'Gobbling Drops': The Jetting/Dripping Transition in Flows of Polymer Solutions
by Clasen, C., Bico, J., Entov, V.M. and McKinley, G.H.
This paper discusses the breakup of capillary jets of dilute polymer solutions and the dynamics
associated with the transition from dripping to jetting. High speed digital video
imaging reveals a new scenario of transition and breakup via periodic growth and detachment
of large terminal drops. The underlying mechanism is discussed and a basic
theory for the mechanism of breakup is also presented. The dynamics of the terminal
drop growth and trajectory prove to be governed primarily by mass and momentum balances
involving capillary, gravity and inertial forces, whilst the drop detachment event
is controlled by the kinetics of the thinning process in the viscoelastic ligaments that
connect the drops. This thinning process of the ligaments that are subjected to a constant
axial force is driven by surface tension and resisted by the viscoelasticity of the
dissolved polymeric molecules. Analysis of this transition provides a new experimental
method to probe the rheological properties of solutions when minute concentrations of
macromolecules have been added.