The role of dynamic surface tension and elasticity on the dynamics of drop impact

The drop dynamics of Newtonian and non-Newtonian fluids on smooth surfaces is studied experimentally using a high-speed drum camera to make observations at 1000 frames s(-1). The spreading and recoil of the drops is studied predominantly on Parafilm M surfaces to determine the factors that suppress, rebound on hydrophobic surfaces. Newtonian test fluids of varying shear viscosity and equilibrium surface tension were constructed to confirm the observations of drop dynamics by previous authors. Test fluids were also constructed with a similar shear viscosity and varying concentrations of surfactants to understand the contributing roles played by hydrodynamics and dynamic Surface tension in surfactant solutions. The critical micelle concentration is found to be significant in determining whether the drop dynamics correlate with the dynamic surface tension data from the maximum bubble pressure apparatus. The influence of elasticity on drop recoil is also investigated using a carefully constructed group of elastic fluids of constant and equal shear viscosity. These constant viscosity elastic liquids were constructed by varying both the molecular weight and concentration of polymer, and the concentration of a Newtonian solvent to maintain a similar and constant shear viscosity. Both the increased molecular weight and concentration of polymer were found to be responsible for increased suppression of rebound on hydrophobic surfaces. (C) 2001 Published by Elsevier Science Ltd.