Dual-mode draw resonance instability regulated by concentration fluctuation in the polymer solutions casting

Based on the two-fluid model, we successfully simulated the film casting process of the polymer solution system and observed the unique response wave of the film thickness and the concentration via applying perturbation. We identify that this instability pattern is essentially the product under the coupling effect of viscoelastic stress and osmotic pressure from fluctuations on different scales, which causes it to exhibit biperiodic characteristics. We call this new instability mode known as dual-mode draw resonance instability. Among them, the concentration oscillation predominates, thereby limiting the critical draw ratio Drc of the system. Through sorting out the molecular image of the polymer concentration response to perturbation, the relevant parameters are extracted, and the law of their influence on the Drc further verifies our conclusion and provides guidance for actual production.