The role of dynamic surface tension and elasticity on the dynamics of dropimpact

The drop dynamics of Newtonian and non-Newtonian fluids on smooth surfaces is studied experimentally using a high-speed drum camera to make observatio ns at 1000 frames s(-1). The spreading and recoil of the drops is studied p redominantly on Parafilm M surfaces to determine the factors that suppress, rebound on hydrophobic surfaces. Newtonian test fluids of varying shear vi scosity and equilibrium surface tension were constructed to confirm the obs ervations of drop dynamics by previous authors. Test fluids were also const ructed with a similar shear viscosity and varying concentrations of surfact ants to understand the contributing roles played by hydrodynamics and dynam ic Surface tension in surfactant solutions. The critical micelle concentrat ion is found to be significant in determining whether the drop dynamics cor relate with the dynamic surface tension data from the maximum bubble pressu re apparatus. The influence of elasticity on drop recoil is also investigat ed using a carefully constructed group of elastic fluids of constant and eq ual shear viscosity. These constant viscosity elastic liquids were construc ted 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 o n hydrophobic surfaces. (C) 2001 Published by Elsevier Science Ltd.