Macroscopic Response of Wormlike Micelles to Elongational Flow

Opposed nozzle flow is used to measure the elongational properties of wormlike micelles. Well-characterized semidilute micellar solutions of CPCl/Sal in concentrated brine are used. By varying temperature and concentration, the viscoelastic properties (τ<INF>R</INF>, G<INF>0</INF>) of the equilibrium solutions can be controlled and the influence of viscoelasticity on elongational viscosity probed. Results indicate three regimes of steady elongational behavior:  a constant viscosity at low elongational rates, an increase to a maximum viscosity, and then a subsequent drop in viscosity. Scaling of the macroscopic elongational properties with linear viscoelastic parameters and similarities between these solutions and entangled polymer solutions indicate that semidilute CPCl/Sal solutions do not exhibit significant changes in micellar structure and may provide model systems for studying the influence of complex flow fields on entangled polymer solutions.