ENERGETICALLY CROSS-LINKED 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, uncharacteris tically long restoration times, etc., observed in solutions of polar p olymers might have a common physical origin, which is related to shear -induced modification of the rates of creation and loss of energetic t ransient crosslinks (hydrogen bonds). We argue that the dynamics of en ergetic 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 tr ansient network theory namely the Energetically Crosslinked Transient Network (ECTN) model. We show that the ECTN model can successfully pre dict double stress overshoots in shear flows and the maximum in elonga tion viscosity with stretch rates in elongational flows. (C) 1998 Else vier Science B.V.