  Wormlike micellar solutions formed by long-chained zwitterionic surfactants
show gel-like rheology at room temperature and have recently been found to
exhibit other complex and interesting rheological features. We study the
dynamics of these wormlike micellar gels in a pipe-flow scenario using optical
coherence tomography-based velocimetry and report the existence of plug flows
with strong wall slip and non-parabolic velocity profiles for different
surfactant concentrations and imposed flow rates. We rationalize these results
as features of a developing transient flow of a viscoelastic solution in space
and time and show that these shear layers indicate a flow induced
heterogeneity. Our experiments shed light on the transient fluid dynamics of
wormlike micelles in simple geometries and highlight the complexity of flows
involving wormlike micellar gels and similar soft matter systems in canonical
flows.
