Energetically crosslinked transient network (ECTN) model: implications in transient shear and elongation flows

Several diverse and seemingly unrelated unusual rheological phenomena such as double stress overshoots, maximum in elongation viscosity with stretch rates, phase separation in deforming solutions, uncharacteristically long restoration times, etc., observed in solutions of polar polymers might have a common physical origin, which is related to shear-induced modification of the rates of creation and loss of energetic transient crosslinks (hydrogen bonds). We argue that the dynamics of energetic crosslinks (H-bonds) are fundamentally different than those of physical crosslinks (chain entanglements). We have incorporated some of these essential differences in a phenomenological framework of a transient network theory namely the Energetically Crosslinked Transient Network (ECTN) model. We show that the ECTN model can successfully predict double stress overshoots in shear flows and the maximum in elongation viscosity with stretch rates in elongational flows.