(373e) Dynamics of Semidilute Solutions of Ring/Linear Polymer Blends in Planar Extensional Flow

Semidilute polymer solution dynamics and rheology are relevant to many processing applications. Ring polymers are of particular interest due to their lack of entanglements at equilibrium. However, synthetic limitations often yield ring polymer melts and solutions which contain significant linear contaminants. Understanding the influence of blend ratio is essential, as even a small portion of linear polymers significantly alter polymer rheology. We perform Brownian dynamics simulations of ring/linear polymer solution blends at the overlap concentration varying the blend ratio from a pure ring solution to an individual ring in a linear background. We then determine the polymer dynamics and rheology at each blend ratio as a function of Wi in a planar extensional flow. We find that ring polymers unexpectedly exhibit large fluctuations in stretch. As the fraction of linear chains increases from 0% to 83%, these fluctuations grow in magnitude, whereas the dynamic behavior of the linear polymers is relatively unchanged. Our observations are consistent with single molecule experiments on DNA under comparable conditions. We explain the ring behavior by a combination of topological and hydrodynamic arguments. While transient ring-linear and ring-ring polymer hooks do form, they are relatively rare and cannot alone explain fluctuations in ring extension. We suggest that the dynamically heterogeneous concentration profile of linear vs ring polymers drive large fluctuations in the total solvent flow profile due to perturbations from polymer motions. Thus the effective flow that a ring experiences fluctuates significantly in time. Finally, we investigate the influence of concentration in relation to fundamental polymer physics concepts including hydrodynamic screening and entanglement.