Effect of aspect ratio and fluid elasticity on chain orientation in isothermal film casting process

The characteristics of extensional flow and the chain orientations of the isothermal film casting process utilizing a two-dimensional (2-D) viscoelastic model with finite element methods (FEM) were studied. Steady state and transient solutions were obtained for a relatively large aspect ratio regime by employing successive iterative schemes. In this work, higher aspect ratios of the equipment caused highly oriented molecular structures because the aspect ratio increases as the flow changes from planar to uniaxial extensional flow. Fluid viscoelasticity always alleviated the neckin phenomenon and led to the planar extension regime even if dichotomous behavior was observed for draw resonance in extensional thickening and thinning fluids. Consequently, the change in the characteristic of extensional deformation from uniaxial deformation to the planar extension deteriorated the molecular orientation.