Influence of fluid elasticity on drops impacting on dry surfaces

The impact of Newtonian and non-Newtonian fluids on surfaces of varying and known roughness is studied experimentally using a high-speed drum camera to make observations at 1000 frarnes/s. A new technique was devised to establish when splash occurs on a hydrophilic surface. Experimental results for the onset of splash for Newtonian fluids agree with those of previous authors. The influence of elasticity on the onset of splash was examined using a carefully constructed group of elastic fluids of constant and equal viscosity. These constant viscosity elastic liquids were constructed by varying the polymer concentrations and Newtonian solvent concentrations to maintain a nearly constant shear viscosity and equilibrium surface tension. The apparent extensional Viscosities for these materials increased dramatically with molecular weight. Great care was taken to eliminate the influence of dynamic surface tension. Photographs of the elastic fluid drops impinging on metal surfaces showed that the dilute polymer solutions exhibited splash and that the splash threshold increased with increasing Rouse relaxation time. All data obtained for the onset of splash can be collapsed onto a single functional relationship between the threshold for splashing and a dimensionless roughness parameter. (C) 2000 The Society of Rheology. [S0148-6055(00)01304-3].