Dynamical and Structural Properties of Comb Long-Chain Branched Polymer in Shear Flow

Using hybrid multi-particle collision dynamics (MPCD) and a molecular dynamics (MD) method, we investigate the effect of arms and shear flow on dynamical and structural properties of the comb long-chain branched (LCB) polymer with dense arms. Firstly, we analyze dynamical properties of the LCB polymer by tracking the temporal changes on the end-to-end distance of both backbones and arms as well as the orientations of the backbone in the flow-gradient plane. Simultaneously, the rotation and tumbling behaviors with stable frequencies are observed. In other words, the LCB polymer undergoes a process of periodic stretched-folded-stretched state transition and rotation, whose period is obtained by fitting temporal changes on the orientation to a periodic function. In addition, the impact induced by random and fast motions of arms and the backbone will descend as the shear rate increases. By analyzing the period of rotation behavior of LCB polymers, we find that arms have a function in keeping the LCB polymer's motion stable. Meanwhile, we find that the rotation period of the LCB polymer is mainly determined by the conformational distribution and the non-shrinkable state of the structure along the velocity-gradient direction. Secondly, structural properties are numerically characterized by the average gyration tensor of the LCB polymer. The changes in gyration are in accordance with the LCB polymer rolling when varying the shear rate. By analyzing the alignment of the LCB polymer and comparing with its linear and star counterparts, we find that the LCB polymer with very long arms, like the corresponding linear chain, has a high speed to reach its configuration expansion limit in the flow direction. However, the comb polymer with shorter arms has stronger resistance on configuration expansion against the imposed flow field. Moreover, with increasing arm length, the comb polymer in shear flow follows change from linear-polymer-like to capsule-like behavior.

Automated summary

In this study, the effect of arms and shear flow on the dynamical and structural properties of the comb long-chain branched (LCB) polymer with dense arms was investigated using hybrid multi-particle collision dynamics (MPCD) and molecular dynamics (MD) methods. The results show that the LCB polymer undergoes periodic stretched-folded-stretched state transition and rotation, with the arms playing a role in stabilizing the polymer's motion. The impact induced by random and fast motions of arms and backbone decreases as the shear rate increases. The length of the arms and the conformational distribution are found to be important factors affecting the rotation period of the LCB polymer. The structural properties analysis reveals that the changes in gyration of the LCB polymer are in accordance with its rolling behavior, and the resistance to configuration expansion against the imposed flow field is stronger for the comb polymer with shorter arms. Additionally, with increasing arm length, the comb polymer transitions from linear-polymer-like to capsule-like behavior in shear flow.