Mapping the edge effect on polygonal pillars with three-dimensional drop imaging

Liquid drop shape on finite polygonal supports is governed by sharp-edge geometric pinning, which imposes an azimuthally non-uniform contact line. Understanding this coupling is relevant to the design of structured surfaces for controlled drop retention, spreading, and evaporation. Although edge pinning is well established, it remains unclear how the resulting macroscopic distortion propagates from the contact line into the bulk of a sessile drop. Water drops were deposited on circular, triangular, and square aluminum pillars and characterized using 360° rotational imaging. The azimuthal variation of the apparent contact angle was measured, three-dimensional drop geometry was reconstructed, and the height-dependent polygonal distortion was quantified using circularity and support-function Fourier modes. Polygonal pillars produced two repeatable wetting states: a maximum edge-effect state near the midpoints of the polygon sides and a lower-angle restrained-lamella state oriented toward the vertices. The angular contrast depended on pillar geometry and was largest for triangular pillars because their longer sides and larger side-to-vertex radial variation imposed the strongest azimuthal constraint. The reconstructed cross sections were non-circular near the solid surface and became more axisymmetric with height. The leading symmetry-compatible modes were (n = 3) for triangular pillars and (n = 4) for square pillars, while the first higher harmonics decayed more rapidly and remained concentrated closer to the surface. These trends were consistent with exponential relaxation predicted by a Young–Laplace-based perturbation framework. The circularity profiles indicated near-field curvature adjustment and global interface reshaping. The results provide three-dimensional quantification of how polygon-imposed contact-line distortions propagate into and relax through a sessile drop.