Microstructural evolution of a model, shear-banding micellar solution during shear startup and cessation.
Microstructural evolution of a model, shear-banding micellar solution during shear startup and cessation.
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剪切带胶束溶液模型在剪切启动和停止过程中的微观结构演化。
DOI：
10.1103/physreve.89.042301
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发表时间：
2014
期刊：
影响因子：
--
通讯作者：
N. Wagner
中科院分区：
文献类型：
--
作者：
C. López‐Barrón;A. Gurnon;A. Eberle;L. Porcar;N. Wagner
我们提出了直接测量的发展过程中的流动启动和停止在平面上的流动的稳定的剪切带聚合物胶束溶液的段级微观结构。这些测量提供了一个明确的，定量的微观结构的理解流动启动过程中观察到的阶段：一个初始的弹性响应与有限的对齐，产生一个大的应力过冲到一个均匀的流与相关的胶束对齐，持续约三个弛豫时间。这种瞬态之后是一个剪切（扭结）带形成与流动对齐的低粘度带，表现出剪切诱导的浓度波动和共存的几乎各向同性带的均匀，高粘弹性胶束溶液。只有在大约两次爬行后才能达到稳定的带状流动。流动停止从这个剪切带状态也被发现是不平凡的，表现出一个初始的快速松弛，只有轻微的结构松弛，其次是一个较慢的松弛与平衡流体的特征松弛时间的排列胶束流体。这些测量解决了文献中围绕缠结蠕虫状胶束中剪切带机制的争议，并通过与现有文献的比较，进一步深入了解了相关系统中驱动剪切带不稳定性的机制。所描述的方法和仪器应该在探索复杂的流体流变学和测试基于微观结构的本构方程中找到广泛的用途。
We present direct measurements of the evolution of the segmental-level microstructure of a stable shear-banding polymerlike micelle solution during flow startup and cessation in the plane of flow. These measurements provide a definitive, quantitative microstructural understanding of the stages observed during flow startup: an initial elastic response with limited alignment that yields with a large stress overshoot to a homogeneous flow with associated micellar alignment that persists for approximately three relaxation times. This transient is followed by a shear (kink) band formation with a flow-aligned low-viscosity band that exhibits shear-induced concentration fluctuations and coexists with a nearly isotropic band of homogenous, highly viscoelastic micellar solution. Stable, steady banding flow is achieved only after approximately two reptation times. Flow cessation from this shear-banded state is also found to be nontrivial, exhibiting an initial fast relaxation with only minor structural relaxation, followed by a slower relaxation of the aligned micellar fluid with the equilibrium fluid's characteristic relaxation time. These measurements resolve a controversy in the literature surrounding the mechanism of shear banding in entangled wormlike micelles and, by means of comparison to existing literature, provide further insights into the mechanisms driving shear-banding instabilities in related systems. The methods and instrumentation described should find broad use in exploring complex fluid rheology and testing microstructure-based constitutive equations.