Surface tension driven jet break up of strain-hardening polymer solutions

Experimental studies attempting to ascertain the influence of viscoelastici ty on the atomization of polymer solution are often hindered by the inabili ty to decouple the effect of shear thinning from the effect of extensional hardening. Here, the influence of viscoelasticity on the jet break up of a series of non-shear-thinning viscoelastic fluids is quantified. Previous ch aracterization using an opposed-nozzle rheometer identified the critical ex tensional rates for strain hardening of these model fluids. The strain hard ening fluids exhibit a beads-on-string structure with reduction or eliminat ion of satellite drops. Capillary instabilities grow on the filaments conne cting the spheres and eventually break the filaments up into a string of ve ry small drops about one order of magnitude smaller than the satellite drop s formed by a Newtonian fluid with the same shear viscosity, surface tensio n, and density. These results confirm that strain hardening is the key rheo logical property in jet break up and that the critical extensional rate of a fluid is pertinent in determining the final characteristics of break up. Results suggest that the opposed-nozzle rheometer does probe extensional be havior in the range of extensional rates that are relevant to jet break up, providing a tool to roughly predict jet break up. (C) 2001 Elsevier Scienc e B.V. All rights reserved.