Nonlinear Microrheology Reveals Entanglement-Driven Molecular-Level Viscoelasticity of Concentrated DNA

We optically drive a trapped microscale probe through entangled DNA at rates up to 100x the disentanglement rate (Wi approximate to 100), then remove the trap and track subsequent probe recoil motion. We identify a unique crossover to the nonlinear regime at Wi approximate to 20. Recoil dynamics display rate-dependent dilation and complex power-law healing of the reptation tube. The force response during strain exhibits key nonlinear features such as shear thinning and yielding with power-law rate dependence. Our results, distinctly nonclassical and in accord with recent theoretical predictions, reveal molecular dynamics governed by individual stress-dependent entanglements rather than chain stretching.