Unraveling Kinetics of Collapsed Polymers in Extensional Flow

Unraveling kinetics of collapsed polymers in relatively low strain rate extensional flow is explored via coarse-grained Brownian dynamics (BD) simulations. Unraveling probability versus the strain rate was computed for varying amounts of exposure time to flow and shown to exhibit highly non-linear behavior. For the strain rate approximately one-third of the critical strain rate, no unraveling events were observed even for the longest simulation duration explored. Statistical modeling is performed on the distribution of time of exposure to flow before polymer unraveling occurred for strain rates at which sufficient unraveling events were observed. The model thus constructed is used to evaluate unraveling kinetics for strain rates for which unraveling events are not observed in BD simulations. Results indicate a highly non-linear influence of the strain rate on the energy profile associated with the unraveling transition and this is related to the long length polymeric protrusions required to drive unraveling in such flows. As an example application of the results obtained, a quantitative prediction is made for extensional flow strain rates in which the self-associating polymeric blood protein von Willebrand Factor will exhibit pathological unraveling.