Polymer Conformational Hysteresis in Mixed Flows

We aim to study the non equilibrium behavior of polymer molecules in flows of dilute solution. It has been shown that polymers undergo a coil-to-stretch transition (unraveling) in extensional flow. In addition, this transition exhibits a hysteresis; that is, both the coiled state and the extended state can co-exist at the same flow strength, depending on initial conditions. This transition can be analyzed as a pseudo first order phase transition by calculating an effective energy barrier between the two states, and the rate of state hopping can be obtained. We wish to develop a rate theory for the coil to stretch transition in more general mixed (extensional + vortical) flows and analyze the effective conformational energy barrier as a function of flow mixedness. To accomplish this task, we are performing Brownian dynamics computer simulations coupled with single molecule fluorescence experiments using DNA as a model polymer. These BD simulations are able to capture essential polymer dynamics, including hydrodynamic interactions and the coil-to-stretch hysteresis.