Ink transfer of non-Newtonian fluids from an idealized gravure cell: The effect of shear and extensional deformation

Abstract

In the presented study, we have investigated the effect of a complex flow field consisting of a combination of both shear and extensional deformation on the liquid transfer from an idealized gravure cell. The study was conducted for two classes of non-Newtonian fluid; a shear and extensional thickening nanoparticle dispersion and a extensional thickening viscoelastic polymer solution with a constant shear viscosity. The shear thickening fluid was a dispersion of fumed silica nanoparticles in polypropylene glycol and the viscoelastic fluid was a solution of polyethylene oxide (PEO) in water. The idealized gravure printing experiments were conducted using a combination of linear servo motor used to impose an extensional flow and a rotational servo motor to impose a shear flow during pickout. The fluid pickout from the gravure cell was studied as a function of the magnitude of the extensional and shear deformation rates. The fluid filament interface profile evolution during the pickout process was examined using a high speed camera. For the shear thickening fluid, the pickout resulting from a pure extensional flow field was found to be enhanced compared to Newtonian fluids at moderate velocities, resulting from the extensional thickening of the fluid. However, at large stretching velocities the pickout was found to decay dramatically due to extensional thinning of the fluid at large extension rates. The pickout behavior of the shear thickening fluid resulting from a pure shear field was found to exhibit a qualitatively similar trend to that of the extensional pickout although the pickout fraction was significantly smaller. Superposition of shear and extensional flow was found to initially improve pickout by driving the overall deformation rate higher and introducing an asymmetry in the gravure cell dewetting. At large rates, shear negatively affected pickout by causing an early onset of extensional thinning. In viscoelastic fluids, thickening of the extensional viscosity was found to enhance both the pure shear-induced pickout as well as the pure extensional-induced fluid pickout, with the shear-induced pickout relatively smaller compared to the extensional-induced pickout. For superimposed shear and extensional deformation, an enhancement in the fluid pickout was observed at certain velocity regimes, likely associated with the asymmetric dewetting from the gravure cavity wall assisted by the superimposed flows.