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A Brownian dynamics study of the effect of self-interactions of polymers on the coil-stretch transition

It is now well known that when long chain, linear polymers in dilute solution are subjected to purely elongation flows (or elongation-dominated mixed flows), the solution properties show a sharp variation near a critical flow rate where the conformation of the polymer changes from a coiled to a stretched state or vice versa. Because the solution properties change dramatically at this so-called coil-stretch transition, it is important in many applications. The transition is primarily characterized by the critical flow rate for a given polymer molecular weight and solvent quality. While the effect of solvent quality on equilibrium properties of polymer solutions has been widely studied, there have been relatively few attempts at examining its influence on properties far from equilibrium.

We attempt to determine precisely the dependence of the critical elongational rate on solvent quality and chain length, including rigorously effects such as fluctuating hydrodynamic interactions (HI) and excluded volume (EV). A noteworthy aspect of this approach is the use of a narrow Gaussian repulsive potential, which acts pair-wise between the beads of the polymer chain. Exact results are obtained numerically using Brownian dynamics simulations, and the Successive Fine Graining (SFG) technique has been used to extrapolate the results of the bead-spring chain simulations to the limit where the number of springs approaches the number of rods in a bead rod model. The SFG technique eliminates the arbitrariness in the choice of the number of beads in the bead spring chain model.

The approach is then further extended to study the effect of solvent quality on the phenomena associated with polymer conformational hysteresis, including the nature of transition states and the activation energy for the transition.

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