Influence of polymer–surfactant aggregates on fluid flow

This paper describes the influence of interactions of poly(ethylene oxide) (PEO) with cationic cetyltrimethylammonium bromide (CTAB) micelles on drag reduction. Since the interactions between PEO and CTAB micelles alone are weak, salicylate ions were used as CTAB counterions. They facilitate formation of polymer–micelle aggregates by screening the electrostatic repulsions between the charged surfactant headgroups. The influence of polymer–surfactant interactions on drag reduction is of biomedical engineering importance. Drag reducing additives introduced to blood produce beneficial effects on blood circulation, representing a novel way to treat cardiovascular disorders. PEO is a blood-compatible polymer. However, it quickly mechanically degrades when subjected to high shear stresses. Thus, there is a need to search for other additives able to reduce drag, which would be more mechanically stable, e.g. polymer–surfactant aggregates. Numerical simulations of the flow were performed using the CFX software. Based on the internal structure of the polymer–surfactant solution, a hypothesis explaining the reason of increase of drag reduction and decrease in dynamic viscosity with increasing shear rate was proposed. It was suggested that the probable reason for the abrupt increase in friction factor, observed when the critical Reynolds number was exceeded, was the disappearance of the difference in the dynamic viscosity.

► Numerical simulations of flow of polymer–surfactant solution were performed in CFX. ► A hypothesis explaining drag reduction properties of aggregates was presented. ► Distribution of dynamic viscosity in the longitudinal section of pipe was obtained. ► The increase in shear rate causes decrease in the dynamic viscosity. ► Abrupt increase in friction factor corresponds to the constant dynamic viscosity.