Superposition rheometry of a wormlike micellar fluid
Superposition rheometry of a wormlike micellar fluid
复制标题
蠕虫状胶束流体的叠加流变测量
DOI：
10.1007/s00397-013-0718-2
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发表时间：
2013
期刊：
影响因子：
2.3
通讯作者：
J. Vermant
中科院分区：
文献类型：
--
作者：
Sunhyung Kim;J. Mewis;C. Clasen;J. Vermant
振荡测量通常用于探索材料的非线性响应，最近强烈关注使用大振幅振荡实验。然而，振荡运动叠加到稳态剪切流是一种方法，其中样品所经历的运动历史更简单。这种叠加振荡可以垂直于或平行于主流动方向施加。两种叠加的变形模式现在都可以在配有力再平衡传感器的旋转流变仪上实现，正交模式需要对法向力的控制回路进行微小修改。本文研究了蠕虫状胶束溶液的非线性性质。的Giesekus模型，这是选择它的能力来描述WLM响应和最简单的连续模型，将各向异性的微观结构的预测的结果进行比较。从均匀流态下的流体响应，可以导出速率依赖的弛豫时间和速率依赖的平台模量。后者提供了深入了解在短长度尺度流动过程中的结构各向异性，在这种情况下是各向同性的。叠加模量的进一步分析可用于分离和量化流动对链的蠕动和断裂的影响。在剪切带制度，正交模量显示出较弱的依赖于剪切速率相比，Giesekus模型的预测，但他们仍然敏感的剪切带状态的变化。
Oscillatory measurements are often used to explore the nonlinear response of materials, with recently a strong focus on using large amplitude oscillatory experiments. However, the superposition of an oscillatory motion onto a steady-state shear flow is a method where the kinematic history experienced by the sample is simpler. Such a superposed oscillation can be applied either orthogonal or parallel to the main flow direction. Both superposed deformation modes can now be achieved on rotational rheometers equipped with a force-rebalanced transducer, the orthogonal mode requiring a minor modification to the control loop of the normal force. In the present work, the nonlinear properties of a wormlike micellar (WLM) solution are studied. The results are compared with the predictions of the Giesekus model, which is chosen both for its capability to describe the WLM response and for being one of the simplest continuum models that incorporate an anisotropic microstructure. From the fluid response in the homogeneous flow regime, a rate-dependent relaxation time and a rate-dependent plateau modulus can be derived. The latter provides insight into the structural anisotropy during flow at short length scales, which in this case is isotropic. Further analysis of the superposition moduli can be used to separate and quantify the effects of flow on the reptation and breaking of the chains. In the shear-banding regime, the orthogonal moduli show a weaker dependence on shear rate compared to the predictions of the Giesekus model, yet they remain sensitive to changes in the shear-banded state.