Viscoelastic Jets

We study the problem of a liquid poured out of an orifice at a given height and speed that hits a solid surface. Everybody has experienced such a situation, for example by dropping honey onto a bread slice, or pouring shower gel onto one's hand. Honey is a purely viscous, newtonian fluid: the jet thins continuously and coils regularly. Newtonian fluids in this situation (a) have been well studied, but we add another level of complexity by studying viscoelastic jets.

Our main non-Newtonian fluid is a concentration cetylpyridinium chloride (CPyCl) wormlike micellar solutions. Jets of this fluid show novel behaviors: the jet widens at its base (reverse swell phenomenon) and folds back and forth on itself (b). Both are a result of the interplay of non-Newtonian properties (viscoelasticity, shear-thinning) with gravitational, viscous, and inertial effects in the jets.

We have mapped the jetting behaviors in the parameter space, composed of the height of fall, the flow rate, the viscosity and elasticity of the fluid - or the dimensionless numbers made out of their combinations. In addition, we have provided rationales for the transitions between the regimes, as well as predictions for the dependencies with the various parameters of folding amplitude and frequency and the amount of reverse swell.

Jets of some shampoos show another behavior, the leaping shampoo or Kaye effect (c). The jet bends and slides on the top of a mound of liquid, jumping as high as 5cm for a jet radius of 1mm!

Future works include broadenning the range of non-Newtonian fluids used and using an enclosure to control the temperature and humidity of the surrounding air, allowing the study of the largest heights of fall.