The effect of added polymers on the formation of drops ejected from a nozzle

The presence of small amounts of polymer in Newtonian solvents can have a significant impact on the flow behavior of these fluids in extension-dominated flows. This study investigates the effect of elasticity on the on-demand drop formation through the use of low viscosity elastic liquids. A high-speed camera is employed to observe drops ejected from a nozzle. The drops are created using a piezoelectric sleeve that contracts around a nozzle forcing fluid out. We observe that the satellite drops commonly produced with Newtonian fluids of identical shear viscosity in the same geometry can be suppressed when polymers with sufficient molecular weight are added. For our nozzle, the minimum required molecular weight is 300k PEO at a concentration of 25 ppm. However, the resultant increased elasticity in the solution requires a greater pulse strength to eject the drop. In addition, the fluids containing polymers have a longer thread, a longer time to separation, and a lower velocity than the Newtonian fluids with similar shear viscosity. (C) 2005 American Institute of Physics.