Characterizing the Microscale Mobility and Viscoelasticity of Entangled Blends of DNA of Varying Lengths and Topologies*

Due to the complexity of entangled polymer systems, the majority of previous studies have focused on monodisperse systems of linear polymers. However, systems that exhibit the most intriguing and useful properties – those that make up biological cells and fluids and are used to develop new materials – are blends of polymers of different lengths or topologies.
To elucidate the viscoelastic properties of entangled polymer blends, we use DNA as a model polymer system that naturally occurs in ring and linear form with wide-ranging lengths. We use particle-tracking microrheology to characterize the viscoelastic properties of entangled blends of: (1) 45 kbp linear and ring DNA and (2) 11 kbp and 111 kbp linear DNA. Specifically, we track the brownian motion of embedded microspheres to quantify the diffusive characteristics and viscoelastic moduli of blends. We systematically determine the dependence of these properties on the ratio of the two different blend species ((1) ring vs linear and (2) short vs long). Results of our systematic study shed new light on a currently intractable problem in polymer physics, and provide design principles for engineering new biopolymeric materials.