Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, USA.
Phys Rev E. 2017 Dec;96(6-1):062503. doi: 10.1103/PhysRevE.96.062503. Epub 2017 Dec 21.
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.
利用高分辨率共焦流变仪，我们在直线平面剪切室中研究了大振幅振荡剪切下充分缠结 DNA 溶液的剪切轮廓。随着 Weissenberg 数（Wi）的增加，我们观察到从正常牛顿线性剪切轮廓到壁滑主导剪切轮廓，最后在高 Wi 下到剪切带轮廓的连续转变。为了研究观察到的剪切带的微观起源，我们研究了嵌入 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烈的动态异质性。粒子位移的概率分布函数在大位移处遵循幂律标度，表明存在 Lévy 漫步型运动，类似于缠结蠕虫状胶束溶液和剪切胶体玻璃中的示踪剂动力学。我们进一步描述了与示踪粒子异常动力学相关的长度和时间尺度。我们假设异常的粒子动力学是由局部剪切诱导的链解缠引起的。
