This research involves the development of numerical methods and algorithms for the study of flows of viscoelastic liquids. We use a thin-film approximation to study the formation of nanostructures following the instability and breakup of ultra-thin viscoelastic films on supporting substrates.
This work presents a study of the interfacial dynamics of thin viscoelastic films subjected to the gravitational force and substrate interactions induced by the disjoining pressure, in two spatial dimensions. The governing equation is derived as a long-wave approximation of the Navier-Stokes equations for incompressible viscoelastic liquids under the effect of gravity, with the Jeffreys model for viscoelastic stresses. For the particular cases of horizontal or inverted planes, the linear stability analysis is performed to investigate the influence of the physical parameters involved on the growth rate and length scales of instabilities. Numerical simulations of the nonlinear regime of the dewetting process are presented for the particular case of an inverted plane. Both gravity and the disjoining pressure are found to affect not only the length scale of instabilities, but also the final configuration of dewetting, by favoring the formation of satellite droplets, that are suppressed by the slippage with the solid substrate.
This work presents a novel numerical investigation of the dynamics of free-boundary flows of viscoelastic liquid membranes. The governing equation describes the balance of linear momentum, in which the stresses include the viscoelastic response to deformations of Maxwell type. A penalty method is utilized to enforce near incompressibility of the viscoelastic media, in which the penalty constant is proportional to the viscosity of the fluid. A finite element method is used, in which the slender geometry representing the liquid membrane, is discretized by linear three-node triangular elements under plane stress conditions. Two applications of interest are considered for the numerical framework provided: shear flow, and extensional flow in drawing processes.
We present a computational investigation of thin viscoelastic films and drops on a solid substrate subject to the van der Waals interaction force, in two spatial dimensions. The governing equations are obtained within a long-wave approximation of the Navier–Stokes equations with Jeffreys model for viscoelastic stresses. We investigate the effects of viscoelasticity, Newtonian viscosity, and the substrate slippage on the dynamics of thin viscoelastic films. We also study the effects of viscoelasticity on drops that spread or recede on a prewetted substrate. For dewetting films, the numerical results show the presence of multiple secondary droplets for higher values of elasticity, consistently with experimental findings. For drops, we find that elastic effects lead to deviations from the Cox–Voinov law for partially wetting fluids. In general, elastic effects enhance spreading, and suppress retraction, compared to Newtonian ones.