Observation of transition cascades in sheared liquid crystalline polymers
Observation of transition cascades in sheared liquid crystalline polymers
复制标题
剪切液晶聚合物中转变级联的观察
DOI：
10.1039/d0sm00275e
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发表时间：
2020
期刊：
影响因子：
3.4
通讯作者：
Dingemans, Theo J.
中科院分区：
文献类型：
--
作者：
Fox, Ryan J.;Forest, M. Gregory;Picken, Stephen J.;Dingemans, Theo J.
我们报告的剪切流变液晶溶液组成的带电，棒状聚合物，形成超分子组件分散在水中。在稳定的剪切下，我们观察到剪切增稠行为，随后是粘度的犹豫，伴随着一个非常窄的范围内的负第一法向应力差。Peclet数（Pe，剪切速率标准化杆旋转扩散）的剪切增稠的发病与以前的，高分辨率的数值模拟的Doi-Edwards-Hess动力学理论是一致的。我们询问这些动态响应通过剪切降压实验，揭示了一个复杂的演变的瞬态响应。应力瞬变的详细分析提供了令人信服的证据，即杆取向分布的主轴，方向指示器，在过渡到临界剪切速率以上的稳定流动对齐之前，经历了一系列过渡和周期性状态共存，称为皮划艇，翻滚和摇摆。
We report on the shear rheology of liquid crystalline solutions composed of charged, rodlike polymers that form supramolecular assemblies dispersed in water. Under steady shear, we observe shear thickening behavior, followed by a hesitation in the viscosity accompanied by an extremely narrow range of negative first normal stress difference. The Peclet number (Pe, shear rate normalized by rod rotational diffusivity) for the onset of shear thickening is in agreement with previous, high-resolution numerical simulations of the Doi–Edwards–Hess kinetic theory. We interrogate these dynamic responses through shear step-down experiments, revealing a complex evolution of transient responses. Detailed analysis of the stress transients provides compelling evidence that the principal axis of the rod orientational distribution, the nematic director, undergoes a cascade of transitions and coexistence of periodic states known as kayaking, tumbling, and wagging, before transitioning to steady flow alignment above a critical shear rate.