Temporary degradation and recovery of drag-reducing surfactant solutions

We have investigated the intentional temporary degradation and the subsequent recovery of the drag-reducing properties of surfactant solutions. Degradation was achieved by exposing the fluid to mechanical stresses after which it showed significantly reduced drag reduction capability. The recovery time varies from a fraction of second to several minutes, depending on the surfactant concentration, the counter-ion concentration and the temperature. The recovery process generally showed a linear increase of the drag reduction level with time, with the rate of recovery being essentially independent of the flow velocity and the initial level of degradation, though the recovery at rest is considerably slower than the recovery under turbulent flow conditions. The recovery time decreases sharply with increasing concentration and temperature, and with increasing counter-ion concentration for the cationic surfactant. The mechanical degradation apparently affects not only the shear-induced structure but also the rod-like micelles themselves.