Fig. 6.

Spontaneous wettability patterning on curved surfaces: (A) a cylindrical steel rod surface (15 mm in diameter), which has a mean curvature of $H=1/2\left(1/R_1+1/R_2\right)=0.067\hspace{0.5em}{\text{mm}}^{-1}$ and a Gaussian curvature of $K=1/\left(R_1{R}_2\right)=0$, and (B) a spherical glass lens surface (8 mm in radius, 2 mm in thickness at the apex of the lens), with $H=0.125\hspace{0.5em}{\text{mm}}^{-1}$ and $K=0.0156\hspace{0.5em}\mathrm{m}{\mathrm{m}}^{-2}$. (Scale bars, 500 μm.) ($R_1$ and $R_2$ are the two principal radii of a curved surface.)