Evaluation of constitutive models for shear-banding wormlike micellar solutions in simple and complex flows
Evaluation of constitutive models for shear-banding wormlike micellar solutions in simple and complex flows
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DOI：
10.1016/j.jnnfm.2022.104855
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发表时间：
2022-07-01
影响因子：
3.1
通讯作者：
Shen, Amy Q.
中科院分区：
文献类型：
--
作者：
Varchanis, Stylianos;Haward, Simon J.;Shen, Amy Q.
蠕虫状胶束溶液具有复杂的流变性：当暴露于流场时，蠕虫状胶束可以定向、拉伸并破裂成更小的胶束。缠结蠕虫状胶束溶液表现出剪切带特征：具有不同局部粘度的宏观条带沿速度梯度方向沿着排列和堆叠，导致简单剪切下的非单调流动曲线。我们对四种常用的本构模型进行了系统分析，这些模型可以预测非单调流动曲线，并可能描述具有剪切带特征的缠结蠕虫状胶束溶液的流变学：Johnson-Segalman模型、Giesekus模型、触变粘弹模型和Vasquez-Cook-麦金利（VCM）模型。所有四个本构模型包含一个应力扩散项，考虑剪切带之间的平滑过渡，并确保数值解的唯一性。首先，模型拟合剪切和拉伸实验数据的剪切带蠕虫状胶束溶液。随后，他们被用来解决三个非均匀流：Poiffille流在一个平面通道中，在一个十字槽几何形状的流动，并通过一个圆柱体在一个直通道中的流动。这些流动中的每一个都将蠕虫状胶束溶液暴露于不同的流动运动学（剪切、拉伸和混合），揭示了其流变响应的不同方面。每个模型的预测能力进行评估，通过直接比较的数值结果，以前公布的实验数据从微流体装置与相应的流动配置。虽然所有的模型都可以定性地描述在基准流中实验观察到的特征，如塞状速度分布和弹性不稳定性，但它们都没有产生定量的一致性。基于模型的整体性能，并考虑到其不同的数值复杂性，我们得出结论，Giesekus模型是目前最合适的本构方程模拟剪切带蠕虫状胶束溶液中的流动，表现出剪切和拉伸变形。然而，蠕虫状胶束溶液的模型预测和实验之间的定量不匹配的要求，改进的本构模型，在未来的工作中开发。
Wormlike micellar solutions possess complex rheology: when exposed to a flow field, the wormlike micelles may orientate, stretch, and break into smaller micelles. Entangled wormlike micellar solutions exhibit shear banding characteristics: macroscopic bands with different local viscosities are organized and stacked along the velocity gradient direction, leading to a non-monotonic flow curve in simple shear. We present a systematic analysis of four commonly used constitutive models that can predict a non-monotonic flow curve and potentially describe the rheology of entangled wormlike micellar solutions with shear-banding characteristics: the Johnson-Segalman, the Giesekus, the thixotropic viscoelastic, and the Vasquez-Cook-McKinley (VCM) models. All four constitutive models contain a stress diffusion term, to account for a smooth transition between the shear bands and ensure a uniqueness of the numerical solution. Initially, the models are fitted to shear and extensional experimental data of a shear-banding wormlike micellar solution. Subsequently, they are employed to solve three non-homogeneous flows: the Poiseuille flow in a planar channel, the flow in a cross-slot geometry, and the flow past a cylinder in a straight channel. Each of these flows exposes the wormlike micellar solution to different flow kinematics (shear, extensional, and mixed), revealing different aspects of its rheological response. The predictive capability of each model is evaluated by directly comparing the numerical results to previously published experimental data obtained from microfluidic devices with corresponding flow configurations. While all the models can describe qualitatively the characteristic features observed experimentally in the benchmark flows, such as plug-like velocity profiles and elastic instabilities, none of them yields a quantitative agreement. Based on the overall performance of the models and also accounting for their differing numerical complexity, we conclude that the Giesekus model is at present the most suitable constitutive equation for simulating shear banding wormlike micellar solutions in flows that exhibit both shear and extensional deformations. However, the quantitative mismatch between model predictions and experiments with wormlike micellar solutions demand that improved constitutive models be developed in future works.