Oil-Tolerant Nonionic Worm-like Micellar Solution.

The goal of this work is to study the effect of crude oil on worm-like micelles and identify any oil-tolerant systems. A new class of nonionic surfactants was synthesized that forms viscous worm-like micelles under a wide range of temperature and salinity conditions. Aqueous stability, rheology, cryogenic transmission electron microscopy imaging, and dynamic-light-scattering measurements were performed to understand properties, shape, and size of the micelles formed using these surfactants under different temperatures and salinity conditions and in the presence of hydrocarbons. These micellar solutions maintained high viscosity in the presence of small amounts (up to 8 vol %) of crude oils and pure hydrocarbons. Similar experiments were performed with conventional surfactant systems that were known to form worm-like micelles; they did not show oil tolerance. Larger alkanes and viscous crude oils affect the viscosity and transformation of cylindrical micelles less. These new surfactants are useful for oil and gas operations such as hydraulic fracturing, conformance control, and mobility control as they form viscous worm-like micelles in the presence of small amounts of crude oils.

Multistimuli-Responsive Foams Using an Anionic Surfactant.

In this work, we report a novel class of a commercially available surfactant which shows a multistimuli-responsive behavior toward foam stability. It comprises three components-a hydrophobe (tristyrylphenol), a temperature-sensitive block (polypropylene oxide, PO), and a pH-sensitive moiety (carboxyl group). The hydrophobicity-hydrophilicity balance of the surfactant can be tuned by changing either the pH or temperature of the system. At or below pH 4, the carboxyl functional group is dominantly protonated, resulting in zero foamability. At higher pH, the surfactant exhibits good foamability and foam stability marked with a fine bubble texture (∼200 µm). Foam destabilization could be achieved rapidly by either lowering the pH or bubbling CO2 gas. At a fixed pH in the presence of salt, increasing the temperature to 65 °C resulted in rapid defoaming because of the increased hydrophobicity of the PO chain. This stimuli-induced stabilization and destabilization of foam were found to be reversible. We envisage the use of such a multi-responsive foaming system in diverse applications such as foam-enhanced oil recovery and environmental remediation where spatial and temporal control over foam stability is desirable. The low-cost commercial availability of the surfactant further makes it lucrative.