Figure 5: Modelling of asymmetry in droplet shape.

An illustration of the physical mechanism behind the anisotropy in depinning contact angles and hence the formation of an octagonal droplet on a square array of cylindrical pillars. (a) Pillar density D/L is the critical parameter that dictates the depinning contact angles along the 0° line-of-sight (parallel to the axes of symmetry). Accordingly, the ratio of diameter D to apparent pitch is the appropriate parameter governing the depinning contact angles along the 45° line-of-sight. (b) The apparent contact angles along these two directions are not the same, resulting in the loss of circular symmetry of the droplet contact area. Different depinning contact angles along the two directions but with the same droplet height implies unequal base radii along these directions. Since there are a total of four axes of symmetry, (two along the 0° line-of-sight and two along the 45° line-of-sight), an eight-sided polygon, that is, an octagonal contact line, is formed.