Nonequilibrium thermodynamic investigation of the shear banding phenomenon in entangled polyacrylamide solutions

当软材料（复杂流体）受到强烈的剪切变形时，这些材料可以形成具有不同剪切速率和/或浓度的局部带，称为剪切带。有人假设，剪切带是由扩散引起的聚合物溶液。最近，我们开发了一个热力学聚合物模型，考虑到Fickian扩散和应力诱导迁移。在这个模型中，它是假设在浓度和应力的局部梯度产生的聚合物成分和溶剂之间的非平凡的速度差。该模型的优点是将微分速度作为状态变量。由导数扩散项的存在而产生的额外边界条件可以直接施加到这个变量上。因此，不再需要微观结构信息，而是模型的结果。本项目的目标是使用数值和实验相结合的方法来验证上述假设。该模型将在两个基准流（平面通道和收缩流）进行系统的研究。通过与测速仪、荧光快照和中子散射实验进行比较，验证了计算结果。可靠的聚合物模型的开发对于塑料制造和其他行业（如食品和制药行业）非常重要，因为它们的未来应用将允许更好地设计产品和工业流程的纹理特性。

When soft materials (complex fluids) are subject to strong shear deformations, these materials can develop localized bands with different shear rates and/or concentrations, known as shear bands. It has been hypothesized that shear banding is caused in polymeric solutions by diffusion. Recently, we developed a thermodynamic polymer model taking into account Fickian diffusion and stress-induced migration. In this model, it is assumed that local gradients in concentration and stress generate a nontrivial velocity difference between the polymeric constituents and the solvent. The advantage of this model is that the differential velocity is treated as state variable. The extra boundary conditions arising from the presence of derivative diffusive terms can be directly imposed with respect to this variable. Microstructural information is therefore not anymore required but is rather an outcome of the model. The goal of this project is to verify the above-mentioned hypothesis using a combined numerical and experimental approach. The model will be systematically studied in two benchmark flows (planar channel and contraction flows). The computations will be validated by performing a comparison with velocimetry, fluorescence snapshot, and neutron scattering experiments. The development of reliable polymer models is of importance to plastics manufacturing and other sectors like the food and pharmaceutical industries as their future application will allow to better design the textural properties of products and industrial flow processes.