Effect of fluid relaxation time of dilute polymer solutions on jet breakup due to a forced disturbance

In inertia-dominated breakup of a low-viscosity liquid jet, complex disintegration mechanisms lead to a polydisperse distribution of the sizes of droplets formed. Macromolecules in solution increase the extensional viscosity and suppress the formation of satellite drops. Large extensional stresses lead to, and prevent, viscoelastic filaments from breaking up beads-on-string structure). The drainage rate of fluid from the filaments into the beads is constant and can be used to estimate the relaxation time of the fluid. The nature of capillary breakup due to an imposed disturbance is investigated as a function of disturbance wavelength-to-diameter ratio and initial disturbance amplitude. We identify the key dynamics of the process and its relation to the fluid relaxation time; this allows us to control satellite drop formation. There is a minimum fluid relaxation time for suppression of satellite drops. Above this relaxation time, suppression of satellite drops is a function of the disturbance parameters. The results identify the fluid relaxation time and the time scale of the disturbance growth as the relevant time scales in capillary breakup of viscoelastic fluids. Through this study, we demonstrate that the drop size distribution from capillary breakup of polymer solutions can be controlled through choice of molecular weight of the polymer. (C) 2002 The Society of Rheology.