Dynamics of bead formation, filament thinning and breakup in weakly viscoelastic jets

Abstract

The spatiotemporal evolution of a viscoelastic jet depends on the relative magnitude of capillary, viscous, inertial and elastic stresses. The interplay of capillary and elastic stresses leads to the formation of very thin and stable filaments between drops, or to ‘beads-on-a-string’ structure. In this paper, we show that by understanding the physical processes that control different stages of the jet evolution it is possible to extract transient extensional viscosity information even for very low viscosity and weakly elastic liquids, which is a particular challenge in using traditional rheometers. The parameter space at which a forced jet can be used as an extensional rheometer is numerically investigated by using a one-dimensional nonlinear free-surface theory for Oldroyd-B and Giesekus fluids. The results show that even when the ratio of viscous to inertio-capillary time scales (or Ohnesorge number) is as low as Oh ~ 0.02, the temporal evolution of the jet can be used to obtain elongational properties of the liquid.

Studying the effects of elongational properties on atomization of weakly viscoelastic solutions using Rayleigh Ohnesorge Jetting Extensional Rheometry (ROJER)

“…In the nonlinear region the value of strain rate experienced by the Lagrangian element reaches a plateau at✏ P = 1.1⇥10 4 s 1 which corresponds to a constant critical Weissenberg number, W i ⌘ ⌧ E✏ = 2/3. These results are in good agreement with both previous experiments and solutions/simulations in the literature for the nonlinear behavior of viscoelastic filaments during the jet breakup [33,68,70,75,76].…”

“…The appearance of large satellite droplets must be minimized in ROJER applications as they modify the desired extensional thinning kinematics. Numerical studies by Ardekani et al [76] explored nonlinear jet thinning and approach to breakup using the Giesekus constitutive equation to describe the complex fluid rheology. They showed that there is a narrow band of wavenumbers for which periodic forcing of the jet will not lead to formation of satellite droplets and this is the optimal range for elongational rheometry.…”

“…This allows us to ensure that the jet is perturbed in the vicinity of its most unstable wavelengths and a monochromatic disturbance will thus grow rapidly with time such that the nonlinear region can be repeatedly imaged with strobe illumination in a periodic manner. Experiments and computations [76] both show that viscoelastic jets tend to generate satellite droplets if the wavenumber is less than the most unstable one (i.e. kR 0  (kR 0 ) max ).…”

Solution spraying of poly(methyl methacrylate) blends to fabricate microtextured, superoleophobic surfaces

“…The filament thinning and break up of viscoelastic fluid jets are governed by different physical processes involving inertio-capillary, viscous and elastic forces. The relative importance of these forces can be determined in terms of two dimensionless parameters defined as the ratios of the time scales characterizing each process [65,66]. The Ohnesorge number (Oh) is defined as the ratio of the viscous time scale [46] and applied to the monodisperse PMMA samples dissolved in Asahiklin.…”

Instability of viscoelastic curved liquid jets with surfactants

“…The beads-on-string structure was studied by Clasen et al [9] using the Oldroyd-B model. Ardekani et al [4] investigated the dynamics of beads-on-string structure and filament thread for weakly viscoelastic jets by using the Giesekus constitutive equation and they compared the results to those of the Oldroyd-B model. Bhat et al [6] examined formation of beads-on-a-string structures and found that there are sub-satellite beads in their experiments.…”