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首页> 外文期刊>Physics of fluids >Molecular origins of higher harmonics in large-amplitude oscillatory shear flow: Shear stress response
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Molecular origins of higher harmonics in large-amplitude oscillatory shear flow: Shear stress response

机译：大振幅振荡剪切流中高次谐波的分子起源：剪切应力响应

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Recent work has focused on deepening our understanding of the molecular origins of the higher harmonics that arise in the shear stress response of polymeric liquids in large-amplitude oscillatory shear flow. For instance, these higher harmonics have been explained by just considering the orientation distribution of rigid dumbbells suspended in a Newtonian solvent. These dumbbells, when in dilute suspension, form the simplest relevant molecular model of polymer viscoelasticity, and this model specifically neglects interactions between the polymer molecules [R. B. Bird et al., "Dilute rigid dumbbell suspensions in large-amplitude oscillatory shear flow: Shear stress response," J. Chem. Phys. 140, 074904 (2014)]. In this paper, we explore these interactions by examining the Curtiss-Bird model, a kinetic molecular theory designed specifically to account for the restricted motions that arise when polymer chains are concentrated, thus interacting and specifically, entangled. We begin our comparison using a heretofore ignored explicit analytical solution [X.-J. Fan and R. B. Bird, "A kinetic theory for polymer melts. VI. Calculation of additional material functions," J. Non-Newtonian Fluid Mech. 15, 341 (1984)]. For concentrated systems, the chain motion transverse to the chain axis is more restricted than along the axis. This anisotropy is described by the link tension coefficient,., for which several special cases arise: epsilon = 0 corresponds to reptation, epsilon > 1/8 to rod-climbing, 1/5 <= epsilon <= 3/4 to reasonable predictions for shear-thinning in steady simple shear flow, and epsilon = 1 to the dilute solution without hydrodynamic interaction. In this paper, we examine the shapes of the shear stress versus shear rate loops for the special cases epsilon = (0, 1/8, 3/8, 1), and we compare these with those of rigid dumbbell and reptation model predictions. Published by AIP Publishing.
机译：最近的工作集中在加深我们对在大振幅振荡剪切流中聚合物液体的剪切应力响应中产生的高次谐波的分子起源的理解。例如，仅考虑悬浮在牛顿溶剂中的刚性哑铃的取向分布就可以解释这些高次谐波。这些哑铃在稀释的悬浮液中时，形成了聚合物粘弹性的最简单的相关分子模型，而该模型专门忽略了聚合物分子之间的相互作用。 B. Bird等人，“在大振幅振荡剪切流中稀释刚性哑铃悬架：剪切应力响应”，《化学学报》。物理140，074904（2014）]。在本文中，我们通过检查Curtiss-Bird模型来探索这些相互作用，该模型是专门设计用于解决聚合物链浓缩，相互作用和纠缠在一起时出现的受限运动的动力学分子理论。我们使用迄今为止被忽略的显式解析解[X.-J. Fan和R. B. Bird，“聚合物熔体动力学理论。VI。附加材料功能的计算”，J。非牛顿流体力学。 15，341（1984）]。对于集中系统，横向于链条轴线的链条运动比沿轴线的运动受到更大的限制。这种各向异性由链条张力系数来描述，在这种情况下会出现几种特殊情况：epsilon = 0对应于重复; epsilon> 1/8对应于爬杆; 1/5 <= epsilon <= 3/4对应于合理的预测在稳定的简单剪切流中剪切稀化，ε= 1到没有水动力相互作用的稀溶液中。在本文中，我们检查了特殊情况下ε=（0，1/8，3/8，1）的剪切应力与剪切速率环的形状，并将其与刚性哑铃和蠕动模型的预测进行了比较。由AIP Publishing发布。

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