Shear-banding and superdiffusivity in entangled polymer solutions
Shear-banding and superdiffusivity in entangled polymer solutions
复制标题
缠结聚合物溶液中的剪切带和超扩散率
DOI：
10.1103/physreve.96.062503
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发表时间：
2017
影响因子：
2.4
通讯作者：
Cheng, Xiang
中科院分区：
文献类型：
--
作者：
Shin, Seunghwan;Dorfman, Kevin D.;Cheng, Xiang
利用高分辨率共聚焦流变仪，我们研究了在大振幅振荡剪切下，在直线平面剪切池中的缠结DNA溶液的剪切剖面。随着Weissenberg数（Wi）的增加，我们观察到连续的过渡，从正常的牛顿线性剪切剖面壁滑移为主的剪切剖面，最后，剪切带剖面在高Wi。为了研究所观察到的剪切带的微观起源，我们研究了嵌入在DNA溶液中的微米级示踪剂的动力学。令人惊讶的是，在剪切框架中的示踪粒子表现出瞬态超扩散和强大的动态异质性。粒子位移的概率分布函数在大位移时遵循幂律标度，表明Lévy walk型运动，让人想起纠缠蠕虫状胶束溶液和剪切胶体玻璃中的示踪剂动力学。我们进一步表征的长度和时间尺度与示踪粒子的异常动力学。我们假设，不寻常的粒子动力学产生本地剪切诱导链解纠缠。
Using high-resolution confocal rheometry, we study the shear profiles of well-entangled DNA solutions under large-amplitude oscillatory shear in a rectilinear planar shear cell. With increasing Weissenberg number (Wi), we observe successive transitions from normal Newtonian linear shear profiles to wall-slip dominant shear profiles and, finally, to shear-banding profiles at high Wi. To investigate the microscopic origin of the observed shear banding, we study the dynamics of micron-sized tracers embedded in DNA solutions. Surprisingly, tracer particles in the shear frame exhibit transient superdiffusivity and strong dynamic heterogeneity. The probability distribution functions of particle displacements follow a power-law scaling at large displacements, indicating a Lévy-walk-type motion, reminiscent of tracer dynamics in entangled wormlike micelle solutions and sheared colloidal glasses. We further characterize the length and time scales associated with the abnormal dynamics of tracer particles. We hypothesize that the unusual particle dynamics arise from localized shear-induced chain disentanglement.