Optical tweezers microrheology reveals the viscoelastic properties of entangled ring-linear DNA blends

Solutions of entangled polymers display complex and intriguing viscoelastic properties that are still poorly understood. While the reptation model can describe the viscoelastic properties of entangled melts of linear polymers, the model is ill-equipped to deal with circular or ring polymers, blends of polymers of varying topologies, or solutions of polymers at concentrations near the critical entanglement concentration. DNA is an excellent model system for resolving this issue as it occurs naturally in linear and circular forms. Here, we use optical tweezers microrheology to measure the linear and nonlinear viscoelastic response of semidilute and entangled blends of circular and linear DNA. We characterize the dependence of viscoelastic properties on the ratio of circular and linear chains in the blend as well as the overall solution concentration. Our results show intriguing properties of blends compared to single-component systems including increased stiffness coupled with faster relaxation rates.