Figure 2.

(a) Plot of contact line position (x) vs. time (t) for droplets impacting onto surfaces with isotropic (unfilled symbols) and anisotropic wettability (filled symbols). Anisotropic surfaces consisted of hydrophilic arcs on a superhydrophobic background (see inset image). Upward and downward facing triangles indicate the contact line was located on a superhydrophobic or hydrophilic region, respectively (We = 10, r_o = 1.85 mm, w_o = 0.2 mm, D₀ = 2.9 mm). (b) Image sequence showing a water droplet impacting (We = 10) onto an anisotropic surface (hydrophilic arc on a superhydrophobic background; arc location indicated at 30.0 ms; refer to SI for a link to the full video, Video S1). The viewing angle is shown in the inset in (a). The positive x-direction (parallel to the surface) is indicated, as are the filled triangle symbols for the corresponding contact lines. Note how the contact lines on the left- and right-hand-side are free to move and pinned, respectively. At time 18.0 ms, the apparent contact angle values on the phobic () and philic () regions are indicated. Note the large difference between them. Scale bar in (b) is 1.0 mm.