Role of polymer concentration and molecular weight on the rebounding behaviors of polymer solution droplet impacting on hydrophobic surfaces

The impacting and rebounding behaviors of droplets containing polyethylene oxide (PEO) on Teflon-coated hydrophobic surface are investigated using a high-speed imaging system. Maximum spreading of droplets are examined experimentally by varying the concentration of polymer solution. During the spreading of droplets, no significant energy dissipation is found in the PEO solution droplets tested in this study. Energy dissipation during the retraction of contact line increases with the increase in the concentration and molecular weight of the polymer. Molecular weight does not show any noticeable effect when the concentration of the polymer solution is lower than 0.03 wt%. Its effect increases when the concentration is higher than 0.03 wt%, and the energy dissipation increases (threefold) at 0.05 wt% concentration. In addition, the residue composed of small satellite droplets is optically observed. The retraction velocity of contact line is decreased on the area of residue, which adds friction on the surface. A semiempirical model of energy balance equation is derived to estimate the rebounding tendency of a polymer solution droplet as a function of maximum spreading factor, retraction velocity, and reduced concentration. The friction coefficient of the polymer solution shows a linear relationship with reduced concentration.