SPREAD AND REBOUND OF LIQUID DROPLETS UPON IMPACT ON FLAT SURFACES

The spread and rebound of droplets upon impact on flat surfaces at roo m temperature were studied over a wide range of impact velocities (0.5 -6 m/s), viscosities (1-100 mPa.s), static contact angles (30-120 degr ees), droplet sizes (1.5-3.5 mm), and surface roughnesses using a fast -shutter-speed CCD camera. The maximum spread of a droplet upon impact depended strongly on the liquid viscosity and the impact velocity. Th e tendency of a droplet to deposit or to rebound is determined primari ly by the liquid viscosity and the liquid/substrate static contact ang le. A model more broadly applicable than existing models was developed to predict maximum spread as a function of the Reynolds number, the W eber number, and the static contact angle. Based on the conservation o f energy, a rebound model is proposed that predicts the tendency to re bound as a function of maximum spread and static contact angle. The ma ximum-spread model prediction agrees to within 10% with more than 90% of the experimental data from different sources. In the current study, the rebound model successfully predicts the tendency of a droplet to rebound.