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 t o make observations at 1000 frarnes/s. A new technique was devised to estab lish when splash occurs on a hydrophilic surface. Experimental results for the onset of splash for Newtonian fluids agree with those of previous autho rs. The influence of elasticity on the onset of splash was examined using a carefully constructed group of elastic fluids of constant and equal viscos ity. These constant viscosity elastic liquids were constructed by varying t he polymer concentrations and Newtonian solvent concentrations to maintain a nearly constant shear viscosity and equilibrium surface tension. The appa rent extensional Viscosities for these materials increased dramatically wit h molecular weight. Great care was taken to eliminate the influence of dyna mic surface tension. Photographs of the elastic fluid drops impinging on me tal 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 fu nctional relationship between the threshold for splashing and a dimensionle ss roughness parameter. (C) 2000 The Society of Rheology. [S0148-6055(00)01 304-3].