Nonmonotonic Stress Overshoot in Entangled Polymer Melts under Two-step Shear
简介：Shear stress overshoot in entangled polymer rheology is a hallmark of transient dynamics,but its microscopic origin remains under de-bate.Using molecular dynamics simulations,we investigate a two-step shear protocol consisting of successive startup shears separated by a wait-ing period,with the first shear interrupted before the overshoot.In the homogeneous flow,the GLaMM theory captures the stress response dur-ing the first shear,but fails to reproduce the nonmonotonic dependence of the second stress overshoot(σ2max)on the waiting time.Contrary to the prediction of a nonmonotonic normal stress component σyy during the waiting period,our simulations show that σyy,like the tube segment orientation(Sxy),the contour length of the primitive chain(L),and the entanglement number per chain(Z),relaxes monotonically toward equilib-rium.At the strain corresponding to σ2max,both the tube segment orientation and the entanglement number per chain exhibit a nonmonotonic dependence on the waiting time that closely mirrors the behavior of σ2max,indicating that both factors play significant roles in governing σ2max.Our findings are consistent with the interpretation of lanniruberto and Marrucci[ACS Macro.Lett.2014,3,552]for orientation effectsand with the viewpoint of Wang et al.[Macromolecules 2013,46,3147]for entanglement effects,although the two explanations are rooted in distinct physical pictures.These results provide new insights into the stress responses of entanglement polymer fluids and underscore the need for a more unified theoretical framework.展开
学者：Yong-JinRuanYa-QingChangJiang-YangMoBai-ChengMei
关键词：Entangled polymer rheologyMolecular dynamics simulationTube modelDisentanglement
分类号：O646(物理化学（理论化学）、化学物理学)
在线出版日期：2026-04-03 （网站首发日期）
