  We present a reformulation of the 'reactive rod model' (RRM) of Dutta and
Graham [Dutta, Sarit and Graham, Michael D., JNNFM 251 (2018)], a constitutive
model for describing the behavior of dilute wormlike micelle solutions. The RRM
treats wormlike micelle solutions as dilute suspensions of rigid Brownian rods
undergoing reversible scission and growth in flow. Evolution equations for
micelle orientation and stress contribution are coupled to a kinetic reaction
equation for a collective micelle length, producing dynamic variations in the
length and rotational diffusivity of the rods. This model has previously shown
success in capturing many critical steady-state rheological features of dilute
wormlike micelle solutions, particularly shear-thickening and -thinning,
non-zero normal stress differences, and a reentrant shear stress-shear rate
curve, and could fit a variety of steady state experimental data. The present
work improves on this framework, which showed difficulty in capturing transient
dynamics and high-shear behavior, by reformulating the kinetic equation for
micelle growth on a more microstructural (though still highly idealized) basis.
In particular, we allow for micelle growth associated with strong alignment of
rods and breakage due to tensile stresses along the micelles. This new
formulation captures both steady and transient shear rheology in good agreement
with experiments. We also find good agreement with available steady state
extensional rheology.
