Wave behavior in the coating process of multilayer polymeric materials

A mathematical analysis model of multilayer viscoelastic fluids flowing down an inclined plane for any arbitrary wave numbers has been established to improve multilayer product quality in the coating processes. In the stability study of the free surface with small elastic force, Reynolds number is the primary parameter to induce surface instability for long and intermediate waves. When the elastic force in either layer is large, elasticity can affect the stability of long and intermediate waves. In addition, viscosity stratification across the interface can also affect the stability of the free surface. For the interfacial stability of two-layer flow system, it is found that purely elastic instability occurs in most depth ratios for the whole spectrum of waves when the fluid with elasticity is placed as the inner layer next to the solid wall. In the study of stability for viscoelastic fluid it demonstrates that arranging the more elastic and less viscous fluid as the outer layer leads to interfacial stability. In the more than three-layers investigation we found that placing the most viscous and least elastic liquid as the innermost layer next to the solid wall and the least viscous and most elastic liquid as the outermost layer next to the passive air can ensure the stability for the whole spectrum of waves.