Macromolecules in Elongational Flows: Metastability and Hysteresis

Abstract

Theoretical [1–7] and experimental [8–9] investigations indicate that dilute solutions of polymers subjected to strong elongational flows undergo a transition from a state in which the macromolecules are in a relatively compact random coil configuration to one in which they are almost fully stretched. While in principle, this coil stretching transition is similar to any other phase transition (in the limit of infinite molecular weight of the polymer), it cannot be treated by the methods of equilibrium statistical mechanics [10], since a salient feature of all the experiments [8,9] is that the time spent by the polymers in the elongational flow field is comparable to their characteristic relaxation time. Thus, one is faced with an intrinsically non-equilibrium situation and in order to analyze the kinetics of the coil stretching transition, one has to rely on methods that were developed in the general context of metastability and nucleation (for systems undergoing first-order phase transitions) [11].