The effects of polymer concentration and molecular weight on the breakup of laminar capillary jets

The breakup of viscoelastic jets has been investigated for a series of dilute and semidilute poly(ethylene oxide) solutions. The solvent composition was varied in order to maintain a nearly constant viscosity and surface tension for all fluids, while the apparent extensional viscosity increased with molecular weight. Photographs of the jets showed that for the fluids with low apparent extensional viscosities, the breakup length for low-velocity jets was similar to that of a Newtonian fluid with the same viscosity and surface tension. At higher velocities, a previously unreported decrease in the breakup length relative to the Newtonian fluid was observed. For the fluids with high extensional viscosities, the breakup length increased with increasing molecular weight and became independent of concentration. Satellite droplets were only suppressed in the cases where the breakup length was increased. (C) 1998 Elsevier Science B.V.