Bridging microstructure to macroscale turbulent drag reduction: Mechanisms and shear resistance of oil-soluble surfactant

Polymers with high molecular weights can significantly reduce the frictional drag in turbulent flow. However, under the strong hydrodynamic force of turbulent flow, chains of the polymer's macromolecules may undergo significant mechanical degradation, leading to a loss of drag reduction effectiveness. This paper proposes using oil-soluble surfactants for turbulent drag reduction in oil transport. By disk rheometer experiments and molecular dynamics simulations, four oil-soluble surfactants-heptadecenyl hydroxyethyl imidazoline (HEHI), sorbitan monolaurate (Span20), didecyl phosphate (AP10), and ditridecyl hydrogen phosphate (DHP) were selected to elucidate the coupling mechanism between the dynamic micellar network structures and rheological properties. Our study establishes quantitative links between surfactant microstructure and macroscopic drag reduction. Molecular dynamics simulations show that the optimal mean square displacement for HEHI surfactant is 83 Å. Exceeding the critical micelle concentration of 250–500 ppm for HEHI negatively impacts its drag reduction efficiency. Disk rheometer experiments measured a maximum drag reduction (DR) of 17.8% at 250 ppm for HEHI, while DHP achieved 10.9% DR at 500 ppm. HEHI and Span20 buffer shear stress via hydrophobic chains. DHP and AP10 use charge repulsion to limit aggregation and sustain stable performance under high shear. All four surfactants exhibit strong shear resistance. This work demonstrates the critical role of surfactant type and concentration in oil drag reduction, revealing excellent shear resistance to guide industrial transport optimization.