Spreading control of an impacting droplet

Drop impact on a flat surface induces a symmetric spreading of the lamella, i.e., spreading in a circular shape. In contrast, during impact on an inclined or moving surface, the spreading becomes asymmetric due to a tangential velocity (Vt) arising along the surface. For the latter, a model we developed based on the Taylor-Culick theory can restore the symmetricity of the lamella by considering a wettability contrast. To demonstrate this effect, we proposed and fabricated a surface design with a stripe pattern on aluminium sheets to highlight the wettability contrast. On the condition of both normal Weber number (We_n= ρVn²D₀/σ) and tangential Weber number (We_t= ρVt²D₀/σ) below 300 to ensure an impact outcome of deposition for water droplet, the model predicts the corrected lamella shape in good agreement with experimental data. The model can effectively correct the deformed lamella when 0.5≤We_n/ We_t ≤2.