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

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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.