Impact of Solvent Quality On the Hysteresis in the Coil-Stretch Transition of Flexible Polymers

Direct observations of long flexible biopolymers like ds-DNA in elongational flow show a coil to stretch transition (CST) and hysteresis in this transition. We examine how solvent effects alter the hysteresis of CST using Brownian Dynamics simulations. The polymer-polymer and polymer-solvent interactions are treated as an effective “solvent quality” in our implicit solvent model. The response of a molecule in flow is calculated using a dumbbell model with conformation dependent drag. A key feature of this new model is that we use a spring force relation that captures the effects of “solvent quality” on the elasticty using a simple dumbbell model. We will discuss the impact of two key parameters that affect the solvent quality: flexibility and length. Scalings have been developed to explain how the width of the hysteresis depends on these parameters. A qualitative difference is observed between the behavior of ds-DNA and ss-DNA because of their very different flexibilities.