Nonmonotonic dependence of comb polymer relaxation on branch density in semidilute solutions of linear polymers

The dynamics of branched polymers in semidilute solutions are thought to depend on a coupling between polymer chain architecture, intermolecular excluded volume interactions, and long-range hydrodynamic interactions (HI). However, it has been challenging to quantitatively understand these phenomena due to the influence of intra- and intermolecular HI and chain-chain interactions for nonlinear polymer topologies in flow. In this work, we directly observe the relaxation dynamics of comb-shaped polymers in semidilute solutions of linear polymers using single molecule experiments and molecular simulations. Experimental results are directly complemented by coarse-grained simulations of comb polymers in semidilute solutions of linear polymers including long-range HI and excluded volume interactions. Our results show an unexpected nonmonotonic dependence of comb polymer relaxation time on branch density that arises due to a subtle yet important interplay between hydrodynamic shielding and polymer architecture.