasing surfactant concentration leads to a drop in viscosity and approaches the system to the behavior of Maxwell fluid with a single relaxation time, which strongly affects the rheological properties and can be exploited in various applications of zwitterionic surfactants.