In some recent experiments on entangled polymers of stress growth in the startup of fast shear flows, an undershoot in the shear stress is observed following the overshoot, i.e., before approaching the steady state. Whereas tumbling of the entangled chain was proposed to be at its origin, here, we investigate another possible cause for the stress undershoot, i.e., slippage at the interface between the polymer and solid wall. To this end, we extend the primitive chain network model to include slip at the interface between entangled polymeric liquids and solid walls with grafted polymers. We determine the slip velocity at the wall, and the shear rate in the bulk, by imposing that the shear stress in the bulk polymers is equal to that resulting from the polymers grafted at the wall. After confirming that the predicted results for the steady state are reasonable, we examine the transient behavior. The simulations confirm that slippage weakens the magnitude of the stress overshoot, as reported earlier. The undershoot is also weakened, or even disappears, because of a reduced coherence in molecular tumbling. Disentanglement of grafted chains from bulk ones, taking place throughout the stress overshoot region, does not contribute to the stress undershoot.

中文翻译：

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缠结聚合物剪切启动的原始链网络模拟中的壁滑及其对剪切应力下冲的影响

在一些有关快速剪切流开始时应力增长的纠缠聚合物的最新实验中，在过冲之后，即在接近稳态之前，观察到剪切应力的下冲。尽管缠结链的翻转被认为是其起源，但在这里，我们研究了应力下冲的另一种可能原因，即在聚合物和固体壁之间的界面处打滑。为此，我们扩展了原始链网络模型，以包括在纠缠的聚合物液体和带有接枝聚合物的固体壁之间的界面处的滑移。通过强加在散装聚合物中的剪切应力等于在壁处接枝的聚合物所产生的剪切应力，我们确定了在壁上的滑移速度以及在整体中的剪切速率。在确认稳态的预测结果合理之后，我们检查了瞬态行为。仿真证实，滑移会削弱应力超调的幅度，如先前报道。由于分子翻转的相干性降低，下冲也被削弱，甚至消失。在整个应力超调区域发生的接枝链与散装链的脱开，不会导致应力下冲。