Surfactants have the ability to self-assemble in most of the aqueous solutions to form microstructures, such as, spherical micelles, cylindrical micelles, vesicles, and other structures.
Cylindrical micelles are also called worm-like micelles. These micelles form in many aqueous surfactant systems, with or without the presence of salt, when the surfactant packing parameter is favorable, Ns [= v/(l*a0)], is between 0.33-0.5, where v is the volume of the hydrophobic portion of the surfactant, l is the length of the hydrophobic chain, and a0 is the effective area of the head group. Worm-like micellar solutions are often viscous due to entanglement while spherical micellar solutions are not viscous.
We were interested to study surfactants which form worm-like micelles. Worm-like micellar solutions are viscous so can be used as a substitute of polymers for mobility control during oil production if they are oil tolerant. So, a new class of surfactants was synthesized and investigated under various temperatures (20-125 oC) and salinity conditions (up to 250,000 ppm TDS). Aqueous stability, rheology, CryoTEM imaging, and dynamic-light-scattering measurements were performed to understand properties, shape and size of the micelles formed using these surfactants under different temperature and salinity conditions. Crude oils and other hydrocarbons were mixed with the aqueous surfactant solutions and the oil tolerant was studied. The properties of these surfactants were compared with those of a few conventional surfactants that form worm-like micelles. The result showed that one of the surfactants (MeO-70PO-100EOH) can tolerate crude-oil or hydrocarbon up to 8 volume percent. Also, the result showed that heavier hydrocarbons had less effect on the viscosity on these worm-like micellar solutions in comparison to lighter hydrocarbons.
- Panthi, K.; Sharma, H., Weerasooriya, U. P.; Mohanty, K. K. 2020. Oil-Tolerant Nonionic Worm-like Micellar Solution. ACS Omega. 2020, 5, 30817-30825.
