Effects of Interfacial and Viscous Properties of Liquids on Drop Spread Dynamics

An experimental study of the post-impact spreading of liquid droplets on dry horizontal substrates is presented in this paper. The drop spreading and recoil behaviors are captured using a high-speed digital video camera at 2000 frames per second. To ascertain the effects of liquid interfacial and viscous properties, experiments were conducted with five liquids (water, ethylene glycol, propylene glycol, glycerin, and acetic anhydride). A range of drop Weber number from 20 to 120 was considered by altering the height from which the drop is released. Effects of liquid properties on droplet spread-recoil dynamics were determined by comparing the results of liquids with different surface tension but similar viscosity and vice versa. The high-speed photographs of impact, spreading and recoil are shown and the temporal variations of dimensionless drop spread and height are provided in the paper. Results show that changes in liquid viscosity and surface tension significantly affect the spreading and recoil behavior. For a fixed Weber number, lower surface tension promotes greater spreading and higher viscosity dampens recoil. Also, spread, recoil and shape oscillations were more pronounced on a hydrophobic substrate (Teflon) compared to those on a hydrophilic substrate (glass). A detailed comparison of maximum spreads observed in the experiments with those obtained using spread correlations available in the literature show significant differences. Limitations of the available correlations are discussed in the paper. Corresponding author