Rheological and structural properties of associated polymer networks studied: Via non-equilibrium molecular dynamics simulation

An intensive understanding of the rheological and structural properties of polymer physical networks formed via associative functional groups of chain ends at the molecular level is still lacking. Herein, we employed coarse-grained non-equilibrium molecular dynamics (NEMD) simulation to explore the shear effect on this particular system. Firstly, we reproduced the shear thinning behavior of pure linear polymer chains. It was also found that the shear thinning behavior weakens and the corresponding zero-shear viscosity decreases for short polymer chains. Then we tailored the physical polymer network by varying the interaction strength between the end functional groups, and a prominent shear thinning behavior also occurs, attributed to the breakage of the physical network resulting from the chain alignment and orientation induced by the shear, and the physical network shows better integrity as the interaction strength between ending beads increases. Finally, we constructed end-functionalized polymer systems with bimodal molecular weight distribution, which showed that the shear viscosity and shear stress decrease with the proportion of the long chain, while the degree of the shear thinning is independent of it. At the same time, a large shearing force will destroy part of the physical network, but a small shear rate promotes the formation of the physical network. Generally, our simulated results may provide a molecular-level understanding of the structural and rheological properties of associated and bimodal molecular weight distribution polymers, as well as achieve efficient guidance for their molecular design and processing.