Title: 
Highly Entangled Wormlike Micellar Solutions - Model and Predictions  
in LAOS and Extensional Flows

Abstract:
Surfactant molecules (micelles) can self-assemble in solution into  
long flexible structures known as wormlike micelles. These structures  
entangle, forming a dense network and thus exhibit viscoelastic  
effects, similar to entangled polymer melts & solutions. However, in  
contrast to polymeric networks, wormlike micelles break and reform  
leading to a new relaxation mechanism. Steady shearing flows of these  
solutions exhibit spatial inhomogeneities such as 'shear-bands'  
during deformation which have been well-studied both experimentally  
and theoretically.   In this talk the dynamical response of two  
recently formulated constitutive models (denoted respectively VCM, PEC 
+M) under Large Amplitude Oscillatory Shear (LAOS) and strong  
extensional deformations will be presented.  In LAOS, kinematic  
inhomogeneities develop across the gap for a wide range of strains  
and frequencies.The complex dynamics of shear-banding in this  
unsteady large amplitude deformation can be conveniently represented  
using a Pipkin diagram.  In filament stretching experiments with  
these wormlike micellar solutions it has been  observed that the  
elongating fluid filaments can experience a sudden rupture near the  
midplane at high strain rates [Rothstein]. This newly observed  
failure mechanism is not related to the visco-capillary thinning  
observed in viscous Newtonian fluids, but is conjectured to be due to  
a viscoelastic cohesive failure event. The dynamics of the new VCM  
model in transient uniaxial elongation are examined to aid in further  
understanding this elongational rupturing mechanism.