Origin of Tank-Treading and Breathing Dynamics of Star Polymers in Shear Flow,Macromolecules

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Origin of Tank-Treading and Breathing Dynamics of Star Polymers in Shear Flow
Macromolecules ( IF 5.1 ) Pub Date : 2020-03-30 , DOI: 10.1021/acs.macromol.9b01968
Raúl P. Peláez ₁ , Rafael Delgado-Buscalioni _{1,

2}

Affiliation

We investigate tank-treading and breathing dynamics of individual star molecules under shear flow and their relation with the macromolecule architecture. Tank-treading consists of the rotation of the arms of the star around a molecule’s center, whereas breathing consists in expansions and contractions of the whole molecule at a certain characteristic frequency. We derive scaling arguments for the trends of the frequency and decorrelation rates of both rotation and breathing modes versus the shear rate γ̇, which are supported by extensive Brownian hydrodynamics simulations. We find that breathing occurs if γ̇ is made faster than the equilibrium decorrelation rate Γ₀ of two perpendicular eigenvectors of the gyration tensor. Γ₀ increases with the star functionality, F, as Γ₀ ≈ F^0.5, which contrasts with the rotational and arm-length relaxation rates (F^–0.6 and F^–0.15 respectively). For γ̇ > Γ₀, the star becomes ellipsoidal and elongates in the flow direction and this determines the onset of the non-Newtonian regime. Remarkably, γ̇/Γ₀ provides universal trends for the shape, dynamics, and rheology of the star polymer.

中文翻译：

剪切流中星形聚合物的胎面踩踏和呼吸动力学起源

我们研究在剪切流作用下单个恒星分子的坦克踩踏和呼吸动力学及其与大分子结构的关系。踩踏运动包括恒星臂围绕一个分子中心的旋转，而呼吸则包括整个分子以某个特征频率的膨胀和收缩。我们为旋转和呼吸模式的频率和去相关速率与剪切速率γ的趋势推导了比例论证，这得到了广泛的布朗流体动力学模拟的支持。我们发现，如果γ是比平衡去相关率Γ快发生时呼吸₀旋转张量的两个垂直特征向量。Γ ₀的增加与星功能，˚F作为Γ ₀ ≈ ˚F ^0.5，其与所述旋转和臂长弛豫率（对比度˚F ^-0.6和˚F ^-0.15分别地）。对于γ>Γ ₀，星形变为椭圆形和伸长在流动方向，这确定了非牛顿制度的发作。值得注意的是，γ/Γ ₀提供普遍趋势的形状，动力学和星形聚合物的流变性。

更新日期：2020-04-24

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