Instabilities of jets of non-Newtonian fluids impacting a plate

Abstract

The problem of buckling and coiling of jets of viscous, Newtonian liquids impacting a plate has received a substantial level of attention over the past two decades, both from experimental and theoretical points of view. Nevertheless, most industrial and everyday life fluids are non-newtonian, and their rheological properties affects their behavior in this problem. The present work aims at studying the instabilities of jets of such fluids falling on a plate, via both phenomenological descriptions and theoretical analysis of jet motion and shape. Several fluids with different rheological properties, including viscous Newtonian oil, model non-Newtonian fluids, and commercial shampoos, are used and different dynamical regimes are documented. A special focus is placed on viscoelastic, shear-thinning cetylpyridinium (CPyC1) solutions. In concentrated solutions, CPyCl surfactant molecules have been shown to assemble in long wormlike micellar structures, which gives the fluid its non-Newtonian properties. Jets of CPyCl solution show several novel shapes and dynamical regimes not observed in the case of Newtonian fluids. The present study provides quantitative experimental measurements and mechanisms for these novel features.