​Some surfactants with specific architecture can self-assemble into wormlike micelles (WLMs) that show viscoelastic response macroscopically due to the entanglement of the WLMs. These surfactants are also called viscoelastic surfactants (VES) and they have been used in applications from oil production and drag reduction to personal care. Most of the documented results on VES are obtained at room temperature or high temperature.

However, few studies have been reported on the WLMs formed under sub-zero temperatures, cryo-VES fluids, mainly due to the limitation of the instruments available for use in freezing environment. In this study, the researchers made a series of cryo-VES fluids and found from rheological testing that they showed viscoelastic behaviours sub-zero temperatures, and increased viscosity upon decreasing the temperature.

To gain insight into the microstructures of these cryo-VES, with the aim of explaining these macroscopic responses, deuterated versions of these fluids were characterised by the ISIS deuteration facility, and small angle neutron scattering (SANS) experiments were designed and performed on Loq between 20 and -20 °C. The cryo-SANS results revealed that WLMs could still be formed at extremely low temperature, and the viscosity change is due to the transformation from spherical to worm-like micelles that occurs when decreasing the temperature.

This study is the first to describe cryo-WLMs, and the first to characterise micellar microstructures using cryo-SANS. These cryo-VES fluids may find potential use in hydro-fracking operations in arctic areas and aircraft de-icing fluids, replacing traditional polymer-based counterparts.