Transient shear banding in entangled polymers: A study using the Rolie-Poly model
Transient shear banding in entangled polymers: A study using the Rolie-Poly model
复制标题
DOI：
10.1122/1.3610169
复制
发表时间：
2011-09-01
影响因子：
3.3
通讯作者：
Olmsted, P. D.
中科院分区：
文献类型：
--
作者：
Adams, J. M.;Fielding, S. M.;Olmsted, P. D.
空间不均匀的剪切流发生在缠结的聚合物溶液，无论是作为稳态剪切带和瞬态后，一个大的步骤应变或在启动过程中，以稳定的均匀剪切速率。从理论上讲，稳态剪切带是一个标志性的模型与总剪切应力和施加的剪切速率之间的非单调本构关系，但瞬态条带有时会出现在流体中，不剪切带在稳态。我们使用扩散的Rolie-Poly模型在牛顿溶剂中模拟这种行为，其稳态本构行为可以是单调的或非单调的，这取决于对流约束释放的程度。我们研究单调稳态本构行为。线性稳定性分析的启动到足够高的剪切速率表明，空间波动是不稳定的，在早期。这种不稳定性和（随时间变化的）本构曲线的负斜率之间存在很强的相关性。如果最不稳定特征值的时间积分足够大，则系统会出现瞬态剪切带，随后在稳态时消失。我们如何扰动，由于波动或不均匀的应力，可以触发这种不稳定性。这种瞬态行为与最近在缠结聚合物溶液中的观察结果相似。(c)2011流变学学会。[DOI 10.1122/1.3610169]
Spatially inhomogeneous shear flow occurs in entangled polymer solutions, both as steady state shear banding and transiently after a large step strain or during startup to a steady uniform shear rate. Theoretically, steady state shear banding is a hallmark of models with a nonmonotonic constitutive relation between total shear stress and applied shear rate, but transient banding is sometimes seen in fluids that do not shear band at steady state. We model this behavior using the diffusive Rolie-Poly model in a Newtonian solvent, whose steady state constitutive behavior can be monotonic or nonmonotonic depending on the degree of convective constraint release. We study monotonic steady state constitutive behavior. Linear stability analysis of the startup to a sufficiently high shear rate shows that spatial fluctuations are unstable at early times. There is a strong correlation between this instability and the negative slope of the (time dependent) constitutive curve. If the time integral of the most unstable eigenvalue is sufficiently large, then the system exhibits transient shear bands that later vanish in steady state. We show how perturbations, due to fluctuations or the inhomogeneous stresses, can trigger this instability. This transient behavior is similar to recent observations in entangled polymer solutions. (c) 2011 The Society of Rheology. [DOI: 10.1122/1.3610169]