Oscillatory Motion of Viscoelastic Drops on Slippery Lubricated Surfaces

Abstract The introduction of slippery lubricated surfaces allows the investigation of the flow of highly viscous solutions which otherwise will hardly move on standard solid surfaces. Here we present the study of the gravity induced motion of small viscoelastic drops deposited on inclined lubricated surfaces. The viscoelastic fluids exhibit shear thinning and, more importantly, a significant first normal stress difference N1. Despite the homogeneity of the surface and of the fluids, drops of sufficiently high N1 move down with an oscillating instantaneous speed whose frequency is found to be directly proportional to the average speed and inversely to the drop volume. The oscillatory motion is caused by the formation of a bulge at the drop rear that starts rolling around the moving drop.