Modeling of interfacial diffusion in adjacent flows of polymer films

Adjacent flow of two polymeric fluids occurs in many industrial processes. Under these processes, entangled polymer chains usually undergo extensional flow and shear flow deformation fields, rendering orientation and stretching within polymer chains. In the present paper, the chain stretching ratio and interfacial diffusion in a symmetric bilayer film in the isothermal adjacent flows in a coextrusion process are modeled using the double constraint release with chain stretching model. Extension-dominant and shear-dominant flows are considered separately for ease of the modeling process. Also, the impact of entanglement density on the reptation relaxation is investigated to determine the entanglement density variation and its effect on the stretching ratios and interfacial diffusion. Our findings show that extension-dominant and shear-dominant deformation fields have different impacts on polymer chain stretching, affecting polymer interfacial chain diffusion. Our findings show that while shear flow with the strength of 30 s−1 increases the stretching ratio by 28%, extensional flow with the same strength increases the stretching ratio by 60% of the maximum stretching ratio for polystyrene chains with an average molecular weight of 200 km/mol at 175 °C. Our results show that initial entanglement density is effective on the chain stretching only in the transition step before chains reach equilibriums. This study highlights the impact of flow conditions and chain configuration in polymers on engineering the diffusion of polymer chains at the interface of layered configurations.