Predictions for Flow Induced Changes to the Molecular Weight Distribution of Wormlike Micelles.

In practice, the microstructure of a self-assembling system is determined by its whole processing history (including deformation/flow) and not by thermodynamics alone. In some cases shear flow can promote aligned microstructures and help anneal defects, but in other cases an imposed flow will overwhelm the underlying thermodynamic forces and change the nature of the structures that have been formed. Using wormlike micelles as an example case, we build a constitutive model that accounts for (1) the kinetics of self assembly, (2) the effects of deformation, and (3) linear and non-linear stress relaxation mechanisms. When chains are deformed faster than they can naturally relax their orientation, we find that flow tends to favor increased alignment without effecting the basic microscopic structure of the micelles (e.g. their molecular weight distribution). However, when chains are deformed faster than they can relax their stretch, they tend to break and the system develops a non-equilibrium molecular weight distribution.