Linear wormlike micelles exhibit behaviors similar to ordinary polymers in strong saline flows

Micelles are a unique class of molecular aggregates, consisting of molecules with a hydrophilic head and a hydrophobic tail. When dispersed in saline solutions, micelles elongate into wormlike structures and assemble into various arrangements, and sometimes eventually becoming entangled. These wormlike micelles are widely used in everything from household products and cosmetics to the oil and gas industry, where they are subjected to shear flows as they are pumped through long, complex pipes during processing.

To better understand the impacts of these processes, Gaudino et al. studied the effects of shear flows on linear micelles with varying salt concentrations. Surprisingly, they found that regardless of their chemical structure, the micelles behave similarly to ordinary polymers.

“The living nature of the wormlike micelles is somehow hidden in shear start-up experiments,” said author Rossana Pasquino. “Entangled linear wormlike micelles appear to align, stretch and tumble just like polymeric chains.”

With increasing salt content, the wormlike micelles become longer and more and more entangled. Similar to a polymeric system, the micelles exhibit shear-thinning behavior and stretch out after the shear rate exceeds a threshold value. As anisotropy increases, both micellar systems and ordinary polymers exhibit an overshoot in viscosity before approaching a steady state.

Looking ahead, the group plans to study other properties of wormlike micelles whose physical mechanism is not yet understood. Specifically, while the present work focuses on linear wormlike micelles, branched wormlike micelles are a more complicated architecture that requires further investigation.

Source: “Linear wormlike micelles behave similarly to entangled linear polymers in fast shear flows,” by Danila Gaudino, Salvatore Costanzo, Giovanni Ianniruberto, Nino Grizzuti, and Rossana Pasquino, Journal of Rheology (2020). The article can be accessed at https://doi.org/10.1122/8.0000003 .