Nonequilibrium Behaviors of Entangled Diblock Copolymers at the Entangled Polymer-Polymer Interface under Steady Shear Flow.

The slip phenomena and the individual configuration dynamics of interfacial copolymer chains in the entangled polymer-polymer interface under fast shear flow are analyzed using mDPD simulations on ternary blends of A125/B125/C125D125 with different incompatibilities or interface strengths. We observe two distinct power-law regions of slip velocity against interfacial shear stress: from Vs ∼ σ5 to Vs ∼ σ1 at an increasing shear rate with the interface strength. At the micro level, the two regions correspond to the integrated and incomplete interfacial entanglement network with the shear-induced disentanglement of interfacial chains, respectively. For the individual chain dynamics of interfacial copolymers, we clarify that for the weak incompatibility, the tumbling event of interfacial copolymer chains is irregular and occasional and includes six processes: align and flip, collapse, tumble, stretch, reflip, and recoil and tumble. For the system with strong incompatibility, the interfacial copolymer chain undergoes the stretched-coil conformational transition via elastic retraction. As the interfacial entanglement network disintegrates, the hairpin-like configuration is dominant during the tumbling motion or elastic retraction of the interfacial copolymer chain.

Non-Rouse behavior of short ring polymers in melts by molecular dynamics simulations.

Short ring polymers are expected to behave nearly Rouse-like due to the little effect of topological constraints of non-knot and non-concatenation. However, this notion is questioned because of several simulation and experiment findings in recent times, which requires a further more quantitative study. Therefore, we perform a deep investigation of statics and dynamics of flexible short ring polymers (N < 2Ne) in melts via molecular dynamics simulations by further taking linear analogues as well as all-crossing ring and linear polymers with switched off topological constraints for comparisons and demonstrate the noticeable deviations from the Rouse model in terms of local and global scales. Although the overall size is compact, the subchains are swollen, which is traced back to the deeper "segmental correlation hole" effect. The same scaling relationship of the non-Gaussian deviation of the static structure factor holds, but the deviation magnitude of rings is larger than that of linear analogues. By checking the non-Gaussian parameter and autocorrelation function of center-of-mass velocity, the physical origin of anomalous sub-diffusions of short rings is identified as unscreened viscoelastic hydrodynamic interactions and not correlation hole effects, like linear analogues.