Comparison of oleyl and elaidyl isomer surfactant–counterion systems in drag reduction, rheological properties and nanostructure

Compared with quaternary ammonium cationic surfactants with saturated alkyl chains, quaternary ammonium cationic surfactants with one double-bond in their alkyl chains, when mixed with appropriate counterions (in certain molar concentration ratios, ξ), can reach much lower effective drag-reduction temperatures, while maintaining the upper drag-reduction temperature limit of the corresponding saturated drag reducing surfactant solutions. No previous study has compared the effects of cis- vs. trans-unsaturated alkyl hydrocarbon tail configurations (oleyl vs. elaidyl) trimethyl ammonium chloride cationic surfactants at different counterion/surfactant concentration ratios on micellar nanostructures, 1H NMR spectra and on rheological and drag-reduction behavior of their solutions. Since neither pure oleyl (cis-) nor elaidyl (trans-) trimethyl ammonium chloride surfactants are commercially available, they were synthesized and their 5 mM solutions with NaSal counterion at concentrations of 5 mM, 7.5 mM and 12.5 mM were studied.

Schematic view of cis- and trans-forms of surfactant hydrocarbon chains.Figure optionsDownload high-quality image (37 K)Download as PowerPoint slideResearch highlights
► Presented the first drag reduction, rheological and nanostructure comparisons of unsaturated (cis/trans) cationic surfactant/counterion systems.
► 1H NMR results indicate that the hydrocarbon chain of the cis surfactant is more favorable for micelle growth than the trans surfactant.
► The oleyl surfactant drag reducing system had greater resistance to mechanical shear than the elaidyl surfactant.
► Confirmed that viscoelasticity is not required for a surfactant system to be drag reducing.
► High extensional viscosity is a major factor in the drag reduction mechanism.