Drag-reducing surfactant solutions in laminar and turbulent flow investigated by small-angle neutron scattering and light scattering

Abstract

Surfactant solutions containing rodlike micelles have been investigated by small angle neutron scattering and by light scattering at rest and under laminar and turbulent flow conditions. At rest and at room temperature long rods of average length 249 nm are found with static light and small angle neutron scattering. To interprete the orientation of these rods in a laminar shear gradient the a ssumption of an increased average rod length is necessary. In turbulent pipe flow the rod-like micelles are initially oriented in the bulk flow direction with more pronounced orientation in the near wall regions compared to the core regions of the pipe. Eventually a destruction of the initially rod-like micelles takes place leading to a rearrangement of the surfactant molecules into smaller aggregates part of which, in turn, build up loose but lasting (over several months at room temperature) superstructures.