Droplet size in the breakup of a viscoelastic filament

The breakup process of a viscoelastic filament is investigated for a range of fluids with different polymer concentrations and solvent viscosities. Images taken by a high-speed camera show that the filament first thins exponentially to a terminal diameter and then generates surface waves, which form drops in a cascade manner, known as beads-on-string structures. The time spent in the exponential thinning stage is proportional to the relaxation time (λr) of the fluid, and it takes about 6λr for the tested fluids to reach the terminal diameter. The Rayleigh–Plateau instability gives reasonable prediction on the wavelength of surface waves but overestimates the growth rate. The sizes of different generations of beads are proportional to the filament diameters at which they form and can be predicted by a model based on the filament thinning rate. The bead size distribution has a Gamma distribution, and increases in polymer concentration and solvent viscosity result in a more uniform bead size distribution.